docs(channels): example, README section, ROADMAP v0.6 mark-done — chunk 4

examples/channels_chat.rs (required-features phoenix): ephemeral
room:* and persistent session:* side by side over phoenix.js V2 JSON,
stdin-driven graceful shutdown (the ws_chat pattern). Smoke-tested
live: rejoin after transport drop lands on the same instance (state
counter persists across three transports), broadcasts carry the new
join generation's ref.

README: channels section (feature split, core trait walkthrough,
session persistence semantics incl. the re-entrant-join contract).
ROADMAP: v0.6 marked done with the full as-landed decision list,
chunked as committed.

.gitignore

@@ -1,2 +1,3 @@
 target
 Cargo.lock
+smarm_trace.json

Cargo.toml

@@ -9,9 +9,17 @@ description = "Cowboy/bandit-style HTTP library for the smarm actor runtime"
 smarm    = { path = "../smarm" }
 httparse = "1.9"
 libc     = "0.2"
+sha1_smol = "1"
+
+# dep #4, ratified 2026-06-12: serde/serde_json behind the opt-in
+# "phoenix" feature only — the "channels" core stays dependency-free.
+serde      = { version = "1", optional = true }
+serde_json = { version = "1", optional = true }
 
 [features]
 smarm-trace = ["smarm/smarm-trace"]
+channels    = []
+phoenix     = ["channels", "dep:serde", "dep:serde_json"]
 
 [dev-dependencies]
 serde      = { version = "1", features = ["derive"] }
@@ -28,3 +36,8 @@ codegen-units = 1
 [[example]]
 name = "crud"
 path = "examples/crud.rs"
+
+[[example]]
+name = "channels_chat"
+path = "examples/channels_chat.rs"
+required-features = ["phoenix"]

README.md

@@ -126,17 +126,304 @@ Handlers are closures taking `(Conn, Next) -> Conn`. Call `Next::call(c)` to con
 
 ```rust
 use urus::{serve_with, Config};
-use std::net::SocketAddr;
+use std::time::Duration;
 
 let cfg = Config {
-    listener_pool:     2,              // Number of OS threads handling accept()
-    scheduler_threads: Some(2),        // Number of smarm worker threads
+    listener_pool:      2,                        // Supervised accept-loop actors
+    scheduler_threads:  Some(2),                  // smarm worker threads (None = one per CPU)
+    keep_alive_timeout: Duration::from_secs(60),  // Idle budget between requests
+    request_timeout:    Duration::from_secs(30),  // Whole-request READ deadline
+    write_timeout:      Duration::from_secs(30),  // Per-write response budget
+    max_header_count:   64,
+    read_buf_size:      8 * 1024,
+    max_body_bytes:     1 << 20,
+    drain_timeout:      Duration::from_secs(30),  // Graceful-shutdown drain budget
     ..Config::new("127.0.0.1:8080".parse().unwrap())
 };
 
 serve_with(cfg, pipeline).unwrap();
 ```
 
+**Timeout semantics:**
+
+- `keep_alive_timeout` — how long a connection may sit idle waiting for the
+  *first byte* of a request. Expiry closes the socket silently (nothing was
+  in flight). Pipelined leftover bytes count as a started request, not idle.
+- `request_timeout` — a wall-clock deadline from a request's first byte
+  until its head and body are fully read. Expiry mid-head gets a
+  best-effort `408 Request Timeout`; expiry mid-body just closes. Deadlines
+  are absolute instants, so a trickling (slowloris-style) client can't
+  reset its budget by sending one byte at a time. Covers the **read phase
+  only** — a streaming response may legitimately outlive any whole-request
+  clock.
+- `write_timeout` — a per-write budget for response bytes: the fixed
+  head+body write, and *each* streamed chunk, must complete within it. A
+  client that stops reading is dropped once its socket buffer fills and a
+  write stalls past the budget (the write-side twin of slowloris). Streamed
+  chunks each get a fresh budget; a stream as a whole has no deadline.
+
+### Graceful Shutdown
+
+`serve_with_shutdown` takes a `ShutdownSignal`; the paired `Handle` can be
+triggered from anywhere (another thread, a signal handler):
+
+```rust
+use urus::{serve_with_shutdown, shutdown_handle, Config};
+
+let (handle, signal) = shutdown_handle();
+
+std::thread::spawn(move || {
+    // e.g. wait for SIGTERM / stdin / an admin endpoint...
+    handle.shutdown();
+});
+
+serve_with_shutdown(cfg, pipeline, signal).unwrap();
+// Returns once the runtime has fully wound down.
+```
+
+`Handle::shutdown()` is idempotent and performs, in order:
+
+1. Stop accepting — every listener exits; no new connections.
+2. Close idle keep-alive connections immediately.
+3. Drain in-flight requests for up to `Config.drain_timeout`.
+4. Force-stop any stragglers past the deadline (sockets close cleanly on
+   unwind via `OwnedFd::drop`).
+
+If every `Handle` is dropped, shutdown can never be signalled and the
+server runs forever — exactly `serve_with`'s semantics (it does this
+internally).
+
+### Streaming Responses
+
+A handler can return a body it doesn't have yet: hand urus the read end of
+a channel and feed it from a producer actor (the conn actor owns the
+socket and all write deadlines; the producer never touches the fd):
+
+```rust
+use urus::{Conn, Next};
+
+|c: Conn, _n: Next| {
+    let (tx, rx) = smarm::channel::<Vec<u8>>();
+    smarm::spawn(move || {
+        for part in ["chunk one", "chunk two"] {
+            if tx.send(part.as_bytes().to_vec()).is_err() {
+                return; // connection died — stop producing
+            }
+        }
+        // tx drops: end of stream.
+    });
+    c.put_status(200).put_body(rx)
+}
+```
+
+On HTTP/1.1 the response uses `Transfer-Encoding: chunked` and the
+connection is reusable afterwards; on HTTP/1.0 (no chunked framing) bytes
+go out raw and the connection closes to delimit the body. End of stream is
+signalled by dropping every `Sender`. The producer contract: a `send`
+error means the connection is gone — exit. Chunked **request** bodies are
+decoded transparently; handlers see `conn.body` either way.
+
+### Server-Sent Events
+
+`Conn::sse()` is the streaming body with the SSE headers and a heartbeat
+wired up:
+
+```rust
+|c: Conn, _n: Next| {
+    let (c, events) = c.sse(); // or c.sse_with_heartbeat(interval)
+    smarm::spawn(move || {
+        loop {
+            if events.send("tick", "data").is_err() {
+                return; // SseClosed: client gone or server draining
+            }
+            smarm::sleep(std::time::Duration::from_secs(1));
+        }
+    });
+    c
+}
+```
+
+While the producer is silent the connection actor emits `: keep-alive`
+comment chunks every `HEARTBEAT_INTERVAL` (15s default). Liveness comes
+from that ping: a vanished client is detected when a write stalls past
+`write_timeout`. No request clock applies to an open SSE stream, and a
+graceful shutdown force-stops it at the drain deadline.
+
+### Named Actors
+
+For introspection and debugging, the server registers itself in smarm's
+process registry: `urus.server` (the listener-pool supervisor) and
+`urus.listener.{i}` (each accept loop). `smarm::whereis(name)` resolves
+them from any actor inside the runtime.
+
+### WebSocket (v0.4)
+
+A route handler accepts the upgrade by handing `Conn::upgrade` a
+`WsHandler`; after the `101` the connection actor leaves HTTP and drives
+the handler from a duplex select loop (smarm RFC 008 fd arms: first-of
+outbound-channel / fd-readable, one actor, no fd dup):
+
+```rust
+struct Echo;
+
+impl urus::WsHandler for Echo {
+    fn on_message(&mut self, msg: urus::Message, sender: &urus::WsSender) {
+        let _ = sender.send(msg); // or .text(..) / .binary(..) / .ping() / .close(code, reason)
+    }
+    fn on_close(&mut self, code: Option<u16>, reason: &str) {
+        // what the PEER said: Some(code) iff its close frame arrived;
+        // None for EOF / write failure / handshake timeout.
+        let _ = (code, reason);
+    }
+}
+
+Router::new().get("/echo", |c: Conn, _n: Next| c.upgrade(Echo))
+```
+
+Callbacks run **inside the connection actor** — a slow `on_message`
+stops reads, which is backpressure, not a bug. A handler that wants
+concurrency spawns its own actor and hands it a `WsSender` clone (the
+SSE-producer pattern); every `WsSender` method returns `Err(WsClosed)`
+once the connection ends. While a large outbound frame is mid-write the
+actor isn't reading — accepted v1 trade-off of the one-actor topology.
+
+Control frames are invisible to the handler in v1: pings are
+auto-ponged, a peer close is auto-echoed and surfaces as `on_close`.
+Protocol violations close with the mapped RFC 6455 code (1002/1009/1007;
+handler panic → 1011). Caps: `Config.max_frame_payload` (1 MiB default,
+enforced from the frame header before payload buffers) and
+`Config.max_message_bytes` (4 MiB default, spans fragments).
+
+Like SSE, an open WebSocket has no request clock: idle is fine, a dead
+client is caught when a write stalls past `write_timeout`, and graceful
+shutdown force-stops the connection at the drain deadline. See
+`examples/ws_echo.rs`.
+
+The `WsHandler` trait also has a defaulted `on_open(&mut self, sender)`,
+called once before the frame loop — the place to subscribe or spawn
+producers for clients that may never send. Note the client sees the 101
+*before* `on_open` runs; a client that must know its subscriptions are
+live uses an application-level ack (any reply proves `on_open` completed,
+callbacks being sequential).
+
+## Pub/Sub (v0.5)
+
+`urus::pubsub` is a local-node, phoenix_pubsub-shaped topic broadcaster —
+independent of HTTP (it imports only smarm) and built for the WebSocket
+relay pattern:
+
+```rust
+let bus: PubSub<String> = PubSub::new();          // in-runtime only!
+let rx = bus.subscribe("room:lobby")?;            // Receiver<Arc<String>>
+bus.broadcast("room:lobby", "hi".to_string())?;
+bus.broadcast_from(smarm::self_pid(), "room:lobby", "no echo".into())?;
+```
+
+One generic instance per message domain; payloads broadcast as `Arc<M>`
+(one allocation per broadcast). `subscribe` is idempotent per
+`(pid, topic)` and pins the subscription to the **calling actor** — its
+death prunes the entry via a monitor; a dropped `Receiver` is pruned
+lazily on the next broadcast. `subscribe_as(pid, topic)` pins to an
+explicit pid for relay patterns. Mailboxes are unbounded: `broadcast`
+never blocks the table, and a slow subscriber's memory bill is bounded
+by the two cleanup paths above.
+
+Two composition rules that matter (both enforced by
+`shutdown_with_open_chat_terminates` in the integration suite):
+
+1. `PubSub::new()` spawns an actor, so it must run in-runtime — build it
+   lazily from a handler via a **non-static** `Arc<OnceLock<PubSub<M>>>`
+   captured by the route closure. A `static` cell pins the table actor
+   forever and graceful shutdown never returns.
+2. Relay/producer actors hold the `Receiver` (plus e.g. a `WsSender`
+   clone) — **never a `PubSub` clone**, or relay and table keep each
+   other alive past shutdown.
+
+See [`examples/ws_chat.rs`](examples/ws_chat.rs): rooms as topics,
+`on_open` subscribes + spawns the relay, `on_message` uses
+`broadcast_from` so the speaker isn't echoed.
+
+## Channels (v0.6)
+
+Phoenix-style join/leave/event multiplexing over the WebSocket duplex,
+pubsub underneath. Two additive features:
+
+- `channels` — the wire-neutral core (`Channel`, `ChannelHub`,
+  `PrefixRouter`, `ChannelSocket`, sessions). Zero new dependencies;
+  bring your own codec by implementing `Encode`/`Decode` for your
+  payload type.
+- `phoenix` — implies `channels`, adds serde/serde_json and the
+  phoenix.js V2 wire format via the `Json<T>` newtype.
+
+```rust
+use urus::{Channel, ChannelHub, ChannelSocket, PrefixRouter, Status};
+use urus::channels::phoenix::Json;
+use serde_json::{json, Value};
+
+type P = Json<Value>;
+
+#[derive(Default)]
+struct Room;
+
+impl Channel<P> for Room {
+    fn join(&mut self, topic: &str, payload: P, _s: &ChannelSocket<P>) -> Result<P, P> {
+        Ok(Json(json!({ "joined": topic })))   // Err(..) rejects
+    }
+    fn handle_in(&mut self, event: &str, payload: P, s: &ChannelSocket<P>) {
+        match event {
+            "shout" => s.broadcast("shouted", payload),
+            _ => s.reply(Status::Ok, Json(json!({ "echo": event }))),
+        }
+    }
+}
+
+// in-runtime, non-static — the ws_chat OnceLock pattern applies
+let hub = ChannelHub::new(PrefixRouter::new().channel_default::<Room>("room:*"));
+// route handler: hub.upgrade(conn)
+// from anywhere with a hub handle: hub.broadcast("room:lobby", "news", payload)
+```
+
+One channel actor per joined topic per socket, linked to the
+connection: callbacks are sequential, a channel panic is a socket
+event, and the conn-side handler answers transport heartbeats and
+routes joins — `Channel` impls never see frames or refs (`reply`
+correlates to the in-flight event invisibly).
+
+**Session persistence (opt-in).** By default channels cold-start per
+join, Phoenix-server style. Implementing `ChannelSession` and
+registering with `channel_session` makes the channel actor outlive its
+transport: broadcasts that arrive while detached are buffered (the same
+`Arc`s the relay path carries — zero re-serialisation) and drained, in
+order, under the rejoin's new generation. Buffer cap or TTL exceeded,
+explicit leave, or a rejected rejoin tears the session down; the next
+join is a cold start. A second transport claiming the same key evicts
+the first.
+
+```rust
+struct ByToken;
+impl urus::ChannelSession<P> for ByToken {
+    type Key = String;
+    fn session_key(topic: &str, join_payload: &P) -> String {
+        format!("{topic}/{}", join_payload.0["token"].as_str().unwrap_or(""))
+    }
+    // fn buffer_cap() -> usize { 128 }            // defaults
+    // fn ttl() -> Duration { Duration::from_secs(30) }
+}
+
+PrefixRouter::new().channel_session::<ByToken>("session:*", |_: &str| {
+    Box::new(Room::default()) as Box<dyn Channel<P>>
+})
+```
+
+Session channels must treat `join` as re-entrant: every reattach calls
+it again on the same instance (the rejoin ack needs a payload, and the
+channel gets to re-auth).
+
+See [`examples/channels_chat.rs`](examples/channels_chat.rs)
+(`cargo run --example channels_chat --features phoenix`): ephemeral
+`room:*` and persistent `session:*` side by side over phoenix.js V2
+JSON.
+
 ## Examples
 
 ### CRUD with Actor Ownership
@@ -165,11 +452,12 @@ cargo test
 ```
 
 Tests in `tests/integration.rs` cover:
-- Basic routing (GET, POST, PUT, DELETE)
-- Request body echoing
-- HTTP header parsing
-- Path parameter extraction
-- Status code responses
+- Basic routing, request bodies, headers, path parameters, status codes
+- Keep-alive and pipelining
+- Listener supervision (a panicking listener restarts without dropping a pending accept)
+- Graceful shutdown (idle close, in-flight drain, force-stop at the drain deadline)
+- Timeouts (idle keep-alive reaping, slowloris-style slow headers/body)
+- Registry names (`urus.server`, `urus.listener.{i}` resolve via `whereis`)
 
 ## Architecture
 
@@ -205,11 +493,11 @@ This avoids the complexity of async ecosystems while maintaining full concurrenc
 
 ## Roadmap
 
-v1 covers HTTP/1.1, the plug pipeline, and a built-in router. Future versions may include:
-- Middleware ecosystem (auth, logging, compression, etc.).
-- WebSocket support.
-- Benchmarking suite (see `urus-bench-spec.md`).
-- Additional utilities and examples.
+See [`ROADMAP.md`](ROADMAP.md). Summary: v0.2 (supervised listener pool,
+graceful shutdown, enforced timeouts, registry names), v0.3 (streaming
+bodies, chunked requests, SSE), v0.4 (WebSocket: handshake, frame
+codec, duplex handler API), v0.5 (PubSub) and v0.6 (Phoenix-style
+channels with opt-in session persistence) are done.
 
 Refer to `urus-spec.md` and `urus-v1-build-notes.md` in the artifact persistence for the original design and implementation notes.
 

ROADMAP.md

@@ -7,7 +7,8 @@
 
 ## State assessment (2026-06-11)
 
-Verified against smarm master (`v0.8`, slot slab + park-epoch + select):
+Verified against smarm master (`393cdd0`: v0.8 slot slab + park-epoch +
+select, plus RFC 008 phase 1 fd arms / timed fd waits):
 
 - **Builds clean, 24/24 tests pass.** The scheduler surface urus consumes
   (`spawn`, `wait_readable`, `wait_writable`, `sleep`, `init`, `Config`,
@@ -27,65 +28,85 @@ Verified against smarm master (`v0.8`, slot slab + park-epoch + select):
 - **No streaming response path.** `RespBody` is `Empty | Bytes`. Blocks SSE
   (a spec v1 goal that slipped) and chunked responses.
 - **Full-duplex constraint (matters for WebSocket).** smarm's epoll model is
-  one waiter per RawFd (`AlreadyExists` on the second registration) and one
-  direction per parked actor. Concurrent read+write on one connection needs
-  either the dup-fd trick (serve.rs already uses it for the listener pool)
-  or a new smarm primitive. Decide in v0.2 design, before the frame codec.
+  one waiter per RawFd (`AlreadyExists`, now surfaced as `Err` via the
+  `try_select` twins) and one direction per parked actor. RFC 008 phase 1
+  (landed `393cdd0`) gives first-of(fd, channel) via fd arms in select —
+  the duplex options in v0.4-3 are both open now. Decide in v0.4 design,
+  before the frame codec.
 
 ---
 
-## v0.2 — OTP refresh ⏳
+## v0.2 — OTP refresh ✅ (landed 2026-06, chunks 1-4 / commits 5fe6969..HEAD)
 
 Adopt the primitives urus predates. No protocol surface changes; `Plug`/`Conn`
 untouched. Chunks are independently landable, in order:
 
-### 1. Supervised listener pool
-Replace bare spawns in `serve_with` with a supervisor:
-`Strategy::OneForOne`, one `ChildSpec` per dup'd listener fd,
-`Restart::Permanent`. A listener panic restarts that listener; the pool
+### 1. Supervised listener pool ✅
+Landed: `serve_with` runs a `Strategy::OneForOne` supervisor on the root
+actor, one `ChildSpec` per dup'd listener fd, `Restart::Permanent`. A
+listener panic (or a transient `wait_readable` failure, which now exits
+and restarts instead of being fatal) restarts that listener; the pool
 never silently shrinks. Connection actors stay unsupervised bare spawns
 (per spec: a connection is cheap and its failure is local — a 500 path,
-not a restart path).
+not a restart path); `spawn` parents them under the listener, which has no
+supervisor channel, so their deaths are invisible to the pool supervisor
+by construction.
 
-Open question: should the restarted child re-dup from listener 0's fd, or
-own its fd across restarts via the ChildSpec closure? Leaning: closure
-captures the `OwnedFd`, re-registers on restart. No re-dup needed.
+Open question resolved as leaned: the ChildSpec factory owns the fd via
+`Arc<OwnedFd>` (`OwnedFd` gained `Sync` for this) and every (re)start
+reuses it. No re-dup, no window where a pool slot has no fd. Covered by
+`tests/integration.rs::panicking_listener_restarts` (pool of 1, panic
+injected before `accept` so the pending connection must survive into the
+restarted listener).
 
-### 2. Graceful shutdown
+### 2. Graceful shutdown ✅
+Landed (c658ac0): `serve_with_shutdown(config, pipeline, signal)` +
+`shutdown_handle()`. Drain-then-stop as decided below; design details in
+the commit body. `serve_with` keeps v1 run-forever semantics by dropping
+its own Handle.
 `serve_with` gains a shutdown signal (an `urus::Handle` with `.shutdown()`,
 backed by a channel + `request_stop` fan-out):
 1. Stop listeners (no new accepts; listener fds close).
-2. Stop connection actors — either drain-then-stop with a deadline, or
-   immediate `request_stop` (unwind closes fds cleanly via `OwnedFd::drop`).
+2. **Decided: drain-then-stop with a deadline** — in-flight requests get
+   to finish; `request_stop` after the deadline (unwind closes fds cleanly
+   via `OwnedFd::drop`). Drain also keeps the door open for an
+   apache-reload-style restart later.
 3. Supervisor winds down; `rt.run` returns; `serve_with` returns.
 
 Requires tracking live connection pids. Cheapest honest version: a
 `gen_server` connection registry — listener casts `{Started, pid}`, conn
-actor monitors-free self-deregisters via a drop guard cast. This registry
-is also chunk 3's reaper and the future ws/channels introspection point,
-so build it once here.
+actor monitors-free self-deregisters via a drop guard cast. Pid set only
+(no activity stamps — chunk 3 went per-conn timed waits, no reaper); still
+the future ws/channels introspection point, so build it once here.
 
-### 3. Enforce the timeouts we advertise
-**Decision fork — pick one before implementing:**
+### 3. Enforce the timeouts we advertise ✅
+Landed (a60687b): timed waits as decided below; the leaning held — a
+per-request `Instant` deadline keeps `request_timeout` an honest
+whole-request wall clock (mid-head expiry: best-effort non-parking 408;
+mid-body: close). Details in the commit body.
+**Decided: smarm-native timed waits** (the fork's option (a), a reaper in
+urus, died when RFC 008 landed at `393cdd0` — `wait_readable_timeout` /
+`wait_writable_timeout` exist upstream now, so there is nothing for the
+reaper to be the stopgap for):
 
-- **(a) Reaper in urus.** The chunk-2 registry tracks per-conn
-  `last_activity`; a ticker (`smarm::sleep` loop) sweeps and
-  `request_stop`s expired conns. Works today, zero smarm changes.
-  Granularity = sweep interval; conns must stamp activity (one cast per
-  request — measurable but small).
-- **(b) `wait_readable_timeout` in smarm.** A first-of(fd, timer) wait.
-  The v0.7 epoch-stamped consuming-unpark machinery exists precisely for
-  multi-arm waits (`select_timeout` is the channel-flavoured proof), but
-  fd arms aren't `Selectable` today — this is real smarm work in
-  `wait_fd`/io thread. Cleaner per-conn semantics, benefits every future
-  smarm io consumer, no reaper bookkeeping.
+`read_some` parks in `wait_readable_timeout` instead of `wait_readable`;
+`Ok(false)` means the deadline passed and the conn actor closes. Per-conn
+semantics, no activity stamping, no sweep ticker. Semantics note: a timed
+read wait enforces *idle-between-reads* — `keep_alive_timeout` between
+requests, and slowloris dies because each stalled read has a deadline.
+`request_timeout` as a whole-request wall clock is NOT what this gives;
+decide in implementation whether to track a per-request deadline across
+reads (cheap: one `Instant` in the conn loop, pass the min of both
+budgets to each wait) or redefine `request_timeout` as per-read. Leaning
+the `Instant`: it keeps the advertised config honest.
 
-Leaning **(a) now, (b) later**: (a) ships the security fix this cycle and
-the registry exists anyway; (b) becomes a smarm roadmap item whose landing
-lets the reaper's stamps go away. But if you'd rather not build throwaway:
-(b) first is defensible — say the word.
+urus is the first real consumer of the timed wrappers — note the RFC 008
+reviewer flag (`wait_fd` wraps in `NoPreempt`, select arms don't); the
+crud example under load doubles as that confirmation.
 
-### 4. Hygiene
+### 4. Hygiene ✅
+Landed: registry names + whereis test (in-runtime probe via a handler —
+tests are foreign threads), README rewrite, smarm-trace compile verified.
 - Registry names: `urus.server`, `urus.listener.{n}` via `smarm::register`
   (debuggability; `whereis` in tests).
 - README: rewrite Roadmap section to point here; document `Handle`.
@@ -98,81 +119,252 @@ panicking listener restarts under load without dropped accepts (test each).
 
 ---
 
-## v0.3 — Streaming bodies + SSE
+## v0.3 — Streaming bodies + SSE ✅ (landed 2026-06, chunks 1-3)
 
 The slipped v1 goal, and the WebSocket prerequisite (an upgraded connection
 is "a response that never ends").
 
-1. `RespBody::Stream(...)` — handler hands back a writer callback or a
-   `Receiver<Vec<u8>>`; conn actor switches to chunked transfer-encoding
-   (HTTP/1.1) and pumps until the stream closes. Keep-alive after a
-   completed chunked response.
-2. Chunked **request** bodies (`parser.rs` currently returns 411) — same
-   cycle, the codec knowledge is fresh.
-3. SSE sugar: `Conn::sse()` → an `EventSender` (`.send(event, data)`),
-   sets `content-type: text/event-stream`, disables buffering, heartbeats
-   via comment lines on a timer. An SSE conn is just a Stream body that
-   the reaper exempts from `request_timeout` (keep-alive ping instead).
+1. `RespBody::Stream(StreamBody)` ✅ — **decided: pull** (user call at the
+   v0.3 design fork): the handler hands back a `smarm::Receiver<Vec<u8>>`
+   and the producer is an actor the handler spawned; the conn actor pumps
+   (`pump_stream`) and keeps sole ownership of the socket and write
+   deadlines. The recv() park between chunks is stoppable by the draining
+   registry, so infinite streams die at the drain deadline with no
+   polling. HTTP/1.1: chunked TE, keep-alive after the terminator;
+   HTTP/1.0: raw bytes, forced close, EOF-delimited. End of stream =
+   every Sender dropped = 0-chunk. Timeout split (handoff Q3, as
+   proposed): `request_timeout` covers the READ phase only; new
+   `Config.write_timeout` (default 30s) bounds every response write —
+   fresh budget per streamed chunk, and the fixed-body + error-response
+   writes went deadline-bounded too (write-side slowloris closed).
+2. Chunked **request** bodies ✅ — `read_chunked_body` decodes
+   incrementally on the request deadline; extensions ignored, trailers
+   consumed + discarded, decoded size capped at max_body_bytes (413),
+   size-line/trailer spam capped (400). CL + TE: chunked, or chunked on
+   HTTP/1.0, rejected 400 at parse (smuggling ambiguity). Keep-alive
+   drain accounts RAW framing length, so pipelined requests behind a
+   chunked body land exactly.
+3. SSE sugar ✅ — `Conn::sse()` / `sse_with_heartbeat` → `EventSender`
+   (`send(event, data)` / `data` / `comment`, Clone, `Err(SseClosed)`
+   once the stream is gone). Heartbeat lives in the pump as leaned: with
+   `StreamBody.heartbeat` set, the chunk wait is `recv_timeout(interval)`
+   and expiry writes a `: keep-alive` comment chunk. Liveness from the
+   ping (dead client = heartbeat write stalls past write_timeout), not
+   from any request clock.
+
+**Exit criteria (verified):** chunked round-trips both directions with
+keep-alive and pipelining intact; an infinite SSE stream heartbeats while
+silent, is killed by write_timeout when the client stops reading, and is
+force-stopped at the drain deadline on shutdown; full suite green.
 
 ---
 
-## v0.4 — WebSocket upgrade path
+## v0.4 — WebSocket upgrade path ✅ (landed 2026-06, chunks 1-3)
 
-1. **Handshake**: detect `Connection: Upgrade` + `Upgrade: websocket` in
-   the pipeline; `Conn::upgrade(handler)` short-circuits — conn actor
-   validates `Sec-WebSocket-Key`, emits 101, exits the HTTP loop.
-   (SHA-1 + base64 needed; vendor a tiny SHA-1 rather than pulling a
-   crate — urus has two deps and it should stay that way.)
-2. **Frame codec**: RFC 6455 framing — fragmentation, masking (client
-   frames are always masked), control frames (ping/pong/close), 125-byte
-   control-payload rule, close-code handshake.
-3. **Duplex topology** (the design decision from the assessment):
-   - **(a) Two actors, dup'd fd**: reader actor on the dup, writer actor
-     on the original, writer owns a `Receiver<Frame>`; the user handler
-     talks to both via channels. Proven trick (listener pool), works today.
-   - **(b) One actor, smarm first-of(fd-readable, channel)**: needs fd
-     arms in select — the same smarm work as v0.2-3(b). Simpler topology,
-     no dup, but blocked on smarm.
-   Default (a); revisit if (b) lands for timeouts anyway.
-4. Handler API sketch (settle in design pass): trait with
-   `on_message/on_close` + a `WsSender` handle — gen_server-shaped, so a
-   ws connection *is* an actor you can monitor, link, and register.
+1. **Handshake** ✅ (49538cc) — `Conn::upgrade()` (handler arg comes
+   with chunk 3): §4.2.1 validation, 101 + accept key, marker field on
+   `Conn`, actor leaves the HTTP loop (fd drops until chunk 3 takes
+   over). Rejections stay plain HTTP (400 / 426 + version header) with
+   keep-alive intact. **Dep decision changed at the design pass**: SHA-1
+   is `sha1_smol` (zero transitive deps) — dep #3 SPENT, no hand-rolled
+   crypto (user call). The v0.6 JSON question is therefore a dep #4
+   question now. Base64 stays in-tree, encode-only.
+2. **Frame codec** ✅ (2869153) — pure `ws::frame`: incremental
+   `decode` (mask-required server mode), minimal-length + RSV + control
+   rules enforced, header-derived cap check before payload buffering,
+   close-code wire validation, `Assembler` for fragmentation with
+   whole-message UTF-8 check, `FrameError`→close-code map
+   (1002/1009/1007). §5.7 examples pinned verbatim.
+3. **Duplex wiring** ✅ — topology decision: **(b) one actor, RFC 008
+   fd arms** (urus exists to put smarm through its paces; first fd-arm
+   consumer is the point). As landed:
+   - `ws::duplex::run_duplex` replaces the HTTP loop after the 101:
+     `try_select(&[&outbound_rx, &FdArm::readable(fd)])` per iteration —
+     outbound at index 0 (select is priority-ordered: owed writes drain
+     before reading more). Accepted gap documented: mid-write of a large
+     outbound frame the actor isn't reading.
+   - Handler API (the deferred questions, as answered): in-actor
+     callbacks — `WsHandler { on_message, on_close }` runs inside the
+     select loop; concurrency = spawn your own actor with a `WsSender`
+     clone (the SSE-producer pattern). `Conn::upgrade(self, handler)`
+     flat signature (builder deferred until per-upgrade options exist,
+     e.g. subprotocols). `WsSender`: Clone, `send/text/binary/ping/
+     close → Err(WsClosed)`, unbounded channel like SSE (slow client
+     bounded by write_timeout). Control frames invisible v1: auto-pong
+     inline (§5.5.2), peer close auto-echoed (§5.5.1, server closes TCP
+     first per §7.1.1) surfacing only as `on_close(Some(code), reason)`;
+     wordless endings (EOF, write failure, handshake timeout) =
+     `on_close(None, "")`. `on_ping`/`on_pong` can land later as default
+     trait methods, non-breaking.
+   - Server-initiated close (WsSender::close or FrameError→1002/1009/
+     1007, handler panic→1011): close frame out, then a bounded drain
+     (one write_timeout budget) for the peer's echo, discarding data
+     (§1.4). Handler panics re-raise smarm's stop sentinel before being
+     treated as panics — the pipeline's catch_unwind dance, replicated.
+   - Caps: `Config.max_frame_payload` (1 MiB) / `max_message_bytes`
+     (4 MiB) — Config fields per the max_body_bytes precedent; header
+     cap checked before payload buffers.
+   - Buf handover: bytes pipelined past the upgrade head carry into the
+     duplex loop (tested).
+   - Registry: conn stays **Busy** for the ws lifetime (an open ws is
+     in-flight work); graceful shutdown force-stops it out of the select
+     park at the drain deadline (tested — the in-runtime request_stop
+     wake covers select parks, not just channel recv).
+   - Validated against a real client (python websocket-client): echo,
+     ping/pong payload, close handshake. `examples/ws_echo.rs` shows
+     both handler shapes (/echo in-actor, /clock producer-spawning).
+4. **Handler API** ✅ — folded into chunk 3 above (was: settle in design
+   pass; settled: gen_server-shaped trait + WsSender handle).
 
-## v0.5 — PubSub
+## v0.5 — PubSub ✅ (landed 2026-06, chunks 1-2)
 
 `urus::pubsub`, phoenix_pubsub-shaped, local node only (no distribution —
-smarm has none):
+smarm has none). All six design questions ratified by the user pre-code
+("push" on the stated leans); as-landed:
 
-- `subscribe(topic)`, `unsubscribe(topic)`, `broadcast(topic, msg)`,
-  `broadcast_from(self, topic, msg)`.
-- Topic table: gen_server owning `HashMap<Topic, Vec<(Pid, Sender<Arc<M>>)>>`;
-  shard N ways by topic hash if the single server measures hot (don't
-  pre-shard; bench first — smarm channel sends are cheap).
-- Dead subscriber cleanup via `monitor` + `handle_down` (this is exactly
-  what 06-10's gen_server `handle_down` was built for).
-- `Arc<M>` payloads: one allocation per broadcast, not per subscriber —
-  the shared-heap advantage over BEAM, take it.
+- **Generic `PubSub<M>`** per instance (Q1); heterogeneous buses are an
+  app-side enum. `Arc<M>` payloads: one allocation per broadcast.
+- **`subscribe(topic) -> Receiver<Arc<M>>`** (Q2), fresh channel per
+  subscription; `subscribe_as(pid, ..)` pins lifetime to an explicit pid
+  for relay shapes. Sender-passing fan-in (`subscribe_with`) deliberately
+  deferred — compatible addition.
+- **Unbounded mailboxes** (Q3): broadcast never blocks the table. Cleanup
+  is monitor `Down` (eager, on subscriber death) + prune-on-send-failure
+  (lazy, dropped receivers). Bench before sharding.
+- **User-owned handle** (Q4). The ratified register-by-name helper turned
+  out NOT implementable: smarm's registry maps name → Pid and a Pid can't
+  be turned back into a `ServerRef`. Deferred pending smarm support (or a
+  type-erased global, rejected). `pid()` exposed.
+- **Unique per `(pid, topic)`** (Q5): subscribe idempotent (replaces the
+  sender; the stale receiver closes). One monitor per live pid.
+  `handle_down` is a full table scan as ratified; pid→topics reverse
+  index is the documented optimization if deaths measure hot.
+- Table: gen_server `HashMap<Topic, HashMap<Pid, Sender<Arc<M>>>>` —
+  single server, not sharded (bench first). `subscriber_count(topic)`
+  added (tests need to observe async cleanup; legitimate API).
 
-Deliberately independent of HTTP — usable from any smarm app. Separate
-module now, candidate for crate extraction later.
+**Discoveries this cycle:**
+- `PubSub::new()` is in-runtime only (spawns the table actor) but
+  pipelines are built pre-runtime → the composition pattern is a
+  NON-static `Arc<OnceLock<PubSub<M>>>` in the route closure. Non-static
+  is load-bearing: the drained pipeline drops the cell in-runtime, the
+  table's inbox closes, the table exits, AllDone is reachable. A `static`
+  (crud's store shape) hangs `serve_with_shutdown`. Corollary: relays
+  hold `Receiver` only, never a `PubSub` clone (mutual-keepalive cycle).
+  Proven by `shutdown_with_open_chat_terminates`.
+- **`WsHandler::on_open(&mut self, sender)`** added (defaulted,
+  non-breaking): without it a listen-only ws client can never be
+  subscribed (`on_message` never fires). Same panic contract as
+  `on_message` (1011, no `on_close`). The 101 reaches the client before
+  `on_open` runs — subscription liveness needs an app-level ack
+  (documented; the integration tests use a `sync`/`synced` ack).
+- hammer.sh default subset now includes `ws_`.
 
-## v0.6 — Channels
+Chunk 2's ws_chat: rooms as topics, `on_open` subscribes (conn-actor
+pid) + spawns the relay, `broadcast_from(self_pid(), ..)` for no-echo.
 
-Phoenix channels: the join/leave/event protocol over WebSocket transport,
-PubSub underneath.
+## v0.6 — Channels — DONE (2026-06-12)
 
-- `Channel` trait: `join(topic, payload, socket)`, `handle_in(event,
-  payload, socket)`, `handle_out`, `terminate`.
-- Topic router (`"room:*"` patterns) → channel actor per (conn, topic),
-  spawned under the ws connection, linked so conn death reaps channels.
-- Wire format: Phoenix V2 JSON serializer
-  (`[join_ref, ref, topic, event, payload]`) — free interop with
-  phoenix.js clients is the killer feature; needs a JSON dep or a
-  hand-rolled mini-codec (decision point — this would be dep #3).
-- Presence: explicitly out of scope until distribution exists somewhere.
+Join/leave/event protocol over WebSocket transport, PubSub underneath.
+Design decisions ratified pre-code (2026-06-12):
+
+**Feature flags.** Two additive features:
+- `"channels"` — the `Channel` trait, `TopicRouter` trait, `PrefixRouter`,
+  `ChannelSocket`, session machinery. Zero new deps; pubsub is already
+  always-on (it only exists because channels needs it).
+- `"phoenix"` — implies `"channels"` + `serde`/`serde_json` + the V2 frame
+  codec. Opt-in phoenix.js interop; users who want protobuf or any other
+  wire format take `"channels"` only and supply their own codec.
+
+**Payload generics.** The `Channel` trait is generic over payload:
+`P: Encode + Decode` where `Encode`/`Decode` are urus codec traits (one
+method each). The `"phoenix"` feature provides a `JsonCodec` blanket impl
+via serde. No JSON anywhere in the `"channels"` surface.
+
+**`Channel` trait shape.**
+```
+trait Channel<P>: Send + 'static {
+    fn join(topic: &str, payload: P, socket: &ChannelSocket<P>) -> Result<P, P>;
+    fn handle_in(&mut self, event: &str, payload: P, socket: &ChannelSocket<P>);
+    fn terminate(&mut self) {}
+}
+```
+`handle_out` deferred — can land as a defaulted method, non-breaking.
+
+**`ChannelSocket`.** Newtype over `WsSender` + a `PubSub` handle.
+Exposes `reply(ref, status, payload)`, `push(event, payload)`,
+`broadcast(topic, payload)`. The `ref` from the incoming frame is threaded
+in by the channel actor loop, invisible to the impl. Coupling to `PubSub`
+is intentional: channels owns pubsub, and broadcast is the core use case.
+
+**Topic router.** `TopicRouter` trait: `fn route(&self, topic: &str) ->
+Option<Box<dyn ChannelFactory<P>>>`. Factory receives the full raw topic
+string so wildcard-segment extraction is always possible. urus ships
+`PrefixRouter` as the default impl: scan to `'*'`, discard the rest,
+single `HashMap` lookup on the prefix. No regex dep, no glob machinery —
+users who need that implement `TopicRouter` themselves.
+
+**Channel actor lifetime + session persistence.**
+Default: channel actor linked to the ws connection actor, cold-start on
+every reconnect (phoenix-server-compatible behavior). Opt-in persistence
+via a `ChannelSession` trait:
+```
+trait ChannelSession: Send + 'static {
+    type Key: Eq + Hash + Send + 'static;
+    fn session_key(topic: &str, join_payload: &P) -> Self::Key;
+    fn buffer_cap() -> usize { 128 }
+    fn ttl() -> Duration { Duration::from_secs(30) }
+}
+```
+When implemented, the router consults a session registry (gen_server,
+same pattern as the connection registry) before spawning: an existing
+actor is reattached, and buffered outbound messages (`Vec<Arc<M>>`, no
+re-serialisation) are drained to the reconnecting transport. Buffer full
+or TTL expired → actor tears down; next join is a cold start. This
+diverges from Phoenix server conventions (client-re-syncs) but is
+invisible to phoenix.js at the wire level. Zero-copy drain is the smarm
+motivation: messages are `Arc<M>` in the buffer and in the PubSub relay
+path, one allocation per broadcast regardless of subscriber count or
+reconnect cycles.
+
+**Presence:** explicitly out of scope until distribution exists.
+
+**As-landed (2026-06-12), beyond the ratified text — veto by diff:**
+- chunk 1: `Channel::join` takes `&mut self` (state from join, and
+  session rejoins need the same instance); the in-flight ref is
+  threaded invisibly through the socket; `broadcast` gained an `event`
+  parameter; `TopicRouter::route` returns `Option<Arc<dyn
+  ChannelFactory>>`.
+- chunk 2: the serde blanket lives behind the `Json<T>` newtype
+  (a blanket on bare `P: Serialize` is coherence poison under additive
+  features); encode failure panics into the linked-teardown contract.
+- chunk 3: `ChannelFactory` gained a `#[doc(hidden)] deploy()` seam
+  (default = the ephemeral linked actor); every attach re-calls
+  `join()` (re-entrant by contract); rejected rejoin / explicit leave /
+  cap / TTL all end the session; second transport evicts the first;
+  `Key: Clone` (registry's pid→key reverse index); registry spawns
+  eagerly at registration (in-runtime law, same as `ChannelHub::new`);
+  shutdown composes linklessly via the registry-drop chain — proven by
+  `shutdown_with_detached_session_terminates`.
 
 ---
 
+## Known bugs
+
+- ~~**HTTP/1.0 keep-alive: server honors but never advertises**~~ FIXED
+  (2026-06-12, same session it was found). As-landed decisions:
+  serialise_response now echoes `connection: keep-alive` on a kept-alive
+  1.0 response (1.1 keep-alive stays implicit); error statuses (>=400)
+  on 1.0 force close — no keep-alive advertised on a 4xx/5xx where reuse
+  is opt-in (conn_actor, alongside the existing 1.0-stream force-close);
+  HEAD needs nothing special (header echo only, framing untouched);
+  parse-error responses already carried `connection: close`. Validated
+  against the original repro: `ab -k -n 5000 -c 50` on GET /users now
+  reports 5000/5000 keep-alive requests, 0 failed, ~63k req/s
+  (vs ~18.9k no-keep-alive baseline, same box). Watch out benching:
+  ab counts a response toward "Non-2xx" silently — a 404'd route still
+  shows "Failed requests: 0" with great rps; check the route first.
+
 ## Later / icebox
 
 - **HTTP/2** — spec §2.2 already designs the stream-actor demux (zero-copy
@@ -182,8 +374,6 @@ PubSub underneath.
 - **SSE ergonomics round 2** — auto-reconnect support (`Last-Event-ID`),
   event-id bookkeeping, backpressure policy on slow consumers.
 - **TLS** — still deferred; acceptor design still must not preclude it.
-- **`wait_readable_timeout` / fd-in-select upstreaming** — the smarm-side
-  item that simplifies v0.2-3 and v0.4-3 retroactively.
 - **Middleware ecosystem** — compression, static files, auth plugs.
 - **Bench suite** — `urus-bench-spec.md` exists in the artefact store;
   wire it up once v0.2 lands (supervision changes the hot path not at all,

examples/channels_chat.rs

@@ -0,0 +1,117 @@
+//! Phoenix-style channels (v0.6): join/leave/event protocol over the
+//! v0.4 WebSocket duplex, pubsub underneath, phoenix V2 JSON on the
+//! wire.
+//!
+//!   cargo run --example channels_chat --features phoenix
+//!   websocat ws://127.0.0.1:8080/socket          (run two of these)
+//!   ["1","1","room:lobby","phx_join",{"name":"alice"}]
+//!   ["1","2","room:lobby","shout",{"text":"hi"}]
+//!   ["1","3","room:lobby","phx_leave",{}]
+//!
+//! The shapes this demonstrates:
+//!
+//! - **One `ChannelHub` for the whole app**, built lazily on the first
+//!   connection via the NON-static `Arc<OnceLock<...>>` pattern (the
+//!   hub spawns the pubsub table; same in-runtime + shutdown laws as
+//!   `examples/ws_chat.rs`, see the docs there).
+//!
+//! - **A channel per joined topic, not per socket.** `Room` never sees
+//!   frames, refs, or the transport heartbeat — the conn-side handler
+//!   answers heartbeats, routes `phx_join`, and the per-join channel
+//!   actor (linked to the connection) runs the callbacks sequentially.
+//!
+//! - **`Json<T>` is the phoenix codec's opt-in newtype.** The
+//!   `"channels"` core is wire-neutral (`Encode`/`Decode`, zero deps);
+//!   `Json<Value>` here buys phoenix.js V2 interop. Typed payloads work
+//!   the same way: `Json<MyPayload>` for any serde type.
+//!
+//! - **`session::*` topics persist across reconnects** (opt-in via
+//!   `channel_session`): drop a websocat mid-room, reconnect and rejoin
+//!   within 30s, and the broadcasts you missed drain to you in order —
+//!   the buffer holds the relay path's own `Arc`s, nothing is copied.
+//!   The session is keyed by the `"name"` in the join payload.
+
+use std::sync::{Arc, OnceLock};
+
+use serde_json::{json, Value};
+use urus::channels::phoenix::Json;
+use urus::{
+    serve_with_shutdown, shutdown_handle, Channel, ChannelHub, ChannelSession, ChannelSocket,
+    Config, Conn, Next, Pipeline, PrefixRouter, Router, Status,
+};
+
+type P = Json<Value>;
+
+/// One chat room. State lives across callbacks (and, for `session:*`
+/// topics, across transports).
+#[derive(Default)]
+struct Room {
+    name: String,
+    msgs_seen: u64,
+}
+
+impl Channel<P> for Room {
+    fn join(&mut self, topic: &str, payload: P, _s: &ChannelSocket<P>) -> Result<P, P> {
+        // Re-entrant by contract for session topics: a rejoin lands
+        // here again on the same instance — re-auth, then ack.
+        self.name = payload.0["name"].as_str().unwrap_or("anon").to_string();
+        Ok(Json(json!({ "joined": topic, "as": self.name, "seen": self.msgs_seen })))
+    }
+
+    fn handle_in(&mut self, event: &str, payload: P, s: &ChannelSocket<P>) {
+        match event {
+            "shout" => {
+                self.msgs_seen += 1;
+                s.broadcast("shouted", Json(json!({ "from": self.name, "msg": payload.0 })));
+            }
+            _ => s.reply(Status::Ok, Json(json!({ "echo": event }))),
+        }
+    }
+
+    fn terminate(&mut self) {
+        println!("room channel for {:?} is over", self.name);
+    }
+}
+
+/// Session config for `session:*`: the join payload's `"name"` is the
+/// session token. Defaults: 128 buffered broadcasts, 30s TTL.
+struct BySessionName;
+
+impl ChannelSession<P> for BySessionName {
+    type Key = String;
+    fn session_key(topic: &str, join_payload: &P) -> String {
+        format!("{topic}/{}", join_payload.0["name"].as_str().unwrap_or("anon"))
+    }
+}
+
+fn main() {
+    let hub: Arc<OnceLock<ChannelHub<P>>> = Arc::new(OnceLock::new());
+
+    let router = Router::new().get("/socket", move |c: Conn, _n: Next| {
+        // Hub construction is in-runtime only (it spawns the pubsub
+        // table and, for session patterns, their registries); the
+        // non-static cell is what lets shutdown drain them all.
+        let hub = hub.get_or_init(|| {
+            ChannelHub::new(
+                PrefixRouter::new()
+                    .channel_default::<Room>("room:*")
+                    .channel_session::<BySessionName>("session:*", |_: &str| {
+                        Box::new(Room::default()) as Box<dyn Channel<P>>
+                    }),
+            )
+        });
+        hub.upgrade(c)
+    });
+
+    let (handle, signal) = shutdown_handle();
+    std::thread::spawn(move || {
+        println!("channels_chat on ws://127.0.0.1:8080/socket — press Enter to shut down");
+        let mut line = String::new();
+        let _ = std::io::stdin().read_line(&mut line);
+        handle.shutdown();
+    });
+
+    serve_with_shutdown(Config::new("0.0.0.0:8080".parse().unwrap()), Pipeline::new().plug(router), signal)
+        .unwrap();
+    println!("channels_chat: drained, bye");
+}

examples/crud.rs

@@ -25,7 +25,7 @@
 use serde::{Deserialize, Serialize};
 use smarm::{channel, Sender};
 use std::sync::OnceLock;
-use urus::{serve_with, Config, Conn, Next, Pipeline, Router};
+use urus::{serve_with_shutdown, shutdown_handle, Config, Conn, Next, Pipeline, Router};
 
 // ---------------------------------------------------------------------------
 // Domain
@@ -78,8 +78,19 @@ fn store_loop(rx: smarm::Receiver<Request>) {
     let mut next_id: u64 = users.iter().map(|u| u.id).max().unwrap_or(0) + 1;
 
     loop {
-        let req = match rx.recv() {
+        // recv with a timeout rather than a bare recv: the store must be
+        // stoppable at shutdown, but a cross-thread Sender::send (from the
+        // stdin thread) can't wake a parked actor — same smarm limitation
+        // that motivates urus's SHUTDOWN_POLL. So we wake on our own timer
+        // and poll the flag. This poll dies with that limitation too.
+        let req = match rx.recv_timeout(std::time::Duration::from_millis(250)) {
             Ok(r) => r,
+            Err(smarm::channel::RecvTimeoutError::Timeout) => {
+                if SHUTTING_DOWN.load(std::sync::atomic::Ordering::Relaxed) {
+                    return;
+                }
+                continue;
+            }
             Err(_) => return, // all senders dropped
         };
         match req {
@@ -165,6 +176,12 @@ fn persist(users: &[User]) {
 
 static STORE_TX: OnceLock<Sender<Request>> = OnceLock::new();
 
+// Set by the stdin thread at shutdown; the store actor polls it (see
+// store_loop). An always-on app actor that never returns would otherwise
+// block smarm's AllDone and keep serve_with_shutdown from returning.
+static SHUTTING_DOWN: std::sync::atomic::AtomicBool =
+    std::sync::atomic::AtomicBool::new(false);
+
 fn store() -> &'static Sender<Request> {
     STORE_TX.get_or_init(|| {
         let (tx, rx) = channel::<Request>();
@@ -187,6 +204,28 @@ fn parse_id(s: &str) -> Option<u64> {
 // Handlers
 // ---------------------------------------------------------------------------
 
+/// SSE demo: `curl -N localhost:8080/ticker` streams a tick every second
+/// (with `: keep-alive` comments if it ever goes quiet). The producer
+/// exits on SseClosed (client gone / write timeout / shutdown drain) or
+/// when the example is shutting down.
+fn ticker(conn: Conn, _next: Next) -> Conn {
+    let (conn, events) = conn.sse();
+    smarm::spawn(move || {
+        let mut n: u64 = 0;
+        loop {
+            if SHUTTING_DOWN.load(std::sync::atomic::Ordering::Relaxed) {
+                return; // dropping `events` ends the stream cleanly
+            }
+            if events.send("tick", &n.to_string()).is_err() {
+                return; // SseClosed
+            }
+            n += 1;
+            smarm::sleep(std::time::Duration::from_secs(1));
+        }
+    });
+    conn
+}
+
 fn list(conn: Conn, _next: Next) -> Conn {
     let (tx, rx) = channel::<(u16, Vec<u8>)>();
     store().send(Request::List { reply: tx }).ok();
@@ -261,10 +300,25 @@ fn main() {
                 .post(  "/users",     create)
                 .get(   "/users/:id", get_one)
                 .put(   "/users/:id", update)
-                .delete("/users/:id", delete),
+                .delete("/users/:id", delete)
+                .get(   "/ticker",    ticker),
         );
 
     let cfg = Config::new("127.0.0.1:8080".parse().unwrap());
     println!("urus-crud: DB at {DB_PATH}");
-    serve_with(cfg, pipeline).unwrap();
+    println!("urus-crud: listening on 127.0.0.1:8080 — press Enter to shut down");
+
+    // Graceful shutdown on stdin-Enter: a plain OS thread blocks on
+    // read_line and fires the handle. No signal handling crate needed.
+    let (handle, signal) = shutdown_handle();
+    std::thread::spawn(move || {
+        let mut line = String::new();
+        let _ = std::io::stdin().read_line(&mut line);
+        println!("urus-crud: shutting down (draining in-flight requests)…");
+        SHUTTING_DOWN.store(true, std::sync::atomic::Ordering::Relaxed);
+        handle.shutdown();
+    });
+
+    serve_with_shutdown(cfg, pipeline, signal).unwrap();
+    println!("urus-crud: bye");
 }

examples/ws_chat.rs

@@ -0,0 +1,128 @@
+//! WebSocket chat rooms (v0.5): `urus::pubsub` wired to the v0.4 duplex.
+//!
+//!   cargo run --example ws_chat
+//!   websocat ws://127.0.0.1:8080/chat/lobby     (run two of these)
+//!
+//! The shapes this demonstrates:
+//!
+//! - **One `PubSub<String>` for the whole app**, topics are rooms
+//!   (`room:{name}`). Built lazily on the first connection via a
+//!   NON-static `Arc<OnceLock<PubSub>>` captured by the route closure:
+//!   `PubSub::new()` spawns the table actor, which smarm only allows
+//!   in-runtime — and keeping the cell non-static means the table's
+//!   last handle drops in-runtime when the drained pipeline drops, so
+//!   `serve_with_shutdown` actually returns. A `static` cell would pin
+//!   the table forever and block smarm's all-done. (Same constraint
+//!   crud's store solves with its OnceLock; the non-static refinement
+//!   is what makes graceful shutdown compose.)
+//!
+//! - **`on_open` subscribes and spawns the relay** — a listen-only
+//!   client receives the room without ever sending. The subscription is
+//!   pinned to the CONNECTION actor (`on_open` runs inside it), so the
+//!   monitor cleans up exactly when the connection dies.
+//!
+//! - **The relay holds the `Receiver` and a `WsSender` clone — and
+//!   deliberately NOT a `PubSub` handle.** A relay holding the handle
+//!   keeps the table's inbox open while the table keeps the relay's
+//!   receiver open: neither ever exits, and shutdown hangs. Receiver
+//!   only: conn dies → monitor prunes → sender drops → relay's recv
+//!   errs → relay exits. Every link in that chain is in-runtime.
+
+use std::sync::{Arc, OnceLock};
+
+use urus::{
+    serve_with_shutdown, shutdown_handle, Config, Conn, Message, Next, Pipeline, PubSub, Router,
+    WsHandler, WsSender,
+};
+
+type Bus = PubSub<String>;
+
+struct ChatHandler {
+    bus: Arc<OnceLock<Bus>>,
+    room: String,
+}
+
+impl ChatHandler {
+    fn topic(&self) -> String {
+        format!("room:{}", self.room)
+    }
+
+    fn bus(&self) -> &Bus {
+        // First connection anywhere spawns the table; we are inside the
+        // connection actor here, so the spawn is legal.
+        self.bus.get_or_init(PubSub::new)
+    }
+}
+
+impl WsHandler for ChatHandler {
+    fn on_open(&mut self, sender: &WsSender) {
+        let topic = self.topic();
+        let rx = match self.bus().subscribe(&topic) {
+            Ok(rx) => rx,
+            Err(_) => {
+                let _ = sender.close(1011, "chat bus down");
+                return;
+            }
+        };
+        let _ = self
+            .bus()
+            .broadcast_from(smarm::self_pid(), &topic, format!("* someone joined {topic}"));
+
+        // The relay: room messages -> this socket. Exits when the
+        // subscription is pruned (conn death / unsubscribe) or the
+        // socket is gone (WsClosed). See the module docs for why it
+        // must not capture a Bus handle.
+        let out = sender.clone();
+        smarm::spawn(move || {
+            while let Ok(msg) = rx.recv() {
+                if out.send(Message::Text((*msg).clone())).is_err() {
+                    break; // client gone or server draining
+                }
+            }
+        });
+    }
+
+    fn on_message(&mut self, msg: Message, sender: &WsSender) {
+        let Message::Text(text) = msg else {
+            let _ = sender.close(1003, "text only");
+            return;
+        };
+        // broadcast_from: the sender's own relay is skipped — no echo.
+        // self_pid() here is the connection actor, the pid on_open
+        // subscribed as.
+        let _ = self
+            .bus()
+            .broadcast_from(smarm::self_pid(), &self.topic(), text);
+    }
+
+    fn on_close(&mut self, _code: Option<u16>, _reason: &str) {
+        let topic = self.topic();
+        let _ = self
+            .bus()
+            .broadcast_from(smarm::self_pid(), &topic, format!("* someone left {topic}"));
+        // No explicit unsubscribe: the connection actor is about to
+        // exit and the monitor prunes the subscription (which is also
+        // what stops the relay).
+    }
+}
+
+fn main() {
+    let bus: Arc<OnceLock<Bus>> = Arc::new(OnceLock::new());
+
+    let pipeline = Pipeline::new().plug(Router::new().get("/chat/:room", move |c: Conn, _n: Next| {
+        let room = c.params.get("room").unwrap_or("lobby").to_string();
+        let bus = bus.clone();
+        c.upgrade(ChatHandler { bus, room })
+    }));
+
+    let (handle, signal) = shutdown_handle();
+    std::thread::spawn(move || {
+        println!("ws_chat on ws://127.0.0.1:8080/chat/:room — press Enter to shut down");
+        let mut line = String::new();
+        let _ = std::io::stdin().read_line(&mut line);
+        handle.shutdown();
+    });
+
+    serve_with_shutdown(Config::new("0.0.0.0:8080".parse().unwrap()), pipeline, signal).unwrap();
+    println!("ws_chat: drained, bye");
+}

examples/ws_echo.rs

@@ -0,0 +1,103 @@
+//! WebSocket echo server (v0.4).
+//!
+//!   cargo run --example ws_echo
+//!   websocat ws://127.0.0.1:8080/echo
+//!
+//! Demonstrates the chunk-3 handler model:
+//! - `EchoHandler` runs INSIDE the connection actor's select loop — echo
+//!   is exactly the workload that wants zero extra moving parts.
+//! - `/clock` shows the other shape: the handler spawns a producer actor
+//!   at `on_message("start")` and hands it a `WsSender` clone — the
+//!   SSE-producer pattern, verbatim. The producer exits when its send
+//!   fails (`WsClosed`: client gone or server shutting down).
+//!
+//! Routing happens before the upgrade, so one server can host both
+//! endpoints — `Conn::upgrade(handler)` is just another thing a route
+//! handler returns.
+
+use std::time::Duration;
+
+use urus::{
+    serve_with_shutdown, shutdown_handle, Config, Conn, Message, Next, Pipeline, Router,
+    WsHandler, WsSender,
+};
+
+// ---------------------------------------------------------------------------
+// /echo — everything comes straight back
+// ---------------------------------------------------------------------------
+
+struct EchoHandler;
+
+impl WsHandler for EchoHandler {
+    fn on_message(&mut self, msg: Message, sender: &WsSender) {
+        if matches!(&msg, Message::Text(t) if t == "bye") {
+            let _ = sender.close(1000, "you said bye");
+            return;
+        }
+        let _ = sender.send(msg);
+    }
+
+    fn on_close(&mut self, code: Option<u16>, reason: &str) {
+        println!("ws_echo: /echo closed (code {code:?}, reason {reason:?})");
+    }
+}
+
+// ---------------------------------------------------------------------------
+// /clock — "start" spawns a producer actor ticking once a second
+// ---------------------------------------------------------------------------
+
+struct ClockHandler {
+    started: bool,
+}
+
+impl WsHandler for ClockHandler {
+    fn on_message(&mut self, msg: Message, sender: &WsSender) {
+        match msg {
+            Message::Text(t) if t == "start" && !self.started => {
+                self.started = true;
+                let out = sender.clone();
+                smarm::spawn(move || {
+                    let mut n = 0u64;
+                    loop {
+                        if out.text(format!("tick {n}")).is_err() {
+                            return; // WsClosed: connection over, we follow
+                        }
+                        n += 1;
+                        smarm::sleep(Duration::from_secs(1));
+                    }
+                });
+            }
+            _ => {
+                let _ = sender.text("send \"start\" to begin");
+            }
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// main
+// ---------------------------------------------------------------------------
+
+fn main() {
+    let pipeline = Pipeline::new().plug(
+        Router::new()
+            .get("/echo", |c: Conn, _n: Next| c.upgrade(EchoHandler))
+            .get("/clock", |c: Conn, _n: Next| {
+                c.upgrade(ClockHandler { started: false })
+            }),
+    );
+
+    let cfg = Config::new("127.0.0.1:8080".parse().unwrap());
+    println!("ws_echo: ws://127.0.0.1:8080/echo and /clock — press Enter to shut down");
+
+    let (handle, signal) = shutdown_handle();
+    std::thread::spawn(move || {
+        let mut line = String::new();
+        let _ = std::io::stdin().read_line(&mut line);
+        println!("ws_echo: shutting down…");
+        handle.shutdown();
+    });
+
+    serve_with_shutdown(cfg, pipeline, signal).unwrap();
+    println!("ws_echo: bye");
+}

scripts/hammer.sh

@@ -0,0 +1,59 @@
+#!/usr/bin/env bash
+# Flake hammer: the conn-lifecycle test discipline, in one command.
+#
+# Default (no args) = the full pre-commit ritual for conn-lifecycle changes:
+#   1. N x the lifecycle-sensitive integration subset (fail-fast)
+#   2. M x the full suite (unit + integration + doc)
+#
+# Usage:
+#   scripts/hammer.sh                 # 35x subset + 3x full
+#   scripts/hammer.sh -n 50 -f 5      # override counts
+#   scripts/hammer.sh -n 20 -f 0 -- shutdown sse   # custom filter, skip full runs
+#
+# On failure: stops immediately, output of the failing run is in $LOG.
+
+set -u
+cd "$(dirname "$0")/.."
+export PATH="$HOME/.cargo/bin:$PATH"
+
+N=35
+FULL=3
+SUBSET=(shutdown timeout reaped slowloris streaming chunked sse stalled ws_)
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    -n) N="$2"; shift 2 ;;
+    -f) FULL="$2"; shift 2 ;;
+    --) shift; SUBSET=("$@"); break ;;
+    *) echo "unknown arg: $1" >&2; exit 2 ;;
+  esac
+done
+
+LOG=target/hammer-fail.log
+mkdir -p target
+
+echo "== build once =="
+cargo test --no-run --quiet || exit 1
+
+fail() { # $1 = label
+  echo
+  echo "FAILED at $1 — output in $LOG"
+  exit 1
+}
+
+echo "== ${N}x subset: ${SUBSET[*]} =="
+for ((i = 1; i <= N; i++)); do
+  printf '\r  subset %d/%d ' "$i" "$N"
+  cargo test --quiet --test integration -- "${SUBSET[@]}" >"$LOG" 2>&1 \
+    || fail "subset run $i/$N"
+done
+echo
+
+echo "== ${FULL}x full suite =="
+for ((i = 1; i <= FULL; i++)); do
+  printf '  full %d/%d\n' "$i" "$FULL"
+  cargo test --quiet >"$LOG" 2>&1 || fail "full run $i/$FULL"
+done
+
+rm -f "$LOG"
+echo "hammer green: ${N}x subset + ${FULL}x full"

src/channels/phoenix.rs

@@ -0,0 +1,223 @@
+//! Phoenix V2 wire codec — feature `"phoenix"` (implies `"channels"`,
+//! spends dependency slot #4 on `serde`/`serde_json`, ratified
+//! 2026-06-12).
+//!
+//! The wire format phoenix.js speaks: one JSON array per frame,
+//!
+//! ```text
+//! [join_ref, ref, topic, event, payload]
+//! ```
+//!
+//! refs are strings or `null`; replies are `event: "phx_reply"` with
+//! `payload: {"status": "ok"|"error", "response": <payload>}`.
+//!
+//! # `Json<T>`, not a blanket impl on `P`
+//!
+//! The ratified sketch said "JsonCodec blanket impl via serde". A
+//! literal `impl<P: Serialize + DeserializeOwned> Encode for P` is
+//! coherence poison: features are additive across a dependency graph,
+//! so the moment ANY crate enables `"phoenix"`, every hand-written
+//! `Encode` impl in every other crate stops compiling (the compiler
+//! cannot prove a foreign type will never gain `Serialize`). That
+//! breaks the design's own promise that `"channels"`-only users supply
+//! their own codecs. The blanket therefore lives one newtype away:
+//! [`Json<T>`] is V2-JSON for ANY serde-capable `T` — including
+//! `Json<serde_json::Value>` for schemaless payloads — while the
+//! `Encode`/`Decode` namespace stays open.
+//!
+//! # Strictness
+//!
+//! Decoding is exactly as strict as `T`'s `Deserialize`: a phoenix.js
+//! `{}` join payload fails against a `T` with required fields (the
+//! socket closes `1002`). Use `#[serde(default)]`, `Option` fields, or
+//! `Json<serde_json::Value>` where the client is loose. Encoding a `T`
+//! that fails `Serialize` (non-string map keys and friends) panics —
+//! that is a bug in the payload type, and the panic rides the
+//! documented channel-panic contract (linked teardown).
+
+use super::{
+    ChannelFrame, ChannelMessage, Decode, DecodeError, Encode, FrameRef, MessageRef, Status,
+    EV_REPLY,
+};
+use crate::ws::Message;
+
+use serde::de::DeserializeOwned;
+use serde::Serialize;
+use serde_json::{json, Map, Value};
+
+/// V2-JSON payload wrapper: `Json<T>` speaks the phoenix wire for any
+/// `T: Serialize + DeserializeOwned`. Derefs to `T`.
+#[derive(Debug, Clone, PartialEq, Eq, Default)]
+pub struct Json<T>(pub T);
+
+impl<T> std::ops::Deref for Json<T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        &self.0
+    }
+}
+impl<T> std::ops::DerefMut for Json<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.0
+    }
+}
+impl<T> From<T> for Json<T> {
+    fn from(t: T) -> Self {
+        Json(t)
+    }
+}
+
+fn empty_object() -> Value {
+    Value::Object(Map::new())
+}
+
+fn to_value<T: Serialize>(t: &T) -> Value {
+    serde_json::to_value(t).expect("phoenix codec: payload failed to serialize")
+}
+
+impl<T: Serialize + DeserializeOwned + Send + Sync + 'static> Encode for Json<T> {
+    fn encode(f: FrameRef<'_, Self>) -> Message {
+        let (event, payload) = match f.message {
+            MessageRef::Event { event, payload } => {
+                (event, payload.map(|p| to_value(&p.0)).unwrap_or_else(empty_object))
+            }
+            MessageRef::Reply { status, payload } => (
+                EV_REPLY,
+                json!({
+                    "status": match status {
+                        Status::Ok => "ok",
+                        Status::Error => "error",
+                    },
+                    "response": payload.map(|p| to_value(&p.0)).unwrap_or_else(empty_object),
+                }),
+            ),
+        };
+        let arr = json!([f.join_ref, f.reference, f.topic, event, payload]);
+        Message::Text(arr.to_string())
+    }
+}
+
+impl<T: Serialize + DeserializeOwned + Send + Sync + 'static> Decode for Json<T> {
+    fn decode(msg: &Message) -> Result<ChannelFrame<Self>, DecodeError> {
+        let Message::Text(s) = msg else {
+            return Err(DecodeError("phoenix V2 frames are text".into()));
+        };
+        let (join_ref, reference, topic, event, payload): (
+            Option<String>,
+            Option<String>,
+            String,
+            String,
+            Value,
+        ) = serde_json::from_str(s).map_err(|e| DecodeError(e.to_string()))?;
+
+        let message = if event == EV_REPLY {
+            // Clients don't reply in practice; decoded for symmetry
+            // (and ignored upstream).
+            let status = match payload.get("status").and_then(Value::as_str) {
+                Some("ok") => Status::Ok,
+                _ => Status::Error,
+            };
+            let response = payload.get("response").cloned().unwrap_or_else(empty_object);
+            let payload = serde_json::from_value::<T>(response)
+                .map_err(|e| DecodeError(format!("reply response: {e}")))?;
+            ChannelMessage::Reply { status, payload: Some(Json(payload)) }
+        } else {
+            let payload = serde_json::from_value::<T>(payload)
+                .map_err(|e| DecodeError(format!("payload for '{event}': {e}")))?;
+            ChannelMessage::Event { event, payload: Json(payload) }
+        };
+        Ok(ChannelFrame { join_ref, reference, topic, message })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    type V = Json<Value>;
+
+    fn parse(m: &Message) -> Value {
+        let Message::Text(s) = m else { panic!("not text") };
+        serde_json::from_str(s).unwrap()
+    }
+
+    #[test]
+    fn decodes_phoenix_js_join_frame() {
+        let m = Message::Text(r#"["3","3","room:lobby","phx_join",{"token":"t"}]"#.into());
+        let f = V::decode(&m).unwrap();
+        assert_eq!(f.join_ref.as_deref(), Some("3"));
+        assert_eq!(f.reference.as_deref(), Some("3"));
+        assert_eq!(f.topic, "room:lobby");
+        let ChannelMessage::Event { event, payload } = f.message else { panic!() };
+        assert_eq!(event, "phx_join");
+        assert_eq!(payload.0, json!({"token": "t"}));
+    }
+
+    #[test]
+    fn decodes_heartbeat_null_refs_allowed() {
+        let m = Message::Text(r#"[null,"7","phoenix","heartbeat",{}]"#.into());
+        let f = V::decode(&m).unwrap();
+        assert_eq!(f.join_ref, None);
+        assert_eq!(f.topic, "phoenix");
+    }
+
+    #[test]
+    fn encodes_ok_reply_with_status_response_wrapper() {
+        let p = Json(json!({"user_count": 2}));
+        let m = V::encode(FrameRef {
+            join_ref: Some("3"),
+            reference: Some("4"),
+            topic: "room:lobby",
+            message: MessageRef::Reply { status: Status::Ok, payload: Some(&p) },
+        });
+        assert_eq!(
+            parse(&m),
+            json!(["3", "4", "room:lobby", "phx_reply",
+                   {"status": "ok", "response": {"user_count": 2}}])
+        );
+    }
+
+    #[test]
+    fn encodes_payloadless_reply_and_event_as_empty_object() {
+        let m = V::encode(FrameRef {
+            join_ref: None,
+            reference: Some("9"),
+            topic: "phoenix",
+            message: MessageRef::Reply { status: Status::Ok, payload: None },
+        });
+        assert_eq!(
+            parse(&m),
+            json!([null, "9", "phoenix", "phx_reply", {"status": "ok", "response": {}}])
+        );
+        let m = V::encode(FrameRef {
+            join_ref: Some("3"),
+            reference: None,
+            topic: "room:lobby",
+            message: MessageRef::Event { event: "phx_close", payload: None },
+        });
+        assert_eq!(parse(&m), json!(["3", null, "room:lobby", "phx_close", {}]));
+    }
+
+    #[test]
+    fn typed_payload_round_trip_and_strictness() {
+        #[derive(serde::Serialize, serde::Deserialize, Debug, PartialEq)]
+        struct Chat {
+            body: String,
+        }
+        let m = Message::Text(r#"["1","2","room:a","new_msg",{"body":"hi"}]"#.into());
+        let f = Json::<Chat>::decode(&m).unwrap();
+        let ChannelMessage::Event { payload, .. } = f.message else { panic!() };
+        assert_eq!(payload.0, Chat { body: "hi".into() });
+
+        // Missing required field: the codec is as strict as T.
+        let m = Message::Text(r#"["1","2","room:a","new_msg",{}]"#.into());
+        assert!(Json::<Chat>::decode(&m).is_err());
+    }
+
+    #[test]
+    fn garbage_and_binary_are_decode_errors() {
+        assert!(V::decode(&Message::Text("not json".into())).is_err());
+        assert!(V::decode(&Message::Text(r#"{"a":1}"#.into())).is_err());
+        assert!(V::decode(&Message::Binary(vec![1, 2, 3])).is_err());
+    }
+}

src/channels/session.rs

@@ -0,0 +1,736 @@
+//! Opt-in channel session persistence (the ratified v0.6 design).
+//!
+//! Default channel lifetime is transport-bound: cold start per join,
+//! actor dies with the socket. A [`ChannelSession`] impl registered via
+//! [`PrefixRouter::channel_session`](super::PrefixRouter::channel_session)
+//! changes that: the channel actor outlives its transport, buffering
+//! outbound broadcasts (`VecDeque<Arc<Broadcast<P>>>` — the same `Arc`s
+//! the pubsub relay path carries, zero re-allocation) until the client
+//! rejoins, the buffer fills, or the TTL expires.
+//!
+//! Shape (one registry gen_server per `channel_session` registration,
+//! monomorphic over the session key — no type erasure):
+//!
+//! - `deploy` on the conn actor computes the session key and casts the
+//!   whole join handshake to the registry.
+//! - The registry owns `key -> (pid, control sender)`. Existing entry:
+//!   the handshake is forwarded as an `Attach` (reattach). Absent or
+//!   dead (send failure raced the monitor `Down`): spawn fresh,
+//!   monitor, insert. Down prunes, guarded by pid match against
+//!   replaced entries.
+//! - The session actor is **not linked** to any connection — outliving
+//!   the transport is the point. Its exits: explicit leave, rejected
+//!   (re)join, TTL expiry, buffer cap, pubsub relay death, or the
+//!   registry's control sender dropping — which is exactly the shutdown
+//!   chain (conns die -> router `Arc`s drop -> registry's inbox closes
+//!   -> registry exits -> control senders drop -> every parked session
+//!   wakes on the closed control arm, terminates, and exits; `AllDone`
+//!   composes without links).
+//!
+//! As-landed decisions (veto by diff):
+//! - **Every attach calls `ch.join()` again** on the same instance —
+//!   the client's `phx_join` needs an ack payload and the channel gets
+//!   to re-auth. Session channels must treat `join` as re-entrant.
+//! - **A rejected rejoin ends the session** (error reply, `terminate`,
+//!   exit): `Err` means "this transport may not have this channel", and
+//!   a zombie session held open for an unauthorized client is a
+//!   liability. Next join is a cold start.
+//! - **A second transport evicts the first** (best-effort `phx_close`
+//!   on the old socket): a session is single-transport by definition;
+//!   two tabs wanting independent channels should not share a session
+//!   key.
+//! - **TTL is per detach episode** (reset on every disconnect), and the
+//!   pubsub subscription is made once, on the first successful join, to
+//!   the first join's topic.
+//! - **`ChannelSession::Key: Clone`** beyond the ratified
+//!   `Eq + Hash + Send` — the registry keeps a `pid -> key` reverse
+//!   index for monitor-`Down` pruning.
+
+use super::*;
+
+use smarm::gen_server::{self, GenServer, ServerCtx};
+use smarm::{Down, ServerRef, Watcher};
+
+use std::collections::VecDeque;
+use std::hash::Hash;
+use std::time::{Duration, Instant};
+
+/// Opt-in session persistence config for a channel type. All methods
+/// are static: the config is consulted before any channel instance
+/// exists.
+pub trait ChannelSession<P>: Send + 'static {
+    /// What identifies "the same session" across reconnects.
+    type Key: Eq + Hash + Send + 'static;
+
+    /// Derive the session key from a join. Same key, same (live)
+    /// channel actor; the join payload is the natural carrier for a
+    /// client-held session token.
+    fn session_key(topic: &str, join_payload: &P) -> Self::Key;
+
+    /// Detached broadcasts buffered before the session tears itself
+    /// down (next join is a cold start).
+    fn buffer_cap() -> usize {
+        128
+    }
+
+    /// How long a detached session waits for a rejoin before tearing
+    /// itself down. Reset on every detach.
+    fn ttl() -> Duration {
+        Duration::from_secs(30)
+    }
+}
+
+// ---------------------------------------------------------------------------
+// The session-aware factory (what channel_session registers)
+// ---------------------------------------------------------------------------
+
+pub(super) struct SessionFactory<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> {
+    inner: Arc<dyn ChannelFactory<P>>,
+    keyfn: fn(&str, &P) -> K,
+    registry: ServerRef<Registry<P, K>>,
+}
+
+/// The registry's working bounds for a session key.
+pub(super) trait SessionKey: Eq + Hash + Clone + Send + 'static {}
+impl<K: Eq + Hash + Clone + Send + 'static> SessionKey for K {}
+
+impl<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> SessionFactory<P, K> {
+    /// **In-runtime only** — spawns the registry gen_server.
+    pub(super) fn new<S: ChannelSession<P, Key = K>>(inner: Arc<dyn ChannelFactory<P>>) -> Self {
+        let registry = gen_server::start(Registry {
+            factory: inner.clone(),
+            cap: S::buffer_cap(),
+            ttl: S::ttl(),
+            sessions: HashMap::new(),
+            pid_key: HashMap::new(),
+            watcher: None,
+        });
+        SessionFactory { inner, keyfn: S::session_key, registry }
+    }
+}
+
+impl<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> ChannelFactory<P>
+    for SessionFactory<P, K>
+{
+    fn create(&self, topic: &str) -> Box<dyn Channel<P>> {
+        self.inner.create(topic)
+    }
+
+    fn deploy(&self, hs: JoinHandshake<P>) -> ChannelInbox<P>
+    where
+        P: Encode + Decode,
+    {
+        let key = (self.keyfn)(&hs.topic, &hs.payload);
+        let (tx, rx) = smarm::channel::<In<P>>();
+        // Cast: the actor acks the join straight to the socket; the
+        // conn actor has nothing to wait for. A dead registry can only
+        // mean shutdown — the failed join is moot.
+        let _ = self.registry.cast(Join { key, hs, inbound: rx });
+        ChannelInbox(tx)
+    }
+}
+
+// ---------------------------------------------------------------------------
+// The registry gen_server: key -> live session actor
+// ---------------------------------------------------------------------------
+
+pub(super) struct Join<P: Send + Sync + 'static, K> {
+    key: K,
+    hs: JoinHandshake<P>,
+    inbound: Receiver<In<P>>,
+}
+
+struct Registry<P: Send + Sync + 'static, K> {
+    factory: Arc<dyn ChannelFactory<P>>,
+    cap: usize,
+    ttl: Duration,
+    sessions: HashMap<K, (Pid, Sender<Ctl<P>>)>,
+    /// Reverse index for `handle_down` — the reason `Key: Clone`.
+    pid_key: HashMap<Pid, K>,
+    watcher: Option<Watcher>,
+}
+
+impl<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> GenServer for Registry<P, K> {
+    type Call = ();
+    type Reply = ();
+    type Cast = Join<P, K>;
+    type Info = ();
+
+    fn init(&mut self, ctx: &ServerCtx) {
+        self.watcher = Some(ctx.watcher());
+    }
+
+    fn handle_call(&mut self, _request: ()) {}
+
+    fn handle_cast(&mut self, Join { key, hs, inbound }: Join<P, K>) {
+        let attach = Ctl::Attach { hs, inbound };
+        let attach = match self.sessions.get(&key) {
+            Some((_, ctl)) => match ctl.send(attach) {
+                Ok(()) => return, // reattached
+                // The actor died and its Down hasn't landed yet:
+                // recover the handshake, replace below.
+                Err(smarm::channel::SendError(a)) => a,
+            },
+            None => attach,
+        };
+        let (ctl_tx, ctl_rx) = smarm::channel::<Ctl<P>>();
+        let (factory, cap, ttl) = (self.factory.clone(), self.cap, self.ttl);
+        let pid = smarm::spawn(move || run_session(factory, cap, ttl, ctl_rx)).pid();
+        // Cannot fail: the receiver is owned by the just-spawned actor.
+        let _ = ctl_tx.send(attach);
+        self.watcher
+            .as_ref()
+            .expect("watcher set in init")
+            .watch(smarm::monitor(pid));
+        self.pid_key.insert(pid, key.clone());
+        self.sessions.insert(key, (pid, ctl_tx));
+    }
+
+    fn handle_down(&mut self, down: Down) {
+        if let Some(key) = self.pid_key.remove(&down.pid) {
+            // Pid guard: a stale Down for an entry handle_cast already
+            // replaced must not evict the replacement.
+            if self.sessions.get(&key).is_some_and(|(p, _)| *p == down.pid) {
+                self.sessions.remove(&key);
+            }
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// The session actor
+// ---------------------------------------------------------------------------
+
+enum Ctl<P: Send + Sync + 'static> {
+    Attach { hs: JoinHandshake<P>, inbound: Receiver<In<P>> },
+}
+
+enum Step<P: Send + Sync + 'static> {
+    Attach { hs: JoinHandshake<P>, inbound: Receiver<In<P>> },
+    Attached { inbound: Receiver<In<P>> },
+    Detached,
+    Exit,
+}
+
+fn run_session<P: Encode + Decode + Send + Sync + 'static>(
+    factory: Arc<dyn ChannelFactory<P>>,
+    cap: usize,
+    ttl: Duration,
+    ctl: Receiver<Ctl<P>>,
+) {
+    // The initial Attach is cast by the registry in the same handler
+    // that spawned us. Closed instead = registry died first (shutdown
+    // raced the spawn): nothing exists yet, nothing to clean.
+    let Ok(Ctl::Attach { hs, inbound }) = ctl.recv() else { return };
+
+    // Partial moves: ws/bus/topic/join_ref go into the socket,
+    // reference/payload stay behind for the first attach below.
+    let mut socket = ChannelSocket {
+        ws: hs.ws,
+        bus: hs.bus,
+        topic: hs.topic,
+        join_ref: hs.join_ref,
+        cur_ref: RefCell::new(None),
+    };
+    let mut ch: Option<Box<dyn Channel<P>>> = None;
+    let mut joined = false;
+    let mut bus_rx: Option<Receiver<Arc<Broadcast<P>>>> = None;
+    let mut buffer: VecDeque<Arc<Broadcast<P>>> = VecDeque::new();
+
+    let mut step = attach(
+        &factory,
+        &mut ch,
+        &mut joined,
+        &mut bus_rx,
+        &mut buffer,
+        &mut socket,
+        hs.reference,
+        hs.payload,
+        inbound,
+    );
+    loop {
+        step = match step {
+            Step::Attach { hs, inbound } => {
+                socket.ws = hs.ws;
+                socket.join_ref = hs.join_ref;
+                socket.topic = hs.topic;
+                attach(
+                    &factory,
+                    &mut ch,
+                    &mut joined,
+                    &mut bus_rx,
+                    &mut buffer,
+                    &mut socket,
+                    hs.reference,
+                    hs.payload,
+                    inbound,
+                )
+            }
+            Step::Attached { inbound } => attached_loop(
+                ch.as_deref_mut().expect("attached implies created"),
+                &socket,
+                &ctl,
+                &inbound,
+                bus_rx.as_ref().expect("attached implies subscribed"),
+                &mut buffer,
+            ),
+            Step::Detached => detached_loop(
+                &ctl,
+                bus_rx.as_ref().expect("detached only after first subscribe"),
+                &mut buffer,
+                cap,
+                ttl,
+            ),
+            Step::Exit => {
+                if joined {
+                    if let Some(c) = ch.as_deref_mut() {
+                        c.terminate();
+                    }
+                }
+                return;
+            }
+        };
+    }
+}
+
+/// One attach handshake: create-once, (re)join, subscribe-once, ack,
+/// drain. On a drain failure the undelivered tail stays in `buffer`
+/// for the next attach.
+#[allow(clippy::too_many_arguments)]
+fn attach<P: Encode + Decode + Send + Sync + 'static>(
+    factory: &Arc<dyn ChannelFactory<P>>,
+    ch: &mut Option<Box<dyn Channel<P>>>,
+    joined: &mut bool,
+    bus_rx: &mut Option<Receiver<Arc<Broadcast<P>>>>,
+    buffer: &mut VecDeque<Arc<Broadcast<P>>>,
+    socket: &mut ChannelSocket<P>,
+    reference: Option<String>,
+    payload: P,
+    inbound: Receiver<In<P>>,
+) -> Step<P> {
+    if ch.is_none() {
+        *ch = Some(factory.create(&socket.topic));
+    }
+    let c = ch.as_deref_mut().expect("just created");
+
+    socket.set_ref(reference);
+    let topic = socket.topic.clone();
+    match c.join(&topic, payload, socket) {
+        Ok(reply) => {
+            if bus_rx.is_none() {
+                // First successful join: subscribe BEFORE the ok reply
+                // (subscribe is a call — once the client sees its ack,
+                // membership is a fact, not a race). Once per session:
+                // the subscription is actor-scoped, survives detach,
+                // and that survival IS the buffering path.
+                match socket.bus.subscribe(&topic) {
+                    Ok(rx) => *bus_rx = Some(rx),
+                    Err(_) => {
+                        socket.send_reply(Status::Error, None);
+                        socket.set_ref(None);
+                        return Step::Exit;
+                    }
+                }
+            }
+            *joined = true;
+            socket.send_reply(Status::Ok, Some(&reply));
+            socket.set_ref(None);
+            // Drain with the NEW join generation's ref; buffered pushes
+            // have no request to correlate to (reference: None).
+            while let Some(b) = buffer.front() {
+                let out = P::encode(FrameRef {
+                    join_ref: socket.join_ref.as_deref(),
+                    reference: None,
+                    topic: &socket.topic,
+                    message: MessageRef::Event { event: &b.event, payload: Some(&b.payload) },
+                });
+                if socket.ws.send(out).is_ok() {
+                    buffer.pop_front();
+                } else {
+                    return Step::Detached;
+                }
+            }
+            Step::Attached { inbound }
+        }
+        Err(reply) => {
+            // Rejected (re)join = session over, by decision: error
+            // reply, terminate (in run_session, iff it ever joined),
+            // exit. Next join is a cold start.
+            socket.send_reply(Status::Error, Some(&reply));
+            socket.set_ref(None);
+            Step::Exit
+        }
+    }
+}
+
+fn attached_loop<P: Encode + Decode + Send + Sync + 'static>(
+    ch: &mut dyn Channel<P>,
+    socket: &ChannelSocket<P>,
+    ctl: &Receiver<Ctl<P>>,
+    inbound: &Receiver<In<P>>,
+    bus_rx: &Receiver<Arc<Broadcast<P>>>,
+    buffer: &mut VecDeque<Arc<Broadcast<P>>>,
+) -> Step<P> {
+    // ctl sits at lowest priority: it only ever carries an eviction by
+    // a second transport (rare) or the closed-arm shutdown signal. A
+    // closed arm stays ready forever, but every closed observation
+    // exits the loop immediately — no spin, no starvation window.
+    loop {
+        match smarm::select(&[inbound, bus_rx, ctl]) {
+            0 => match inbound.try_recv() {
+                Ok(Some(In::Event { reference, event, payload })) => {
+                    socket.set_ref(reference);
+                    ch.handle_in(&event, payload, socket);
+                    socket.set_ref(None);
+                }
+                Ok(Some(In::Leave { reference })) => {
+                    // Explicit leave ends the SESSION, not just the
+                    // attachment: ok reply, close event, terminate.
+                    socket.set_ref(reference);
+                    socket.send_reply(Status::Ok, None);
+                    socket.set_ref(None);
+                    close_event(socket);
+                    return Step::Exit;
+                }
+                Ok(None) => {}
+                // Conn actor finished or replaced this join generation:
+                // the transport is gone, the session is not.
+                Err(_) => return Step::Detached,
+            },
+            1 => match bus_rx.try_recv() {
+                Ok(Some(b)) => {
+                    let out = P::encode(FrameRef {
+                        join_ref: socket.join_ref.as_deref(),
+                        reference: None,
+                        topic: &socket.topic,
+                        message: MessageRef::Event { event: &b.event, payload: Some(&b.payload) },
+                    });
+                    if socket.ws.send(out).is_err() {
+                        // Transport died under us: this broadcast is
+                        // the buffer's first entry, nothing was lost.
+                        buffer.push_back(b);
+                        return Step::Detached;
+                    }
+                }
+                Ok(None) => {}
+                // The topic relay died: pubsub is gone, session over.
+                Err(_) => return Step::Exit,
+            },
+            2 => match ctl.try_recv() {
+                Ok(Some(Ctl::Attach { hs, inbound })) => {
+                    // A second transport claims the session key: evict
+                    // this one (best effort — it may already be dead)
+                    // and hand the session over.
+                    close_event(socket);
+                    return Step::Attach { hs, inbound };
+                }
+                Ok(None) => {}
+                // Registry gone = shutdown chain: terminate and exit.
+                Err(_) => return Step::Exit,
+            },
+            _ => unreachable!("three arms"),
+        }
+    }
+}
+
+fn detached_loop<P: Encode + Decode + Send + Sync + 'static>(
+    ctl: &Receiver<Ctl<P>>,
+    bus_rx: &Receiver<Arc<Broadcast<P>>>,
+    buffer: &mut VecDeque<Arc<Broadcast<P>>>,
+    cap: usize,
+    ttl: Duration,
+) -> Step<P> {
+    // TTL is per detach episode: the clock starts now, every time.
+    let deadline = Instant::now() + ttl;
+    loop {
+        // cap.max(1): a cap of 0 means "no buffering tolerated" — the
+        // first buffered broadcast tears the session down; an empty
+        // buffer still waits out the TTL.
+        if buffer.len() >= cap.max(1) {
+            return Step::Exit;
+        }
+        let remaining = deadline.saturating_duration_since(Instant::now());
+        match smarm::select_timeout(&[ctl, bus_rx], remaining) {
+            // TTL expired with no rejoin: session over.
+            None => return Step::Exit,
+            Some(0) => match ctl.try_recv() {
+                Ok(Some(Ctl::Attach { hs, inbound })) => return Step::Attach { hs, inbound },
+                Ok(None) => {}
+                Err(_) => return Step::Exit,
+            },
+            Some(1) => match bus_rx.try_recv() {
+                Ok(Some(b)) => buffer.push_back(b),
+                Ok(None) => {}
+                Err(_) => return Step::Exit,
+            },
+            Some(_) => unreachable!("two arms"),
+        }
+    }
+}
+
+/// Best-effort `phx_close` push for the socket's current join
+/// generation.
+fn close_event<P: Encode + Decode + Send + Sync + 'static>(socket: &ChannelSocket<P>) {
+    let _ = socket.ws.send(P::encode(FrameRef {
+        join_ref: socket.join_ref.as_deref(),
+        reference: None,
+        topic: &socket.topic,
+        message: MessageRef::Event { event: EV_CLOSE, payload: None },
+    }));
+}
+
+// ---------------------------------------------------------------------------
+// Tests — runtime-backed, on the toy pipe codec from testkit. The
+// session-config types (`Cfg*`) are deliberately separate from the
+// channel they configure: `channel_session::<S>` only needs `S` for
+// keying/cap/ttl, the factory builds the channel.
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::super::testkit::{eventually, Harness, TP};
+    use super::super::*;
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Mutex;
+    use std::time::Duration;
+
+    /// Counts its joins (cold start replies `joined:1`); flags
+    /// terminate; broadcasts on "shout".
+    struct Counter {
+        joins: u32,
+        term: Arc<AtomicBool>,
+        reject_rejoin: bool,
+    }
+
+    impl Channel<TP> for Counter {
+        fn join(&mut self, _topic: &str, _payload: TP, _s: &ChannelSocket<TP>) -> Result<TP, TP> {
+            self.joins += 1;
+            if self.reject_rejoin && self.joins > 1 {
+                return Err(TP("not again".into()));
+            }
+            Ok(TP(format!("joined:{}", self.joins)))
+        }
+        fn handle_in(&mut self, event: &str, payload: TP, s: &ChannelSocket<TP>) {
+            match event {
+                "shout" => s.broadcast("news", payload),
+                _ => s.reply(Status::Ok, TP(format!("echo:{}", payload.0))),
+            }
+        }
+        fn terminate(&mut self) {
+            self.term.store(true, Ordering::SeqCst);
+        }
+    }
+
+    fn counter_factory(term: &Arc<AtomicBool>, reject_rejoin: bool) -> impl ChannelFactory<TP> {
+        let term = term.clone();
+        move |_t: &str| -> Box<dyn Channel<TP>> {
+            Box::new(Counter { joins: 0, term: term.clone(), reject_rejoin })
+        }
+    }
+
+    /// Session config: keyed by topic alone, defaults otherwise.
+    struct Cfg;
+    impl ChannelSession<TP> for Cfg {
+        type Key = String;
+        fn session_key(topic: &str, _p: &TP) -> String {
+            topic.to_owned()
+        }
+    }
+
+    /// Tiny TTL (50ms) for the expiry test.
+    struct CfgTtl;
+    impl ChannelSession<TP> for CfgTtl {
+        type Key = String;
+        fn session_key(topic: &str, _p: &TP) -> String {
+            topic.to_owned()
+        }
+        fn ttl() -> Duration {
+            Duration::from_millis(50)
+        }
+    }
+
+    /// Cap of 2 (and a long TTL so only the cap can fire).
+    struct CfgCap;
+    impl ChannelSession<TP> for CfgCap {
+        type Key = String;
+        fn session_key(topic: &str, _p: &TP) -> String {
+            topic.to_owned()
+        }
+        fn buffer_cap() -> usize {
+            2
+        }
+        fn ttl() -> Duration {
+            Duration::from_secs(30)
+        }
+    }
+
+    fn session_hub<S: ChannelSession<TP, Key = String>>(
+        term: &Arc<AtomicBool>,
+        reject_rejoin: bool,
+    ) -> ChannelHub<TP> {
+        ChannelHub::new(
+            PrefixRouter::new()
+                .channel_session::<S>("room:*", counter_factory(term, reject_rejoin)),
+        )
+    }
+
+    #[test]
+    fn session_buffers_across_reconnect_and_drains_in_order() {
+        let out = Arc::new(Mutex::new(Vec::<String>::new()));
+        let (out2, term) = (out.clone(), Arc::new(AtomicBool::new(false)));
+        smarm::run(move || {
+            let hub = session_hub::<Cfg>(&term, false);
+            let mut h1 = Harness::new(&hub);
+            h1.send("j1|r1|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h1.recv());
+
+            // Transport dies. Whether the actor has observed the detach
+            // yet or not, both paths (closed inbound arm, failed ws
+            // send) land the broadcasts in the buffer.
+            drop(h1);
+            hub.broadcast("room:a", "news", TP("one".into()));
+            hub.broadcast("room:a", "news", TP("two".into()));
+
+            let mut h2 = Harness::new(&hub);
+            h2.send("j2|r2|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h2.recv()); // warm rejoin ack
+            out2.lock().unwrap().push(h2.recv()); // drained, in order
+            out2.lock().unwrap().push(h2.recv());
+        });
+        let out = out.lock().unwrap();
+        assert_eq!(out[0], "j1|r1|room:a|reply|ok|joined:1");
+        assert_eq!(out[1], "j2|r2|room:a|reply|ok|joined:2");
+        assert_eq!(out[2], "j2|-|room:a|event|news|one");
+        assert_eq!(out[3], "j2|-|room:a|event|news|two");
+    }
+
+    #[test]
+    fn session_ttl_expiry_tears_down_then_cold_start() {
+        let out = Arc::new(Mutex::new(Vec::<String>::new()));
+        let (out2, term) = (out.clone(), Arc::new(AtomicBool::new(false)));
+        let term2 = term.clone();
+        smarm::run(move || {
+            let hub = session_hub::<CfgTtl>(&term2, false);
+            let mut h1 = Harness::new(&hub);
+            h1.send("j1|r1|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h1.recv());
+            drop(h1);
+            assert!(eventually(|| term2.load(Ordering::SeqCst)), "ttl never fired");
+
+            let mut h2 = Harness::new(&hub);
+            h2.send("j2|r2|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h2.recv());
+        });
+        let out = out.lock().unwrap();
+        assert_eq!(out[0], "j1|r1|room:a|reply|ok|joined:1");
+        assert_eq!(out[1], "j2|r2|room:a|reply|ok|joined:1"); // cold
+    }
+
+    #[test]
+    fn session_buffer_cap_tears_down_then_cold_start() {
+        let out = Arc::new(Mutex::new(Vec::<String>::new()));
+        let (out2, term) = (out.clone(), Arc::new(AtomicBool::new(false)));
+        smarm::run(move || {
+            let hub = session_hub::<CfgCap>(&term, false);
+            let mut h1 = Harness::new(&hub);
+            h1.send("j1|r1|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h1.recv());
+            drop(h1);
+            // Cap is 2: the second buffered broadcast tears it down
+            // (ttl is 30s — only the cap can fire here).
+            hub.broadcast("room:a", "news", TP("one".into()));
+            hub.broadcast("room:a", "news", TP("two".into()));
+            assert!(eventually(|| term.load(Ordering::SeqCst)), "cap never fired");
+
+            let mut h2 = Harness::new(&hub);
+            h2.send("j2|r2|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h2.recv());
+        });
+        let out = out.lock().unwrap();
+        assert_eq!(out[0], "j1|r1|room:a|reply|ok|joined:1");
+        assert_eq!(out[1], "j2|r2|room:a|reply|ok|joined:1"); // cold
+    }
+
+    #[test]
+    fn leave_ends_the_session_not_just_the_attachment() {
+        let out = Arc::new(Mutex::new(Vec::<String>::new()));
+        let (out2, term) = (out.clone(), Arc::new(AtomicBool::new(false)));
+        smarm::run(move || {
+            let hub = session_hub::<Cfg>(&term, false);
+            let mut h = Harness::new(&hub);
+            h.send("j1|r1|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h.recv());
+            h.send("j1|r2|room:a|event|phx_leave|");
+            out2.lock().unwrap().push(h.recv()); // ok reply
+            out2.lock().unwrap().push(h.recv()); // phx_close
+            assert!(eventually(|| term.load(Ordering::SeqCst)), "leave never terminated");
+
+            h.send("j2|r3|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h.recv());
+        });
+        let out = out.lock().unwrap();
+        assert_eq!(out[0], "j1|r1|room:a|reply|ok|joined:1");
+        assert_eq!(out[1], "j1|r2|room:a|reply|ok|");
+        assert_eq!(out[2], "j1|-|room:a|event|phx_close|");
+        assert_eq!(out[3], "j2|r3|room:a|reply|ok|joined:1"); // cold
+    }
+
+    #[test]
+    fn second_transport_evicts_first() {
+        let out = Arc::new(Mutex::new(Vec::<String>::new()));
+        let (out2, term) = (out.clone(), Arc::new(AtomicBool::new(false)));
+        smarm::run(move || {
+            let hub = session_hub::<Cfg>(&term, false);
+            let mut h1 = Harness::new(&hub);
+            h1.send("j1|r1|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h1.recv());
+
+            let mut h2 = Harness::new(&hub);
+            h2.send("j2|r2|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h2.recv()); // warm handover ack
+            out2.lock().unwrap().push(h1.recv()); // eviction phx_close
+
+            hub.broadcast("room:a", "news", TP("x".into()));
+            out2.lock().unwrap().push(h2.recv()); // only h2 is attached
+            h1.assert_silence();
+
+            // h1's conn-side entry is stale: its inbound receiver was
+            // dropped on eviction, so the next event self-prunes with
+            // an error reply.
+            h1.send("j1|r3|room:a|event|ping|x");
+            out2.lock().unwrap().push(h1.recv());
+        });
+        let out = out.lock().unwrap();
+        assert_eq!(out[0], "j1|r1|room:a|reply|ok|joined:1");
+        assert_eq!(out[1], "j2|r2|room:a|reply|ok|joined:2");
+        assert_eq!(out[2], "j1|-|room:a|event|phx_close|");
+        assert_eq!(out[3], "j2|-|room:a|event|news|x");
+        assert_eq!(out[4], "j1|r3|room:a|reply|error|");
+    }
+
+    #[test]
+    fn rejected_rejoin_ends_the_session() {
+        let out = Arc::new(Mutex::new(Vec::<String>::new()));
+        let (out2, term) = (out.clone(), Arc::new(AtomicBool::new(false)));
+        smarm::run(move || {
+            let hub = session_hub::<Cfg>(&term, true);
+            let mut h1 = Harness::new(&hub);
+            h1.send("j1|r1|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h1.recv());
+            drop(h1);
+
+            let mut h2 = Harness::new(&hub);
+            h2.send("j2|r2|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h2.recv()); // rejoin rejected
+            assert!(eventually(|| term.load(Ordering::SeqCst)), "reject never terminated");
+
+            let mut h3 = Harness::new(&hub);
+            h3.send("j3|r3|room:a|event|phx_join|u");
+            out2.lock().unwrap().push(h3.recv()); // cold start
+        });
+        let out = out.lock().unwrap();
+        assert_eq!(out[0], "j1|r1|room:a|reply|ok|joined:1");
+        assert_eq!(out[1], "j2|r2|room:a|reply|error|not again");
+        assert_eq!(out[2], "j3|r3|room:a|reply|ok|joined:1");
+    }
+}

src/channels/testkit.rs

@@ -0,0 +1,121 @@
+//! Shared test scaffolding for the channels module tree: the toy
+//! pipe-delimited codec (`TP`) and the conn-side `Harness` that fakes a
+//! websocket transport. `cfg(test)` only.
+
+use super::*;
+use crate::ws::duplex::Outbound;
+use std::time::Duration;
+
+/// Toy payload + codec: `jref|ref|topic|kind|event-or-status|payload`
+/// with `-` for absent refs. Enough to drive the machinery.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) struct TP(pub(crate) String);
+
+pub(crate) fn part(o: Option<&str>) -> &str {
+    o.unwrap_or("-")
+}
+
+impl Encode for TP {
+    fn encode(f: FrameRef<'_, Self>) -> Message {
+        let s = match f.message {
+            MessageRef::Event { event, payload } => format!(
+                "{}|{}|{}|event|{}|{}",
+                part(f.join_ref),
+                part(f.reference),
+                f.topic,
+                event,
+                payload.map(|p| p.0.as_str()).unwrap_or("")
+            ),
+            MessageRef::Reply { status, payload } => format!(
+                "{}|{}|{}|reply|{}|{}",
+                part(f.join_ref),
+                part(f.reference),
+                f.topic,
+                match status {
+                    Status::Ok => "ok",
+                    Status::Error => "error",
+                },
+                payload.map(|p| p.0.as_str()).unwrap_or("")
+            ),
+        };
+        Message::Text(s)
+    }
+}
+
+impl Decode for TP {
+    fn decode(msg: &Message) -> Result<ChannelFrame<Self>, DecodeError> {
+        let Message::Text(s) = msg else {
+            return Err(DecodeError("binary".into()));
+        };
+        let p: Vec<&str> = s.splitn(6, '|').collect();
+        if p.len() != 6 || p[3] != "event" {
+            return Err(DecodeError(format!("bad frame: {s}")));
+        }
+        let opt = |x: &str| (x != "-").then(|| x.to_string());
+        Ok(ChannelFrame {
+            join_ref: opt(p[0]),
+            reference: opt(p[1]),
+            topic: p[2].to_string(),
+            message: ChannelMessage::Event { event: p[4].to_string(), payload: TP(p[5].into()) },
+        })
+    }
+}
+
+/// A fake socket: the conn-side handler plus the raw Outbound channel
+/// a real duplex loop would drain. `recv_text` pulls the next encoded
+/// frame the "client" would see.
+pub(crate) struct Harness {
+    handler: SocketHandler<TP>,
+    sender: WsSender,
+    out_rx: smarm::Receiver<Outbound>,
+}
+
+impl Harness {
+    pub(crate) fn new(hub: &ChannelHub<TP>) -> Self {
+        let (tx, out_rx) = smarm::channel();
+        Self {
+            handler: SocketHandler {
+                bus: hub.bus.clone(),
+                router: hub.router.clone(),
+                joined: HashMap::new(),
+            },
+            sender: WsSender { tx },
+            out_rx,
+        }
+    }
+
+    /// Feed one wire line in, as the duplex loop would.
+    pub(crate) fn send(&mut self, line: &str) {
+        self.handler
+            .on_message(Message::Text(line.to_string()), &self.sender.clone());
+    }
+
+    /// Assert nothing arrives for this client within a short window —
+    /// for "the broadcast must NOT reach the evicted transport" cases.
+    pub(crate) fn assert_silence(&self) {
+        if let Ok(Outbound::Msg(Message::Text(s))) =
+            self.out_rx.recv_timeout(Duration::from_millis(100))
+        {
+            panic!("expected silence, got frame: {s}");
+        }
+    }
+
+    /// Next encoded frame the client would see (2s budget — channel
+    /// actors answer asynchronously).
+    pub(crate) fn recv(&self) -> String {
+        match self.out_rx.recv_timeout(Duration::from_secs(2)) {
+            Ok(Outbound::Msg(Message::Text(s))) => s,
+            other => panic!("expected outbound text frame, got {:?}", other.is_ok()),
+        }
+    }
+}
+
+pub(crate) fn eventually(mut f: impl FnMut() -> bool) -> bool {
+    for _ in 0..200 {
+        if f() {
+            return true;
+        }
+        smarm::sleep(Duration::from_millis(10));
+    }
+    false
+}

src/conn.rs

@@ -146,21 +146,73 @@ impl Body {
 // RespBody — what plugs put on the wire.
 // ---------------------------------------------------------------------------
 //
-// Enum, not a trait, so the connection actor can pattern-match. Leaves room
-// for future variants like Sse, Stream, Chunked without touching the plug
-// API.
+// Enum, not a trait, so the connection actor can pattern-match.
+//
+// `Stream` is the pull-shaped streaming body (v0.3 design decision): the
+// handler hands back a `smarm::Receiver<Vec<u8>>` — typically the read end
+// of a channel whose `Sender` lives in a producer actor the handler
+// spawned — and the connection actor pumps it onto the wire. The conn
+// actor keeps sole ownership of the socket and of write deadlines; the
+// producer never touches the fd. End-of-stream is signalled by dropping
+// every `Sender` (the conn actor then emits the terminating 0-chunk).
+// Empty `Vec`s are skipped by the pump (a zero-length chunk would
+// terminate chunked framing early), so they are safe to send but useless.
 
-#[derive(Debug, Clone)]
 pub enum RespBody {
     Empty,
     Bytes(Vec<u8>),
+    Stream(StreamBody),
+}
+
+/// A streaming response body. Construct with [`StreamBody::new`] (or
+/// `RespBody::from(rx)`) and hand it to [`Conn::put_body`].
+///
+/// On HTTP/1.1 the connection actor sends it with
+/// `Transfer-Encoding: chunked` and the connection stays reusable after
+/// the stream completes. On HTTP/1.0 (no chunked framing) the bytes are
+/// written raw and the connection closes at end of stream to delimit the
+/// body.
+pub struct StreamBody {
+    pub rx: smarm::Receiver<Vec<u8>>,
+    /// If set, the connection actor's pump waits for each chunk with
+    /// `recv_timeout(interval)` instead of a bare `recv`, and on expiry
+    /// writes `payload` as its own chunk and keeps waiting. This is how
+    /// SSE keep-alive comments work: liveness comes from the ping (a dead
+    /// client is detected when a heartbeat write stalls past
+    /// `write_timeout`), not from any request clock.
+    pub heartbeat: Option<(std::time::Duration, Vec<u8>)>,
+}
+
+impl StreamBody {
+    pub fn new(rx: smarm::Receiver<Vec<u8>>) -> Self {
+        Self { rx, heartbeat: None }
+    }
+
+    pub fn with_heartbeat(mut self, interval: std::time::Duration, payload: Vec<u8>) -> Self {
+        self.heartbeat = Some((interval, payload));
+        self
+    }
+}
+
+impl std::fmt::Debug for RespBody {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            RespBody::Empty     => f.write_str("Empty"),
+            RespBody::Bytes(b)  => f.debug_tuple("Bytes").field(&b.len()).finish(),
+            RespBody::Stream(_) => f.write_str("Stream(..)"),
+        }
+    }
 }
 
 impl RespBody {
+    /// Body length for fixed bodies; 0 for `Stream` (a stream has no
+    /// length up front — that is the point — and is never serialised with
+    /// a `content-length`).
     pub fn len_hint(&self) -> usize {
         match self {
             RespBody::Empty     => 0,
             RespBody::Bytes(b)  => b.len(),
+            RespBody::Stream(_) => 0,
         }
     }
 }
@@ -256,6 +308,11 @@ pub struct Conn {
     pub params:  Params,
     pub assigns: Assigns,
     pub halted:  bool,
+
+    /// Set by [`Conn::upgrade`] on an accepted WebSocket handshake; the
+    /// connection actor sees it (with status 101) and leaves the HTTP
+    /// loop after writing the response. `None` for plain HTTP.
+    pub upgrade: Option<crate::ws::WsUpgrade>,
 }
 
 impl Conn {
@@ -277,6 +334,8 @@ impl Conn {
             params:  Params::new(),
             assigns: Assigns::new(),
             halted:  false,
+
+            upgrade: None,
         }
     }
 
@@ -306,6 +365,52 @@ impl Conn {
         self.halted = true;
         self
     }
+
+    /// Accept a WebSocket upgrade on this request (RFC 6455 §4.2),
+    /// handing `handler` to the duplex loop that takes the socket over.
+    ///
+    /// On a valid handshake: status `101`, the `upgrade`/`connection`/
+    /// `sec-websocket-accept` response headers, the [`WsUpgrade`] payload
+    /// the connection actor acts on, and the pipeline is halted. After
+    /// the 101 the connection actor leaves HTTP and drives `handler` —
+    /// see [`WsHandler`](crate::ws::WsHandler) for the callback contract.
+    ///
+    /// On an invalid handshake: `handler` is dropped untouched and the
+    /// appropriate rejection goes out (`400`, or `426` +
+    /// `sec-websocket-version: 13` for a version mismatch), empty body,
+    /// pipeline halted; the connection stays plain HTTP with normal
+    /// keep-alive semantics. Pre-check with
+    /// [`ws::handshake::is_upgrade_request`](crate::ws::handshake::is_upgrade_request)
+    /// to branch before committing.
+    ///
+    /// [`WsUpgrade`]: crate::ws::WsUpgrade
+    pub fn upgrade(mut self, handler: impl crate::ws::WsHandler) -> Self {
+        use crate::ws::{handshake, Rejection};
+        match handshake::validate(&self) {
+            Ok(accept) => {
+                self.upgrade = Some(crate::ws::WsUpgrade {
+                    handler: Box::new(handler),
+                });
+                self.put_status(101)
+                    .put_header("upgrade", "websocket")
+                    .put_header("connection", "Upgrade")
+                    .put_header("sec-websocket-accept", accept)
+                    .put_body(RespBody::Empty)
+                    .halt()
+            }
+            Err(rej) => {
+                let c = self
+                    .put_status(rej.status())
+                    .put_body(RespBody::Empty)
+                    .halt();
+                if rej == Rejection::UnsupportedVersion {
+                    c.put_header("sec-websocket-version", "13")
+                } else {
+                    c
+                }
+            }
+        }
+    }
 }
 
 impl Default for Conn {
@@ -326,3 +431,11 @@ impl From<&'static str> for RespBody {
 impl From<&[u8]> for RespBody {
     fn from(s: &[u8]) -> Self { RespBody::Bytes(s.to_vec()) }
 }
+impl From<StreamBody> for RespBody {
+    fn from(s: StreamBody) -> Self { RespBody::Stream(s) }
+}
+impl From<smarm::Receiver<Vec<u8>>> for RespBody {
+    fn from(rx: smarm::Receiver<Vec<u8>>) -> Self {
+        RespBody::Stream(StreamBody::new(rx))
+    }
+}

src/conn_actor.rs

@@ -13,14 +13,17 @@
 //! `wait_readable` between bytes and `wait_writable` during slow writes;
 //! during those parks, other connection actors progress freely.
 
-use crate::conn::{Body, Conn, RespBody};
+use crate::conn::{Body, Conn, HttpVersion, RespBody, StreamBody};
+use crate::conn_registry::{Cast, ConnRegistry, DeregisterGuard};
 use crate::net::OwnedFd;
 use crate::parser::{self, ParseError};
 use crate::plug::Pipeline;
 
+use smarm::ServerRef;
+
 use std::io::{self, ErrorKind};
 use std::os::fd::RawFd;
-use std::time::Duration;
+use std::time::{Duration, Instant};
 
 // ---------------------------------------------------------------------------
 // Limits
@@ -38,7 +41,31 @@ pub struct ConnLimits {
     /// Hard cap on Content-Length we'll accept. 16 MiB is enough for a CRUD
     /// example; configurable in `Config`.
     pub max_body_bytes:     usize,
+    /// Idle budget between requests: how long we'll park waiting for the
+    /// FIRST byte of a request (including the first request on a fresh
+    /// connection). Expiry closes the connection silently — nothing is
+    /// owed to a client that isn't talking.
     pub keep_alive_timeout: Duration,
+    /// Per-request wall-clock budget, measured from the first byte of a
+    /// request until the request (head + body) is fully read. Expiry
+    /// mid-head gets a best-effort 408; expiry mid-body just closes.
+    /// Pipeline run time is NOT covered — that's the handler's business.
+    /// Covers the READ phase only; the write phase has its own
+    /// per-write budget (`write_timeout`) so a streaming response can
+    /// legitimately outlive any whole-request clock.
+    pub request_timeout:    Duration,
+    /// Per-write budget for response bytes: every `write_all` (the fixed
+    /// head+body, and each streamed chunk) must complete within this.
+    /// A client that stops reading mid-response is dropped when its
+    /// socket buffer fills and a write stalls past the budget.
+    pub write_timeout:      Duration,
+    /// WebSocket: hard cap on a single frame's payload, enforced from
+    /// the frame header BEFORE the payload is buffered. Violation closes
+    /// with 1009.
+    pub max_frame_payload:  usize,
+    /// WebSocket: hard cap on a complete (reassembled) message; spans
+    /// fragments. Violation closes with 1009.
+    pub max_message_bytes:  usize,
 }
 
 impl Default for ConnLimits {
@@ -49,6 +76,10 @@ impl Default for ConnLimits {
             max_head_bytes:     64 * 1024,
             max_body_bytes:     16 * 1024 * 1024,
             keep_alive_timeout: Duration::from_secs(60),
+            request_timeout:    Duration::from_secs(30),
+            write_timeout:      Duration::from_secs(30),
+            max_frame_payload:  1024 * 1024,
+            max_message_bytes:  4 * 1024 * 1024,
         }
     }
 }
@@ -57,34 +88,69 @@ impl Default for ConnLimits {
 // run_connection — entry point spawned by the listener actor.
 // ---------------------------------------------------------------------------
 
-pub fn run_connection(fd: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
+pub fn run_connection(
+    fd: OwnedFd,
+    pipeline: Pipeline,
+    limits: ConnLimits,
+    registry: ServerRef<ConnRegistry>,
+) {
     // The OwnedFd cleans up via Drop on any exit path (panic, error, or
     // normal close). No explicit close calls below.
     let raw = fd.as_raw();
     let mut buf: Vec<u8> = Vec::with_capacity(limits.initial_read_buf);
 
+    // Self-register (initially idle: no request head parsed yet) and arm
+    // the deregistration guard. Both casts come from this actor, so
+    // Started always precedes Ended in the registry's inbox — see
+    // conn_registry module docs for why the listener must not do this.
+    let me = smarm::self_pid();
+    let _ = registry.cast(Cast::ConnStarted(me));
+    let _guard = DeregisterGuard::new(registry.clone(), me, Cast::ConnEnded);
+
     loop {
         // ----- 1. Read until we have a full request head. -----
-        let parsed = match read_head(raw, &mut buf, &limits) {
+        // We are idle until a head parses: stoppable by a draining
+        // registry while parked here.
+        let (parsed, request_deadline) = match read_head(raw, &mut buf, &limits) {
             Ok(p) => p,
             Err(ReadHeadErr::ClientClosed) => {
                 // Clean EOF between requests (or before any request). Normal.
                 return;
             }
+            Err(ReadHeadErr::IdleTimeout) => {
+                // keep_alive_timeout expired waiting for the first byte of
+                // a request. Nothing is owed; close silently.
+                return;
+            }
+            Err(ReadHeadErr::RequestTimeout) => {
+                // request_timeout expired mid-head (slowloris and friends).
+                // Best-effort 408 WITHOUT parking on writability — a client
+                // that stalls reads must not defeat the timeout by making
+                // the 408 write park forever.
+                try_write_once(raw, b"HTTP/1.1 408 Request Timeout\r\ncontent-length: 0\r\nconnection: close\r\n\r\n");
+                return;
+            }
             Err(ReadHeadErr::Io(_)) => {
-                // Network error or timeout. Best-effort close; we're done.
+                // Network error. Best-effort close; we're done.
                 return;
             }
             Err(ReadHeadErr::Parse(e)) => {
-                emit_error_response(raw, &e);
+                emit_error_response(raw, &e, Instant::now() + limits.write_timeout);
                 return;
             }
         };
+        let _ = registry.cast(Cast::ConnBusy(me));
 
         // ----- 2. Read body. -----
+        // Content-Length pre-check only applies to fixed bodies; a chunked
+        // body is bounded incrementally by the decoder.
         let body_len = parsed.content_length.unwrap_or(0);
         if body_len > limits.max_body_bytes {
-            let _ = write_all(raw, b"HTTP/1.1 413 Payload Too Large\r\ncontent-length: 0\r\nconnection: close\r\n\r\n");
+            let _ = write_all(
+                raw,
+                b"HTTP/1.1 413 Payload Too Large\r\ncontent-length: 0\r\nconnection: close\r\n\r\n",
+                Instant::now() + limits.write_timeout,
+            );
             return;
         }
 
@@ -92,14 +158,46 @@ pub fn run_connection(fd: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
         // body. RFC 7231 §5.1.1. We don't gate on app logic here; v1 always
         // accepts.
         if parsed.expect_100 {
-            if write_all(raw, b"HTTP/1.1 100 Continue\r\n\r\n").is_err() {
+            if write_all(raw, b"HTTP/1.1 100 Continue\r\n\r\n", Instant::now() + limits.write_timeout).is_err() {
                 return;
             }
         }
 
-        let body = match read_body(raw, &mut buf, parsed.head_len, body_len) {
-            Ok(b) => b,
+        // `consumed_past_head`: how many RAW bytes of `buf` past the head
+        // this request's body occupied — for chunked bodies that is framing
+        // included, NOT the decoded length. The keep-alive drain at the
+        // bottom of the loop must drop exactly this much to land on the
+        // next pipelined request.
+        let (body, consumed_past_head) = if parsed.chunked {
+            match read_chunked_body(raw, &mut buf, parsed.head_len, &limits, request_deadline) {
+                Ok(ok) => ok,
+                Err(ChunkedBodyErr::TooLarge) => {
+                    let _ = write_all(
+                        raw,
+                        b"HTTP/1.1 413 Payload Too Large\r\ncontent-length: 0\r\nconnection: close\r\n\r\n",
+                        Instant::now() + limits.write_timeout,
+                    );
+                    return;
+                }
+                Err(ChunkedBodyErr::Malformed) => {
+                    let _ = write_all(
+                        raw,
+                        b"HTTP/1.1 400 Bad Request\r\ncontent-length: 0\r\nconnection: close\r\n\r\n",
+                        Instant::now() + limits.write_timeout,
+                    );
+                    return;
+                }
+                // Timeout mid-body (and any other io error) -> just close.
+                Err(ChunkedBodyErr::Io(_)) => return,
+            }
+        } else {
+            match read_body(raw, &mut buf, parsed.head_len, body_len, request_deadline) {
+                Ok(b) => (b, body_len),
+                // Timeout mid-body (and any other body io error) -> just
+                // close; there's no point talking HTTP to a client this far
+                // gone.
                 Err(_) => return,
+            }
         };
 
         let keep_alive = parsed.keep_alive;
@@ -117,6 +215,16 @@ pub fn run_connection(fd: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
         let mut response_conn = match result {
             Ok(c)  => c,
             Err(_) => {
+                // Distinguish a genuine handler panic from smarm's stop
+                // sentinel, which is also a panic payload and which this
+                // catch_unwind would otherwise swallow — turning a
+                // graceful stop into a 500-and-keep-running. The stop
+                // flag is persistent (not consumed by raising the
+                // sentinel), so if we were stopped this re-raises it
+                // here, outside the catch, and we unwind properly (the
+                // fd and registry guards clean up).
+                smarm::preempt::check_cancelled();
+
                 // Compose a 500 manually; the original Conn was moved into
                 // the closure.
                 let mut c = Conn::new();
@@ -132,20 +240,71 @@ pub fn run_connection(fd: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
                 .put_body(RespBody::Empty);
         }
 
-        // ----- 4. Write the response. -----
-        let bytes = parser::serialise_response(&response_conn, keep_alive);
-        if write_all(raw, &bytes).is_err() {
+        // ----- 3.5 WebSocket upgrade. -----
+        // An accepted handshake (payload + 101) ends HTTP on this socket:
+        // write the 101 head, hand the fd to the duplex loop with the
+        // boxed handler and any bytes already read past this request (a
+        // client may pipeline its first frame behind the handshake — those
+        // bytes are ws bytes now). The registry entry stays Busy for the
+        // whole ws lifetime: an open WebSocket is in-flight work, not
+        // reapable idle HTTP; graceful shutdown force-stops it out of the
+        // select park at the drain deadline. The status check is
+        // defensive: a post-handler plug that clobbered the 101 forfeits
+        // the upgrade and falls through to plain HTTP.
+        if response_conn.upgrade.is_some() && response_conn.status == Some(101) {
+            let head = parser::serialise_response(&response_conn, true);
+            if write_all(raw, &head, Instant::now() + limits.write_timeout).is_err() {
                 return;
             }
+            let upgrade = response_conn.upgrade.take().expect("checked above");
+            buf.drain(..head_len + consumed_past_head);
+            crate::ws::duplex::run_duplex(raw, buf, upgrade.handler, &limits);
+            return;
+        }
+
+        // ----- 4. Write the response. -----
+        // A Stream body on HTTP/1.0 has no chunked framing: the body is
+        // delimited by EOF, so keep-alive is forced off for this response
+        // (and `connection: close` goes on the wire). Error statuses on
+        // 1.0 also force close: we don't advertise keep-alive on a
+        // 4xx/5xx to a protocol generation where reuse is opt-in.
+        let is_stream = matches!(response_conn.resp_body, RespBody::Stream(_));
+        let is_error  = response_conn.status.unwrap_or(200) >= 400;
+        let keep_alive = keep_alive
+            && !(version == HttpVersion::Http10 && (is_stream || is_error));
+
+        let head_bytes = parser::serialise_response(&response_conn, keep_alive);
+        if write_all(raw, &head_bytes, Instant::now() + limits.write_timeout).is_err() {
+            return;
+        }
+
+        if let RespBody::Stream(stream) = response_conn.resp_body {
+            let chunked = version == HttpVersion::Http11;
+            if pump_stream(raw, stream, chunked, limits.write_timeout).is_err() {
+                return;
+            }
+            if !chunked {
+                // EOF delimits the HTTP/1.0 stream body.
+                return;
+            }
+        }
 
         // ----- 5. Loop or close. -----
         if !keep_alive {
             return;
         }
 
-        // Drop the request bytes (head + body) from `buf`; anything past
-        // them is the start of the next pipelined request.
-        let consumed = head_len + body_len;
+        // Response is on the wire; nothing is owed. Going idle here makes
+        // us stoppable by a draining registry while we park for the next
+        // keep-alive request. (If the next request is already pipelined in
+        // `buf`, the very next read_head parses it without parking and we
+        // go Busy again — a draining registry's request_stop may still
+        // catch us, which is acceptable: drain means no new work.)
+        let _ = registry.cast(Cast::ConnIdle(me));
+
+        // Drop the request bytes (head + raw body framing) from `buf`;
+        // anything past them is the start of the next pipelined request.
+        let consumed = head_len + consumed_past_head;
         buf.drain(..consumed);
     }
 }
@@ -157,6 +316,12 @@ pub fn run_connection(fd: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
 #[allow(dead_code)] // io::Error is captured for future logging
 enum ReadHeadErr {
     ClientClosed,
+    /// keep_alive_timeout expired while waiting for the first byte of a
+    /// request. Close silently.
+    IdleTimeout,
+    /// request_timeout expired after the request had started arriving.
+    /// Best-effort 408.
+    RequestTimeout,
     Io(io::Error),
     Parse(ParseError),
 }
@@ -164,17 +329,41 @@ enum ReadHeadErr {
 /// Read until `parse_head` succeeds or fails definitively. `buf` may already
 /// contain leftover bytes from a previous keep-alive cycle; we try to parse
 /// those before reading more from the socket.
+///
+/// Two wall-clock budgets govern the waits (each wait uses whichever budget
+/// is currently active):
+///
+/// - while `buf` is empty and nothing has arrived, we are *idle* and the
+///   wait is bounded by `keep_alive_timeout`;
+/// - the instant the request has started (first byte read, or pipelined
+///   bytes already in `buf` at entry), the *request* clock starts: an
+///   `Instant` deadline of `request_timeout` from that moment, which also
+///   covers body reads — it is returned alongside the parsed head so the
+///   caller can thread it into `read_body`.
 fn read_head(
     fd: RawFd,
     buf: &mut Vec<u8>,
     limits: &ConnLimits,
-) -> Result<parser::ParsedHead, ReadHeadErr> {
+) -> Result<(parser::ParsedHead, Instant), ReadHeadErr> {
+    let entry = Instant::now();
+    let idle_deadline = entry + limits.keep_alive_timeout;
+    // Pipelined leftovers count as a started request.
+    let mut request_deadline: Option<Instant> = if buf.is_empty() {
+        None
+    } else {
+        Some(entry + limits.request_timeout)
+    };
+
     loop {
         // Try to parse what we already have. On the first iteration of a
         // fresh keep-alive cycle, `buf` may already hold the next request.
         if !buf.is_empty() {
             match parser::parse_head(buf, limits.max_headers) {
-                Ok(h)  => return Ok(h),
+                Ok(h)  => {
+                    let deadline = request_deadline
+                        .unwrap_or_else(|| Instant::now() + limits.request_timeout);
+                    return Ok((h, deadline));
+                }
                 Err(ParseError::Incomplete) => {} // need more bytes
                 Err(e) => return Err(ReadHeadErr::Parse(e)),
             }
@@ -184,10 +373,24 @@ fn read_head(
             return Err(ReadHeadErr::Parse(ParseError::TooManyHeaders));
         }
 
-        // Read more.
-        match read_some(fd, buf, limits.initial_read_buf) {
+        // Read more, bounded by whichever budget is active.
+        let deadline = request_deadline.unwrap_or(idle_deadline);
+        match read_some(fd, buf, limits.initial_read_buf, deadline) {
             Ok(0)  => return Err(ReadHeadErr::ClientClosed),
-            Ok(_)  => continue,
+            Ok(_)  => {
+                if request_deadline.is_none() {
+                    // First byte(s) of this request: the request clock
+                    // starts now.
+                    request_deadline = Some(Instant::now() + limits.request_timeout);
+                }
+            }
+            Err(e) if e.kind() == ErrorKind::TimedOut => {
+                return Err(if request_deadline.is_some() {
+                    ReadHeadErr::RequestTimeout
+                } else {
+                    ReadHeadErr::IdleTimeout
+                });
+            }
             Err(e) => return Err(ReadHeadErr::Io(e)),
         }
     }
@@ -202,6 +405,7 @@ fn read_body(
     buf: &mut Vec<u8>,
     head_len: usize,
     body_len: usize,
+    deadline: Instant,
 ) -> io::Result<Vec<u8>> {
     // Bytes already in `buf` past the head belong to the body.
     let already = buf.len().saturating_sub(head_len);
@@ -213,10 +417,11 @@ fn read_body(
         return Ok(buf[head_len..head_len + body_len].to_vec());
     }
 
-    // Read until we have the rest.
+    // Read until we have the rest, on the same request budget that the
+    // head was read under.
     let mut total_read = already;
     while total_read < body_len {
-        match read_some(fd, buf, 8 * 1024) {
+        match read_some(fd, buf, 8 * 1024, deadline) {
             Ok(0)  => return Err(io::Error::new(ErrorKind::UnexpectedEof, "client closed during body")),
             Ok(n)  => total_read += n,
             Err(e) => return Err(e),
@@ -226,18 +431,160 @@ fn read_body(
 }
 
 // ---------------------------------------------------------------------------
-// read_some — single epoll-park + read loop.
+// read_chunked_body — incremental chunked transfer-decoding (request side).
 // ---------------------------------------------------------------------------
 //
-// Appends what it reads onto `buf`. Returns bytes read, 0 for EOF, or the
-// last io error.
+// Decodes `Transfer-Encoding: chunked` from `buf[head_len..]`, reading more
+// from the socket as needed on the SAME request deadline the head was read
+// under. Returns (decoded_body, raw_bytes_consumed_past_head) — the raw
+// count includes all framing and the trailer section, so the caller's
+// keep-alive drain lands exactly on the next pipelined request.
+//
+// Bounds: the DECODED size is capped at max_body_bytes (-> TooLarge/413);
+// a single size line (incl. chunk extensions, which are ignored) is capped
+// at MAX_SIZE_LINE and the trailer section at MAX_TRAILER_BYTES (-> 
+// Malformed/400) so framing spam can't grow `buf` unboundedly. Trailers
+// are consumed and discarded — nothing in the pipeline wants them yet.
 
-fn read_some(fd: RawFd, buf: &mut Vec<u8>, chunk: usize) -> io::Result<usize> {
+const MAX_SIZE_LINE:     usize = 128;
+const MAX_TRAILER_BYTES: usize = 8 * 1024;
+
+#[allow(dead_code)] // io::Error is captured for future logging
+enum ChunkedBodyErr {
+    Io(io::Error),
+    Malformed,
+    TooLarge,
+}
+
+fn read_chunked_body(
+    fd: RawFd,
+    buf: &mut Vec<u8>,
+    head_len: usize,
+    limits: &ConnLimits,
+    deadline: Instant,
+) -> Result<(Vec<u8>, usize), ChunkedBodyErr> {
+    // Ensure `buf` holds at least `until` bytes, reading on the request
+    // deadline. Io(TimedOut) on expiry, UnexpectedEof on early close.
+    fn fill_to(
+        fd: RawFd,
+        buf: &mut Vec<u8>,
+        until: usize,
+        deadline: Instant,
+    ) -> Result<(), ChunkedBodyErr> {
+        while buf.len() < until {
+            match read_some(fd, buf, 8 * 1024, deadline) {
+                Ok(0) => {
+                    return Err(ChunkedBodyErr::Io(io::Error::new(
+                        ErrorKind::UnexpectedEof,
+                        "client closed during chunked body",
+                    )))
+                }
+                Ok(_) => {}
+                Err(e) => return Err(ChunkedBodyErr::Io(e)),
+            }
+        }
+        Ok(())
+    }
+
+    // Find "\r\n" in buf[from..], reading more as needed; the line may be
+    // at most `max_line` bytes (terminator excluded). Returns the index of
+    // the '\r'.
+    fn find_crlf(
+        fd: RawFd,
+        buf: &mut Vec<u8>,
+        from: usize,
+        max_line: usize,
+        deadline: Instant,
+    ) -> Result<usize, ChunkedBodyErr> {
+        let mut scan = from;
+        loop {
+            while scan + 1 < buf.len() {
+                if buf[scan] == b'\r' && buf[scan + 1] == b'\n' {
+                    return Ok(scan);
+                }
+                scan += 1;
+                if scan - from > max_line {
+                    return Err(ChunkedBodyErr::Malformed);
+                }
+            }
+            fill_to(fd, buf, buf.len() + 1, deadline)?;
+        }
+    }
+
+    let mut pos = head_len;
+    let mut decoded: Vec<u8> = Vec::new();
+
+    loop {
+        // ----- size line: HEX[;extensions]\r\n -----
+        let line_end = find_crlf(fd, buf, pos, MAX_SIZE_LINE, deadline)?;
+        let line = &buf[pos..line_end];
+        let size_str = match line.iter().position(|&b| b == b';') {
+            Some(i) => &line[..i], // chunk extensions: ignored
+            None    => line,
+        };
+        let size_str = std::str::from_utf8(size_str)
+            .map_err(|_| ChunkedBodyErr::Malformed)?
+            .trim();
+        let size = usize::from_str_radix(size_str, 16)
+            .map_err(|_| ChunkedBodyErr::Malformed)?;
+        pos = line_end + 2;
+
+        if size == 0 {
+            // ----- trailer section: zero or more header lines, then CRLF -----
+            let trailer_start = pos;
+            loop {
+                let t_end = find_crlf(fd, buf, pos, MAX_SIZE_LINE.max(1024), deadline)?;
+                let empty = t_end == pos;
+                pos = t_end + 2;
+                if empty {
+                    return Ok((decoded, pos - head_len));
+                }
+                if pos - trailer_start > MAX_TRAILER_BYTES {
+                    return Err(ChunkedBodyErr::Malformed);
+                }
+            }
+        }
+
+        if decoded.len() + size > limits.max_body_bytes {
+            return Err(ChunkedBodyErr::TooLarge);
+        }
+
+        // ----- chunk payload + trailing CRLF -----
+        fill_to(fd, buf, pos + size + 2, deadline)?;
+        decoded.extend_from_slice(&buf[pos..pos + size]);
+        if &buf[pos + size..pos + size + 2] != b"\r\n" {
+            return Err(ChunkedBodyErr::Malformed);
+        }
+        pos += size + 2;
+    }
+}
+
+// ---------------------------------------------------------------------------
+// read_some — single epoll-park + read loop, bounded by a deadline.
+// ---------------------------------------------------------------------------
+//
+// Appends what it reads onto `buf`. Returns bytes read, 0 for EOF,
+// `ErrorKind::TimedOut` when `deadline` passes before the fd turns
+// readable, or the last io error.
+
+pub(crate) fn read_some(
+    fd: RawFd,
+    buf: &mut Vec<u8>,
+    chunk: usize,
+    deadline: Instant,
+) -> io::Result<usize> {
     // Loop to absorb EAGAIN: a readable wakeup followed by EAGAIN is
     // possible (signal race, etc). Re-park and retry rather than returning
-    // 0 (which would be confused with EOF by callers).
+    // 0 (which would be confused with EOF by callers). The deadline is an
+    // Instant, so spurious wakes don't reset the budget.
     loop {
-        smarm::wait_readable(fd)?;
+        let remaining = deadline.saturating_duration_since(Instant::now());
+        if remaining.is_zero() {
+            return Err(io::Error::new(ErrorKind::TimedOut, "read deadline elapsed"));
+        }
+        if !smarm::wait_readable_timeout(fd, remaining)? {
+            return Err(io::Error::new(ErrorKind::TimedOut, "read deadline elapsed"));
+        }
 
         let start = buf.len();
         buf.resize(start + chunk, 0);
@@ -262,13 +609,40 @@ fn read_some(fd: RawFd, buf: &mut Vec<u8>, chunk: usize) -> io::Result<usize> {
 }
 
 // ---------------------------------------------------------------------------
-// write_all — robust write loop.
+// try_write_once — single non-parking write attempt, result ignored.
 // ---------------------------------------------------------------------------
+//
+// For best-effort farewells (the 408) to clients we've decided to drop:
+// one non-blocking write syscall, no wait_writable park. A client that
+// stalls its read side must not be able to keep this actor alive past its
+// own timeout. The socket send buffer almost always has room for a
+// one-liner, so in practice the 408 lands.
 
-fn write_all(fd: RawFd, mut buf: &[u8]) -> io::Result<()> {
+fn try_write_once(fd: RawFd, buf: &[u8]) {
+    unsafe {
+        let _ = libc::write(fd, buf.as_ptr() as *const _, buf.len());
+    }
+}
+
+// ---------------------------------------------------------------------------
+// write_all — robust write loop, bounded by a deadline.
+// ---------------------------------------------------------------------------
+//
+// Mirrors read_some: each writability park is bounded by the remaining
+// budget. `ErrorKind::TimedOut` when the deadline passes before the bytes
+// are down — a client that stops reading must not pin this actor in
+// wait_writable forever (the write-side twin of slowloris).
+
+pub(crate) fn write_all(fd: RawFd, mut buf: &[u8], deadline: Instant) -> io::Result<()> {
     while !buf.is_empty() {
-        // Park on writability before each syscall.
-        smarm::wait_writable(fd)?;
+        // Park on writability before each syscall, bounded by the budget.
+        let remaining = deadline.saturating_duration_since(Instant::now());
+        if remaining.is_zero() {
+            return Err(io::Error::new(ErrorKind::TimedOut, "write deadline elapsed"));
+        }
+        if !smarm::wait_writable_timeout(fd, remaining)? {
+            return Err(io::Error::new(ErrorKind::TimedOut, "write deadline elapsed"));
+        }
 
         let n = unsafe {
             libc::write(fd, buf.as_ptr() as *const _, buf.len())
@@ -288,11 +662,89 @@ fn write_all(fd: RawFd, mut buf: &[u8]) -> io::Result<()> {
     Ok(())
 }
 
+// ---------------------------------------------------------------------------
+// pump_stream — drive a RespBody::Stream onto the wire.
+// ---------------------------------------------------------------------------
+//
+// The pull side of the v0.3 streaming design: the handler's producer actor
+// owns the Sender; this conn actor owns the socket and every write
+// deadline. We park in `recv()` between chunks — that park is stoppable
+// (a draining registry's `request_stop` unwinds us out of `park_current`
+// via the stop sentinel; fd + registry guards clean up), so an infinite
+// stream is force-stoppable at the drain deadline like any other in-flight
+// request. End of stream is the channel closing: every Sender dropped.
+//
+// Each chunk gets a FRESH write_timeout budget — a stream is expected to
+// outlive any whole-response clock; what is not tolerated is a single
+// write stalling. On write failure we return Err: the conn loop drops the
+// Receiver, and the producer's next `send` observes the closed channel and
+// should exit (that is the documented producer contract).
+//
+// `chunked` selects HTTP/1.1 chunked framing (hex-length CRLF payload
+// CRLF, terminated by a 0-chunk) vs HTTP/1.0 raw writes (EOF-delimited;
+// caller closes). Empty chunks are skipped — a zero-length chunk would
+// terminate the framing early.
+
+fn pump_stream(
+    fd: RawFd,
+    stream: StreamBody,
+    chunked: bool,
+    write_timeout: Duration,
+) -> io::Result<()> {
+    let write_chunk = |payload: &[u8]| -> io::Result<()> {
+        let deadline = Instant::now() + write_timeout;
+        if chunked {
+            let mut framed = Vec::with_capacity(payload.len() + 20);
+            framed.extend_from_slice(format!("{:x}\r\n", payload.len()).as_bytes());
+            framed.extend_from_slice(payload);
+            framed.extend_from_slice(b"\r\n");
+            write_all(fd, &framed, deadline)
+        } else {
+            write_all(fd, payload, deadline)
+        }
+    };
+
+    loop {
+        // With a heartbeat configured (SSE), the wait between chunks is the
+        // heartbeat interval; expiry emits the ping and keeps waiting. A
+        // ping write that stalls past write_timeout errors out below —
+        // that is the dead-client detector. Without one, plain recv():
+        // stoppable by the draining registry either way.
+        let msg = match &stream.heartbeat {
+            Some((interval, payload)) => match stream.rx.recv_timeout(*interval) {
+                Ok(chunk) => Some(chunk),
+                Err(smarm::RecvTimeoutError::Timeout) => {
+                    write_chunk(payload)?;
+                    continue;
+                }
+                Err(smarm::RecvTimeoutError::Disconnected) => None,
+            },
+            None => stream.rx.recv().ok(),
+        };
+
+        match msg {
+            Some(chunk) => {
+                if chunk.is_empty() {
+                    continue;
+                }
+                write_chunk(&chunk)?;
+            }
+            None => {
+                // All senders dropped: end of stream.
+                if chunked {
+                    write_all(fd, b"0\r\n\r\n", Instant::now() + write_timeout)?;
+                }
+                return Ok(());
+            }
+        }
+    }
+}
+
 // ---------------------------------------------------------------------------
 // Error responses for unparseable / malformed requests.
 // ---------------------------------------------------------------------------
 
-fn emit_error_response(fd: RawFd, err: &ParseError) {
+fn emit_error_response(fd: RawFd, err: &ParseError, deadline: Instant) {
     let resp: &[u8] = match err {
         ParseError::TooManyHeaders =>
             b"HTTP/1.1 431 Request Header Fields Too Large\r\ncontent-length: 0\r\nconnection: close\r\n\r\n",
@@ -305,5 +757,5 @@ fn emit_error_response(fd: RawFd, err: &ParseError) {
         _ =>
             b"HTTP/1.1 400 Bad Request\r\ncontent-length: 0\r\nconnection: close\r\n\r\n",
     };
-    let _ = write_all(fd, resp);
+    let _ = write_all(fd, resp, deadline);
 }

src/conn_registry.rs

@@ -0,0 +1,167 @@
+//! Connection registry — the shutdown coordinator (v0.2 chunk 2).
+//!
+//! A `gen_server` tracking live connection pids and their busy/idle
+//! state. Connection actors self-register as their first action and
+//! self-deregister via a drop guard (so panic unwinds deregister too);
+//! both casts come from the same sender, so Started always precedes
+//! Ended in the inbox. (The roadmap sketched the *listener* casting
+//! `{Started, pid}`, but then a short-lived conn's Ended could overtake
+//! its Started and leak a dead pid into the set forever. Self-
+//! registration makes the order a per-sender FIFO guarantee instead of
+//! a race.)
+//!
+//! Listeners are deliberately NOT tracked here: they shut down via a
+//! shared flag + timed accept-waits (see `serve`), never via
+//! `request_stop` — stopping pids that announce themselves is racy (the
+//! spawn-to-registration gap), and smarm's `request_stop` is lossy
+//! against an actor that is QUEUED and then parks without passing an
+//! observation point (see the v0.2 shutdown notes in the commit
+//! message). Connections don't suffer this in practice: every stop the
+//! registry issues targets a pid that just sent us a cast (so it is
+//! running or parked, both covered), and the force-stop path re-sweeps
+//! until the set empties.
+//!
+//! Drain protocol: `BeginDrain` stops every idle connection immediately
+//! and flips the registry into draining mode, in which any connection
+//! that *becomes* idle (finishes its in-flight request) is stopped on the
+//! spot. Busy connections are left to finish; `ForceStopConns` (sent by
+//! `serve` at the drain deadline) stops whatever remains. `request_stop`
+//! unwinds a conn actor parked in `wait_readable` safely (smarm's 06-10
+//! io fix) and `OwnedFd::drop` closes its socket on the way out.
+//!
+//! This server is also the planned introspection point for ws/channels
+//! (roadmap v0.4+), which is why it exists as its own module rather than
+//! being inlined into `serve`.
+
+use smarm::{GenServer, Pid, ServerBuilder, ServerRef};
+
+use std::collections::HashMap;
+
+// ---------------------------------------------------------------------------
+// Messages
+// ---------------------------------------------------------------------------
+
+pub enum Cast {
+    /// A connection actor started (self-registered, initially idle: it has
+    /// not parsed a request head yet).
+    ConnStarted(Pid),
+    /// Parsed a request head; a response is now owed.
+    ConnBusy(Pid),
+    /// Response written; parked (or about to park) waiting for the next
+    /// keep-alive request.
+    ConnIdle(Pid),
+    ConnEnded(Pid),
+    /// Stop idle conns now and stop each remaining conn as it goes idle.
+    BeginDrain,
+    /// Drain deadline passed: stop every remaining conn.
+    ForceStopConns,
+}
+
+pub enum Call {
+    ConnCount,
+}
+
+pub enum Reply {
+    ConnCount(usize),
+}
+
+// ---------------------------------------------------------------------------
+// Server
+// ---------------------------------------------------------------------------
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum ConnState {
+    Busy,
+    Idle,
+}
+
+#[derive(Default)]
+pub struct ConnRegistry {
+    conns:    HashMap<Pid, ConnState>,
+    draining: bool,
+}
+
+impl GenServer for ConnRegistry {
+    type Call  = Call;
+    type Reply = Reply;
+    type Cast  = Cast;
+    type Info  = ();
+
+    fn handle_call(&mut self, request: Call) -> Reply {
+        match request {
+            Call::ConnCount => Reply::ConnCount(self.conns.len()),
+        }
+    }
+
+    fn handle_cast(&mut self, request: Cast) {
+        match request {
+            Cast::ConnStarted(pid) => {
+                self.conns.insert(pid, ConnState::Idle);
+                if self.draining {
+                    // Listener-stop race: this conn was accepted just
+                    // before its listener died. Drain means no new work.
+                    smarm::request_stop(pid);
+                }
+            }
+            Cast::ConnBusy(pid) => {
+                if let Some(s) = self.conns.get_mut(&pid) {
+                    *s = ConnState::Busy;
+                }
+            }
+            Cast::ConnIdle(pid) => {
+                if let Some(s) = self.conns.get_mut(&pid) {
+                    *s = ConnState::Idle;
+                    if self.draining {
+                        // Finished its in-flight request; nothing more is
+                        // owed. The pid leaves the map via its drop
+                        // guard's ConnEnded once the unwind completes.
+                        smarm::request_stop(pid);
+                    }
+                }
+            }
+            Cast::ConnEnded(pid) => { self.conns.remove(&pid); }
+            Cast::BeginDrain => {
+                self.draining = true;
+                for (pid, state) in &self.conns {
+                    if *state == ConnState::Idle {
+                        smarm::request_stop(*pid);
+                    }
+                }
+            }
+            Cast::ForceStopConns => {
+                for pid in self.conns.keys() {
+                    smarm::request_stop(*pid);
+                }
+            }
+        }
+    }
+}
+
+pub fn start() -> ServerRef<ConnRegistry> {
+    ServerBuilder::new(ConnRegistry::default()).start()
+}
+
+// ---------------------------------------------------------------------------
+// Drop guard — self-deregistration on any exit path.
+// ---------------------------------------------------------------------------
+
+/// Casts `make(pid)` on drop. Runs on normal return, `request_stop`
+/// unwind, and panic unwind alike; the cast is infallible from the
+/// guard's perspective (a dead registry just returns an ignored Err).
+pub struct DeregisterGuard {
+    registry: ServerRef<ConnRegistry>,
+    pid:      Pid,
+    make:     fn(Pid) -> Cast,
+}
+
+impl DeregisterGuard {
+    pub fn new(registry: ServerRef<ConnRegistry>, pid: Pid, make: fn(Pid) -> Cast) -> Self {
+        Self { registry, pid, make }
+    }
+}
+
+impl Drop for DeregisterGuard {
+    fn drop(&mut self) {
+        let _ = self.registry.cast((self.make)(self.pid));
+    }
+}

src/lib.rs

@@ -24,10 +24,23 @@ pub mod router;
 pub mod parser;
 pub mod net;
 pub mod conn_actor;
+pub mod conn_registry;
 pub mod serve;
+pub mod sse;
+pub mod ws;
+pub mod pubsub;
+#[cfg(feature = "channels")]
+pub mod channels;
 
 // Re-exports — what most users want at the crate root.
-pub use conn::{Assigns, Body, Conn, HeaderMap, HttpVersion, Method, Params, RespBody};
+pub use conn::{Assigns, Body, Conn, HeaderMap, HttpVersion, Method, Params, RespBody, StreamBody};
 pub use plug::{Next, Pipeline, Plug};
 pub use router::Router;
-pub use serve::{serve, serve_with, Config};
+pub use sse::{EventSender, SseClosed};
+pub use pubsub::{PubSub, PubSubDown};
+#[cfg(feature = "channels")]
+pub use channels::{Channel, ChannelHub, ChannelSession, ChannelSocket, PrefixRouter, Status, TopicRouter};
+pub use ws::{Message, WsClosed, WsHandler, WsSender};
+pub use serve::{
+    serve, serve_with, serve_with_shutdown, shutdown_handle, Config, Handle, ShutdownSignal,
+};

src/net.rs

@@ -52,6 +52,13 @@ impl Drop for OwnedFd {
 // becomes the unique closer.
 unsafe impl Send for OwnedFd {}
 
+// SAFETY: shared references only expose `as_raw(&self)` — reading an
+// integer. No interior mutability; `into_raw` takes `self` by value and is
+// unreachable through a shared reference. Needed so a supervisor
+// `ChildSpec` factory (an `Fn` closure, hence shared across restarts) can
+// own its listener fd via `Arc<OwnedFd>`.
+unsafe impl Sync for OwnedFd {}
+
 // ---------------------------------------------------------------------------
 // bind_and_listen
 // ---------------------------------------------------------------------------

src/parser.rs

@@ -4,14 +4,13 @@
 //! copy, battle-tested). Body framing, keep-alive logic and response writing
 //! are ours.
 //!
-//! v1 body framing:
+//! Body framing:
 //!   - `Content-Length: N` — read exactly N bytes.
 //!   - No body header — empty body.
-//!   - `Transfer-Encoding: chunked` — deferred. Returns ParseError::Unsupported
-//!     and the connection actor responds 411 Length Required + close.
-//!
-//! Keep it stupid simple. Chunked decoding lands when something actually
-//! requests it.
+//!   - `Transfer-Encoding: chunked` (HTTP/1.1) — flagged in `ParsedHead`;
+//!     the connection actor decodes incrementally (`read_chunked_body`).
+//!     Chunked + Content-Length together, or chunked on HTTP/1.0, is
+//!     Malformed (request-smuggling ambiguity; RFC 7230 §3.3.3).
 
 use crate::conn::{Body, Conn, HeaderMap, HttpVersion, Method, RespBody};
 
@@ -30,8 +29,9 @@ pub enum ParseError {
     TooManyHeaders,
     /// `Content-Length` header could not be parsed as an integer.
     BadContentLength,
-    /// A wire feature we haven't implemented yet (e.g. chunked encoding).
-    /// Connection actor responds 411 + close.
+    /// A wire feature we haven't implemented. Currently unconstructed
+    /// (chunked decoding landed in v0.3); kept for future unsupported
+    /// framings. Connection actor responds 411 + close.
     Unsupported,
 }
 
@@ -50,6 +50,10 @@ pub struct ParsedHead {
     pub version:        HttpVersion,
     pub headers:        HeaderMap,
     pub content_length: Option<usize>,
+    /// `Transfer-Encoding: chunked` — the body is chunked-framed and the
+    /// connection actor decodes it (`read_chunked_body`). Mutually
+    /// exclusive with `content_length` (rejected as Malformed).
+    pub chunked:        bool,
     pub keep_alive:     bool,
     pub expect_100:     bool,
 }
@@ -130,7 +134,13 @@ pub fn parse_head(buf: &[u8], max_headers: usize) -> Result<ParsedHead, ParseErr
     }
 
     if chunked {
-        return Err(ParseError::Unsupported);
+        // Transfer-Encoding is an HTTP/1.1 mechanism; a 1.0 request
+        // carrying it is malformed. And a request carrying BOTH a
+        // Content-Length and TE: chunked is the classic request-smuggling
+        // ambiguity — RFC 7230 §3.3.3 lets a server reject it, and we do.
+        if version == HttpVersion::Http10 || content_length.is_some() {
+            return Err(ParseError::Malformed);
+        }
     }
 
     // Keep-alive logic, RFC 7230 §6.3:
@@ -149,6 +159,7 @@ pub fn parse_head(buf: &[u8], max_headers: usize) -> Result<ParsedHead, ParseErr
         version,
         headers,
         content_length,
+        chunked,
         keep_alive,
         expect_100,
     })
@@ -188,6 +199,7 @@ pub fn build_conn(head: ParsedHead, body: Body) -> Conn {
 pub fn serialise_response(conn: &Conn, keep_alive: bool) -> Vec<u8> {
     // Pre-size: status line ~30 + headers ~50/each + body. Good enough.
     let body_len  = conn.resp_body.len_hint();
+    let is_stream = matches!(conn.resp_body, RespBody::Stream(_));
     let mut out   = Vec::with_capacity(64 + conn.resp_headers.len() * 40 + body_len);
 
     let status = conn.status.unwrap_or(200);
@@ -202,11 +214,17 @@ pub fn serialise_response(conn: &Conn, keep_alive: bool) -> Vec<u8> {
     out.extend_from_slice(b"\r\n");
 
     // User headers — written first so subsequent injection can skip them.
+    // For Stream bodies WE own the framing: a user `content-length` or
+    // `transfer-encoding` is dropped rather than emitted (the combination
+    // of content-length + chunked is a smuggling vector, and a stream has
+    // no length to promise anyway).
     let mut wrote_content_length = false;
     let mut wrote_connection     = false;
 
     for (name, value) in conn.resp_headers.iter() {
         match name {
+            "content-length" if is_stream => continue,
+            "transfer-encoding" if is_stream => continue,
             "content-length" => wrote_content_length = true,
             "connection"     => wrote_connection     = true,
             _ => {}
@@ -217,22 +235,44 @@ pub fn serialise_response(conn: &Conn, keep_alive: bool) -> Vec<u8> {
         out.extend_from_slice(b"\r\n");
     }
 
-    if !wrote_content_length {
+    if is_stream {
+        // HTTP/1.1: chunked framing, connection reusable afterwards.
+        // HTTP/1.0: no chunked TE exists; the body is raw bytes delimited
+        // by EOF — the caller passes keep_alive = false and we emit
+        // `connection: close` below.
+        if conn.version == HttpVersion::Http11 {
+            out.extend_from_slice(b"transfer-encoding: chunked\r\n");
+        }
+    } else if !wrote_content_length && !(100..200).contains(&status) {
+        // 1xx responses have no body by definition (RFC 7230 §3.3.2) —
+        // injecting `content-length: 0` on the 101 upgrade response is a
+        // protocol violation some clients reject.
         out.extend_from_slice(b"content-length: ");
         out.extend_from_slice(body_len.to_string().as_bytes());
         out.extend_from_slice(b"\r\n");
     }
 
-    if !wrote_connection && !keep_alive {
+    if !wrote_connection {
+        if !keep_alive {
             out.extend_from_slice(b"connection: close\r\n");
+        } else if conn.version == HttpVersion::Http10 {
+            // HTTP/1.0 defaults to close: a connection we intend to keep
+            // open MUST be advertised back, or a spec-following client
+            // waits for an EOF that never comes (`ab -k` deadlocked on
+            // exactly this). 1.1 keep-alive is the default and stays
+            // implicit.
+            out.extend_from_slice(b"connection: keep-alive\r\n");
+        }
     }
 
     out.extend_from_slice(b"\r\n");
 
-    // Body.
+    // Fixed bodies are written inline with the head; a Stream body is
+    // pumped by the connection actor after this head goes on the wire.
     match &conn.resp_body {
         RespBody::Empty     => {}
         RespBody::Bytes(b)  => out.extend_from_slice(b),
+        RespBody::Stream(_) => {}
     }
 
     out
@@ -340,11 +380,28 @@ mod tests {
     }
 
     #[test]
-    fn parse_chunked_unsupported() {
+    fn parse_chunked_is_flagged() {
         let req = b"POST /a HTTP/1.1\r\nHost: x\r\nTransfer-Encoding: chunked\r\n\r\n";
+        let head = parse_head(req, 64).unwrap();
+        assert!(head.chunked);
+        assert_eq!(head.content_length, None);
+    }
+
+    #[test]
+    fn parse_chunked_plus_content_length_is_malformed() {
+        let req = b"POST /a HTTP/1.1\r\nHost: x\r\nContent-Length: 5\r\nTransfer-Encoding: chunked\r\n\r\n";
         match parse_head(req, 64) {
-            Err(ParseError::Unsupported) => {}
-            _ => panic!("expected Unsupported for chunked"),
+            Err(ParseError::Malformed) => {}
+            _ => panic!("expected Malformed for CL + chunked"),
+        }
+    }
+
+    #[test]
+    fn parse_chunked_on_http10_is_malformed() {
+        let req = b"POST /a HTTP/1.0\r\nHost: x\r\nTransfer-Encoding: chunked\r\n\r\n";
+        match parse_head(req, 64) {
+            Err(ParseError::Malformed) => {}
+            _ => panic!("expected Malformed for chunked on 1.0"),
         }
     }
 
@@ -366,6 +423,61 @@ mod tests {
         assert!(s.contains("connection: close"));
     }
 
+    #[test]
+    fn serialise_stream_http11_is_chunked_no_content_length() {
+        let (_tx, rx) = smarm::channel::<Vec<u8>>();
+        let conn = Conn::new().put_status(200).put_body(RespBody::from(rx));
+        let bytes = serialise_response(&conn, true);
+        let s = std::str::from_utf8(&bytes).unwrap();
+        assert!(s.contains("transfer-encoding: chunked"));
+        assert!(!s.contains("content-length"));
+        assert!(s.ends_with("\r\n\r\n")); // head only, no body bytes
+    }
+
+    #[test]
+    fn serialise_stream_strips_user_framing_headers() {
+        let (_tx, rx) = smarm::channel::<Vec<u8>>();
+        let conn = Conn::new().put_status(200)
+            .put_header("content-length", "999")
+            .put_header("transfer-encoding", "gzip")
+            .put_body(RespBody::from(rx));
+        let bytes = serialise_response(&conn, true);
+        let s = std::str::from_utf8(&bytes).unwrap();
+        assert!(!s.contains("content-length"));
+        assert!(!s.contains("gzip"));
+        assert!(s.contains("transfer-encoding: chunked"));
+    }
+
+    #[test]
+    fn serialise_stream_http10_no_te_and_closes() {
+        let (_tx, rx) = smarm::channel::<Vec<u8>>();
+        let mut conn = Conn::new().put_status(200).put_body(RespBody::from(rx));
+        conn.version = HttpVersion::Http10;
+        // The conn actor forces keep_alive=false for a 1.0 stream.
+        let bytes = serialise_response(&conn, false);
+        let s = std::str::from_utf8(&bytes).unwrap();
+        assert!(!s.contains("transfer-encoding"));
+        assert!(!s.contains("content-length"));
+        assert!(s.contains("connection: close"));
+    }
+
+    #[test]
+    fn serialise_http10_keepalive_is_echoed() {
+        let mut conn = Conn::new().put_status(200).put_body("hi");
+        conn.version = HttpVersion::Http10;
+        let bytes = serialise_response(&conn, true);
+        let s = std::str::from_utf8(&bytes).unwrap();
+        assert!(s.contains("connection: keep-alive"), "head: {s}");
+    }
+
+    #[test]
+    fn serialise_http11_keepalive_stays_implicit() {
+        let conn = Conn::new().put_status(200).put_body("hi");
+        let bytes = serialise_response(&conn, true);
+        let s = std::str::from_utf8(&bytes).unwrap();
+        assert!(!s.contains("connection:"), "head: {s}");
+    }
+
     #[test]
     fn serialise_user_content_length_is_respected() {
         let conn = Conn::new().put_status(200)

src/pubsub.rs

@@ -0,0 +1,512 @@
+//! `urus::pubsub` — local-node topic pub/sub, phoenix_pubsub-shaped.
+//!
+//! Deliberately independent of HTTP: nothing here imports the rest of
+//! urus, only smarm. Usable from any smarm app; candidate for crate
+//! extraction later.
+//!
+//! # Shape (v0.5 design, user-ratified)
+//!
+//! - **Generic per instance** (`PubSub<M>`): zero-cost dispatch, no
+//!   downcasts. One instance per message domain; heterogeneous events on
+//!   one bus are an app-side `enum M`.
+//! - **Subscribe returns a `Receiver<Arc<M>>`**: the subscriber owns its
+//!   receive loop and composes with the v0.4 ws outbound pattern (a relay
+//!   actor pumping the receiver into a `WsSender` clone). One fresh
+//!   receiver per subscription; fan-in (`subscribe_with(topic, sender)`)
+//!   is a compatible later addition if wanted.
+//! - **Unbounded mailboxes**: `broadcast` never blocks the topic table —
+//!   a bounded-block policy would head-of-line-block *every* topic behind
+//!   one slow subscriber, and bounded-drop silently loses messages.
+//!   Memory risk is a live-but-not-receiving subscriber, bounded by two
+//!   cleanup paths: monitor `Down` on subscriber death, and pruning on
+//!   send failure when a receiver was dropped. Bench before sharding.
+//! - **User-owned handle**: construct a `PubSub<M>`, clone it around
+//!   (handler closures already thread state this way). No global named
+//!   instance — see the module note on `register` below.
+//! - **One subscription per `(pid, topic)`**: subscribe is idempotent;
+//!   re-subscribing replaces the sender (the old receiver's channel
+//!   closes). Kills the silent double-delivery bug class.
+//!
+//! # Cleanup mechanics
+//!
+//! The table monitors each subscriber pid **once** (first subscribe) via
+//! the gen_server [`Watcher`]; the `Down` removes the pid from every
+//! topic — a full table scan, deliberately: deaths are rare and topic
+//! counts small at this stage, a pid→topics reverse index is the
+//! documented optimisation if that ever measures hot (same spirit as the
+//! roadmap's "don't pre-shard"). A pid that unsubscribes from everything
+//! but stays alive keeps its (one-shot, inert) monitor until death;
+//! that's a bounded bookkeeping entry, not a leak.
+//!
+//! # Construction must happen in-runtime
+//!
+//! [`PubSub::new`] spawns the table actor, which smarm only permits from
+//! inside `Runtime::run`. Pipelines are built *before* `serve*` boots the
+//! runtime, so the working pattern (same constraint crud's store hits) is
+//! lazy init from the first handler — but with a **non-static**
+//! `Arc<OnceLock<PubSub<M>>>` captured by the route closure, NOT a
+//! `static`: when the drained pipeline drops at graceful shutdown, the
+//! cell (and thus the last handle) drops in-runtime, the table's inbox
+//! closes, and the table exits — `serve_with_shutdown` returns. A
+//! `static` pins the table forever and blocks smarm's all-done. The same
+//! reasoning forbids long-lived consumer actors (relays, producers) from
+//! holding a `PubSub` clone: relay holds table's inbox open, table holds
+//! relay's receiver open, neither exits. Relays take the `Receiver` only.
+//! See `examples/ws_chat.rs` and the `shutdown_with_open_chat_terminates`
+//! integration test for the full chain.
+//!
+//! # Why there is no `register(name)` helper (yet)
+//!
+//! smarm's registry maps `name → Pid`, but a `Pid` cannot be turned back
+//! into a `ServerRef` (the ref *is* the inbox sender). A useful named
+//! lookup therefore needs either smarm support (registry-held senders)
+//! or a process-global type-erased map here — both against the grain of
+//! the ratified design. Deferred; pass the handle.
+
+use std::collections::{HashMap, HashSet};
+use std::fmt;
+use std::sync::Arc;
+
+use smarm::gen_server::{self, GenServer, ServerCtx};
+use smarm::{channel, Down, Pid, Receiver, Sender, ServerRef, Watcher};
+
+// ---------------------------------------------------------------------------
+// Public handle
+// ---------------------------------------------------------------------------
+
+/// The topic table is gone — its gen_server actor exited (panic or runtime
+/// shutdown). Every operation on the handle fails with this from then on.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct PubSubDown;
+
+impl fmt::Display for PubSubDown {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "pubsub topic table is down")
+    }
+}
+
+impl std::error::Error for PubSubDown {}
+
+/// A clonable handle to one pub/sub instance (one topic table actor).
+///
+/// Payloads are broadcast as `Arc<M>`: one allocation per broadcast, not
+/// per subscriber.
+pub struct PubSub<M: Send + Sync + 'static> {
+    server: ServerRef<Table<M>>,
+}
+
+impl<M: Send + Sync + 'static> Clone for PubSub<M> {
+    fn clone(&self) -> Self {
+        PubSub { server: self.server.clone() }
+    }
+}
+
+impl<M: Send + Sync + 'static> Default for PubSub<M> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<M: Send + Sync + 'static> PubSub<M> {
+    /// Start a fresh topic table. Must run inside the smarm runtime (it
+    /// spawns the table's gen_server actor). The table lives until the
+    /// last handle is dropped.
+    pub fn new() -> Self {
+        PubSub { server: gen_server::start(Table::new()) }
+    }
+
+    /// Subscribe the **calling actor** to `topic`. Returns the receiving
+    /// end; messages arrive as `Arc<M>`. Idempotent per `(pid, topic)`:
+    /// subscribing again replaces the sender, closing the previously
+    /// returned receiver.
+    ///
+    /// The subscription is cleaned up when the calling actor dies. If the
+    /// receive loop runs in a *different* actor than the session that
+    /// should scope the subscription, use [`subscribe_as`](Self::subscribe_as)
+    /// to pin cleanup to the right pid (e.g. a ws connection actor
+    /// subscribing, with a spawned relay doing the receiving).
+    pub fn subscribe(&self, topic: impl Into<String>) -> Result<Receiver<Arc<M>>, PubSubDown> {
+        self.subscribe_as(smarm::self_pid(), topic)
+    }
+
+    /// [`subscribe`](Self::subscribe), but the subscription's lifetime is
+    /// tied to `pid` instead of the calling actor.
+    pub fn subscribe_as(
+        &self,
+        pid: Pid,
+        topic: impl Into<String>,
+    ) -> Result<Receiver<Arc<M>>, PubSubDown> {
+        let (tx, rx) = channel();
+        // A call, not a cast: when this returns the table is updated, so
+        // a broadcast issued right after by the same caller is seen.
+        match self.server.call(Call::Subscribe { topic: topic.into(), pid, tx }) {
+            Ok(_) => Ok(rx),
+            Err(_) => Err(PubSubDown),
+        }
+    }
+
+    /// Drop the calling actor's subscription to `topic` (its receiver's
+    /// channel closes). No-op if not subscribed.
+    pub fn unsubscribe(&self, topic: impl Into<String>) -> Result<(), PubSubDown> {
+        self.unsubscribe_as(smarm::self_pid(), topic)
+    }
+
+    /// [`unsubscribe`](Self::unsubscribe) for an explicit pid.
+    pub fn unsubscribe_as(&self, pid: Pid, topic: impl Into<String>) -> Result<(), PubSubDown> {
+        self.server
+            .cast(Cast::Unsubscribe { topic: topic.into(), pid })
+            .map_err(|_| PubSubDown)
+    }
+
+    /// Broadcast `msg` to every subscriber of `topic`. Never blocks on
+    /// subscribers (unbounded mailboxes); returns once the table has the
+    /// request queued.
+    pub fn broadcast(&self, topic: impl Into<String>, msg: M) -> Result<(), PubSubDown> {
+        self.cast_broadcast(topic.into(), msg, None)
+    }
+
+    /// [`broadcast`](Self::broadcast), skipping delivery to `from` —
+    /// pass `smarm::self_pid()` for the phoenix `broadcast_from` shape
+    /// ("everyone in the room but me").
+    pub fn broadcast_from(
+        &self,
+        from: Pid,
+        topic: impl Into<String>,
+        msg: M,
+    ) -> Result<(), PubSubDown> {
+        self.cast_broadcast(topic.into(), msg, Some(from))
+    }
+
+    /// Number of live subscriptions on `topic`. Counts entries in the
+    /// table — a subscriber whose receiver was dropped but hasn't been
+    /// pruned yet (no broadcast since, still alive) is still counted.
+    pub fn subscriber_count(&self, topic: impl Into<String>) -> Result<usize, PubSubDown> {
+        match self.server.call(Call::Count { topic: topic.into() }) {
+            Ok(Reply::Count(n)) => Ok(n),
+            Ok(Reply::Subscribed) => unreachable!("Count call answered with Subscribed"),
+            Err(_) => Err(PubSubDown),
+        }
+    }
+
+    /// The topic table actor's pid — for introspection / registry use.
+    pub fn pid(&self) -> Pid {
+        self.server.pid()
+    }
+
+    fn cast_broadcast(&self, topic: String, msg: M, skip: Option<Pid>) -> Result<(), PubSubDown> {
+        self.server
+            .cast(Cast::Broadcast { topic, msg: Arc::new(msg), skip })
+            .map_err(|_| PubSubDown)
+    }
+}
+
+// ---------------------------------------------------------------------------
+// The table gen_server
+// ---------------------------------------------------------------------------
+
+enum Call<M> {
+    Subscribe { topic: String, pid: Pid, tx: Sender<Arc<M>> },
+    Count { topic: String },
+}
+
+enum Reply {
+    Subscribed,
+    Count(usize),
+}
+
+enum Cast<M> {
+    Unsubscribe { topic: String, pid: Pid },
+    Broadcast { topic: String, msg: Arc<M>, skip: Option<Pid> },
+}
+
+struct Table<M: Send + Sync + 'static> {
+    topics: HashMap<String, HashMap<Pid, Sender<Arc<M>>>>,
+    /// Pids we already hold a monitor for. Monitors are one-shot and
+    /// created at most once per live pid (first subscribe); `handle_down`
+    /// retires the entry so a reused-slot pid (fresh generation) gets a
+    /// fresh monitor.
+    monitored: HashSet<Pid>,
+    watcher: Option<Watcher>,
+}
+
+impl<M: Send + Sync + 'static> Table<M> {
+    fn new() -> Self {
+        Table { topics: HashMap::new(), monitored: HashSet::new(), watcher: None }
+    }
+}
+
+impl<M: Send + Sync + 'static> GenServer for Table<M> {
+    type Call = Call<M>;
+    type Reply = Reply;
+    type Cast = Cast<M>;
+    type Info = ();
+
+    fn init(&mut self, ctx: &ServerCtx) {
+        self.watcher = Some(ctx.watcher());
+    }
+
+    fn handle_call(&mut self, request: Call<M>) -> Reply {
+        match request {
+            Call::Subscribe { topic, pid, tx } => {
+                if self.monitored.insert(pid) {
+                    let m = smarm::monitor(pid);
+                    self.watcher
+                        .as_ref()
+                        .expect("watcher set in init")
+                        .watch(m);
+                }
+                // Insert replaces: idempotent per (pid, topic); the old
+                // sender drops and the stale receiver's channel closes.
+                self.topics.entry(topic).or_default().insert(pid, tx);
+                Reply::Subscribed
+            }
+            Call::Count { topic } => {
+                Reply::Count(self.topics.get(&topic).map_or(0, HashMap::len))
+            }
+        }
+    }
+
+    fn handle_cast(&mut self, request: Cast<M>) {
+        match request {
+            Cast::Unsubscribe { topic, pid } => {
+                if let Some(subs) = self.topics.get_mut(&topic) {
+                    subs.remove(&pid);
+                    if subs.is_empty() {
+                        self.topics.remove(&topic);
+                    }
+                }
+            }
+            Cast::Broadcast { topic, msg, skip } => {
+                let Some(subs) = self.topics.get_mut(&topic) else { return };
+                // Prune-on-send-failure: a dropped receiver (subscriber
+                // alive but done listening, e.g. ws conn reaped at
+                // write_timeout) is removed lazily here; subscriber
+                // *death* is handled eagerly by the monitor.
+                subs.retain(|pid, tx| {
+                    if skip == Some(*pid) {
+                        return true;
+                    }
+                    tx.send(Arc::clone(&msg)).is_ok()
+                });
+                if subs.is_empty() {
+                    self.topics.remove(&topic);
+                }
+            }
+        }
+    }
+
+    fn handle_down(&mut self, down: Down) {
+        self.monitored.remove(&down.pid);
+        // Full scan, by design — see the module docs.
+        self.topics.retain(|_, subs| {
+            subs.remove(&down.pid);
+            !subs.is_empty()
+        });
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Tests (runtime-backed: results collected outside, asserted after run)
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::sync::Mutex;
+    use std::time::Duration;
+
+    /// Poll `f` until it returns true or ~2s elapse. For the
+    /// asynchronous cleanup paths (monitor Down delivery).
+    fn eventually(mut f: impl FnMut() -> bool) -> bool {
+        for _ in 0..200 {
+            if f() {
+                return true;
+            }
+            smarm::sleep(Duration::from_millis(10));
+        }
+        false
+    }
+
+    #[test]
+    fn broadcast_reaches_all_subscribers_once() {
+        let got = Arc::new(Mutex::new(Vec::<(u32, String)>::new()));
+        let got2 = got.clone();
+        smarm::run(move || {
+            let ps = PubSub::<String>::new();
+            let mut handles = Vec::new();
+            for i in 0..2u32 {
+                let ps = ps.clone();
+                let got = got2.clone();
+                handles.push(smarm::spawn(move || {
+                    let rx = ps.subscribe("room:a").unwrap();
+                    let msg = rx.recv().unwrap();
+                    got.lock().unwrap().push((i, (*msg).clone()));
+                }));
+            }
+            // Subscribes are calls from the spawned actors; wait until
+            // both are in the table before broadcasting.
+            assert!(eventually(|| ps.subscriber_count("room:a").unwrap() == 2));
+            ps.broadcast("room:a", "hello".to_string()).unwrap();
+            for h in handles {
+                h.join().unwrap();
+            }
+        });
+        let mut v = got.lock().unwrap().clone();
+        v.sort();
+        assert_eq!(v, vec![(0, "hello".into()), (1, "hello".into())]);
+    }
+
+    #[test]
+    fn arc_payload_is_shared_not_cloned() {
+        let ptrs = Arc::new(Mutex::new(Vec::<usize>::new()));
+        let ptrs2 = ptrs.clone();
+        smarm::run(move || {
+            let ps = PubSub::<Vec<u8>>::new();
+            let mut handles = Vec::new();
+            for _ in 0..2 {
+                let ps = ps.clone();
+                let ptrs = ptrs2.clone();
+                handles.push(smarm::spawn(move || {
+                    let rx = ps.subscribe("t").unwrap();
+                    let msg = rx.recv().unwrap();
+                    ptrs.lock().unwrap().push(Arc::as_ptr(&msg) as usize);
+                }));
+            }
+            assert!(eventually(|| ps.subscriber_count("t").unwrap() == 2));
+            ps.broadcast("t", vec![1, 2, 3]).unwrap();
+            for h in handles {
+                h.join().unwrap();
+            }
+        });
+        let v = ptrs.lock().unwrap();
+        assert_eq!(v.len(), 2);
+        assert_eq!(v[0], v[1], "both subscribers should see the same allocation");
+    }
+
+    #[test]
+    fn broadcast_from_skips_the_sender() {
+        let got = Arc::new(Mutex::new(Vec::<String>::new()));
+        let got2 = got.clone();
+        smarm::run(move || {
+            let ps = PubSub::<String>::new();
+            let ps_loud = ps.clone();
+            let got = got2.clone();
+            let loud = smarm::spawn(move || {
+                let rx = ps_loud.subscribe("room").unwrap();
+                ps_loud
+                    .broadcast_from(smarm::self_pid(), "room", "from loud".into())
+                    .unwrap();
+                // Must receive the OTHER broadcast only.
+                let msg = rx.recv().unwrap();
+                got.lock().unwrap().push(format!("loud got {}", *msg));
+            });
+            let rx = ps.subscribe("room").unwrap();
+            assert!(eventually(|| ps.subscriber_count("room").unwrap() == 2));
+            ps.broadcast("room", "for everyone".into()).unwrap();
+            let first = rx.recv().unwrap();
+            let second = rx.recv().unwrap();
+            got2.lock()
+                .unwrap()
+                .push(format!("root got {} then {}", *first, *second));
+            loud.join().unwrap();
+        });
+        let v = got.lock().unwrap();
+        assert!(v.contains(&"loud got for everyone".to_string()), "{v:?}");
+        // Root (not the broadcast_from sender) receives both, in order.
+        assert!(
+            v.contains(&"root got from loud then for everyone".to_string())
+                || v.contains(&"root got for everyone then from loud".to_string()),
+            "{v:?}"
+        );
+    }
+
+    #[test]
+    fn unsubscribe_closes_the_receiver_and_stops_delivery() {
+        let ok = Arc::new(Mutex::new(false));
+        let ok2 = ok.clone();
+        smarm::run(move || {
+            let ps = PubSub::<u32>::new();
+            let rx = ps.subscribe("t").unwrap();
+            ps.unsubscribe("t").unwrap();
+            // Unsubscribe is a cast; the table holds the only sender, so
+            // once processed the channel closes and recv errs.
+            assert!(eventually(|| ps.subscriber_count("t").unwrap() == 0));
+            assert!(rx.recv().is_err());
+            ps.broadcast("t", 7).unwrap(); // no subscribers: no-op, no panic
+            *ok2.lock().unwrap() = true;
+        });
+        assert!(*ok.lock().unwrap());
+    }
+
+    #[test]
+    fn resubscribe_replaces_the_old_subscription() {
+        let got = Arc::new(Mutex::new((0u32, false)));
+        let got2 = got.clone();
+        smarm::run(move || {
+            let ps = PubSub::<u32>::new();
+            let rx_old = ps.subscribe("t").unwrap();
+            let rx_new = ps.subscribe("t").unwrap();
+            assert_eq!(ps.subscriber_count("t").unwrap(), 1, "idempotent per (pid, topic)");
+            ps.broadcast("t", 42).unwrap();
+            let v = *rx_new.recv().unwrap();
+            let old_closed = rx_old.recv().is_err();
+            *got2.lock().unwrap() = (v, old_closed);
+        });
+        assert_eq!(*got.lock().unwrap(), (42, true));
+    }
+
+    #[test]
+    fn dead_subscriber_is_pruned_by_the_monitor() {
+        let ok = Arc::new(Mutex::new(false));
+        let ok2 = ok.clone();
+        smarm::run(move || {
+            let ps = PubSub::<u32>::new();
+            let ps2 = ps.clone();
+            let h = smarm::spawn(move || {
+                let _rx = ps2.subscribe("t").unwrap();
+                // Exit without ever receiving: rx drops with the stack.
+            });
+            h.join().unwrap();
+            // No broadcast issued — this MUST be the monitor path, not
+            // prune-on-send-failure.
+            *ok2.lock().unwrap() = eventually(|| ps.subscriber_count("t").unwrap() == 0);
+        });
+        assert!(*ok.lock().unwrap(), "monitor Down never pruned the dead subscriber");
+    }
+
+    #[test]
+    fn dropped_receiver_is_pruned_on_next_broadcast() {
+        let counts = Arc::new(Mutex::new((0usize, 0usize)));
+        let counts2 = counts.clone();
+        smarm::run(move || {
+            let ps = PubSub::<u32>::new();
+            let rx = ps.subscribe("t").unwrap();
+            drop(rx);
+            let before = ps.subscriber_count("t").unwrap();
+            ps.broadcast("t", 1).unwrap();
+            let mut after = ps.subscriber_count("t").unwrap();
+            // Casts are ordered but count is a call that can overtake
+            // nothing here — same inbox, so after the broadcast cast is
+            // handled. Still poll defensively.
+            if after != 0 {
+                after = if eventually(|| ps.subscriber_count("t").unwrap() == 0) { 0 } else { after };
+            }
+            *counts2.lock().unwrap() = (before, after);
+        });
+        assert_eq!(*counts.lock().unwrap(), (1, 0));
+    }
+
+    #[test]
+    fn topics_are_independent() {
+        let got = Arc::new(Mutex::new(Vec::<u32>::new()));
+        let got2 = got.clone();
+        smarm::run(move || {
+            let ps = PubSub::<u32>::new();
+            let rx_a = ps.subscribe("a").unwrap();
+            ps.broadcast("b", 99).unwrap(); // nobody on b; must not reach a
+            ps.broadcast("a", 1).unwrap();
+            got2.lock().unwrap().push(*rx_a.recv().unwrap());
+        });
+        assert_eq!(*got.lock().unwrap(), vec![1]);
+    }
+}

src/serve.rs

@@ -13,12 +13,17 @@
 //! waiting on "the same fd").
 
 use crate::conn_actor::{run_connection, ConnLimits};
+use crate::conn_registry::{self, Call, Cast, ConnRegistry, Reply};
 use crate::net::{accept_nonblocking, bind_and_listen, OwnedFd};
 use crate::plug::Pipeline;
 
+use smarm::{ChildSpec, OneForOne, Restart, ServerRef, Strategy};
+
 use std::io::{self, ErrorKind};
 use std::net::{SocketAddr, ToSocketAddrs};
 use std::os::fd::RawFd;
+use std::sync::atomic::{AtomicBool, AtomicU32, Ordering};
+use std::sync::Arc;
 use std::time::Duration;
 
 // ---------------------------------------------------------------------------
@@ -33,7 +38,21 @@ pub struct Config {
     pub max_header_count:   usize,
     pub read_buf_size:      usize,
     pub request_timeout:    Duration,
+    /// Per-write budget for response bytes (the fixed head+body write, and
+    /// each streamed chunk). See `ConnLimits::write_timeout`.
+    pub write_timeout:      Duration,
     pub max_body_bytes:     usize,
+    /// How long a graceful shutdown waits for in-flight requests before
+    /// force-stopping the remaining connections. Idle keep-alive
+    /// connections are closed immediately on shutdown and do not run the
+    /// clock out.
+    pub drain_timeout:      Duration,
+    /// WebSocket: cap on a single frame's payload (header-checked
+    /// before buffering; violation closes 1009).
+    pub max_frame_payload:  usize,
+    /// WebSocket: cap on a complete reassembled message (spans
+    /// fragments; violation closes 1009).
+    pub max_message_bytes:  usize,
     /// Number of smarm scheduler OS threads. `None` means smarm's default
     /// (one per CPU). Set this to a small fixed number in tests so multiple
     /// concurrent test servers don't oversubscribe the host.
@@ -53,7 +72,11 @@ impl Config {
             max_header_count:   64,
             read_buf_size:      8 * 1024,
             request_timeout:    Duration::from_secs(30),
+            write_timeout:      Duration::from_secs(30),
             max_body_bytes:     16 * 1024 * 1024,
+            drain_timeout:      Duration::from_secs(30),
+            max_frame_payload:  1024 * 1024,
+            max_message_bytes:  4 * 1024 * 1024,
             scheduler_threads:  None,
         }
     }
@@ -65,6 +88,10 @@ impl Config {
             max_head_bytes:     64 * 1024,
             max_body_bytes:     self.max_body_bytes,
             keep_alive_timeout: self.keep_alive_timeout,
+            request_timeout:    self.request_timeout,
+            write_timeout:      self.write_timeout,
+            max_frame_payload:  self.max_frame_payload,
+            max_message_bytes:  self.max_message_bytes,
         }
     }
 }
@@ -85,9 +112,43 @@ fn dup_fd(fd: RawFd) -> io::Result<OwnedFd> {
 // listener actor body
 // ---------------------------------------------------------------------------
 
-fn listener_loop(listener: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
+/// Test-only fault injection. When nonzero, the next accept-loop iteration
+/// of whichever listener gets there first decrements this and panics —
+/// *before* calling `accept`, so a pending connection stays in the kernel
+/// backlog and must be picked up by the restarted listener. Cost when idle
+/// is one relaxed load per accept-loop iteration (each of which already
+/// pays a syscall). Not public API.
+#[doc(hidden)]
+pub static INJECT_LISTENER_PANICS: AtomicU32 = AtomicU32::new(0);
+
+fn listener_loop(
+    listener: Arc<OwnedFd>,
+    pipeline: Pipeline,
+    limits: ConnLimits,
+    registry: ServerRef<ConnRegistry>,
+    shutdown: Arc<AtomicBool>,
+) {
     let fd = listener.as_raw();
+
     loop {
+        // Self-termination on shutdown — the ONLY way a listener exits at
+        // shutdown, and deliberately a normal return: under
+        // `Restart::Transient` a normal exit is terminal, so the
+        // supervisor's active-count drains and `sup.run()` returns on its
+        // own. No pid is ever `request_stop`ped, which sidesteps both the
+        // spawn-to-registration race of self-announced pids and smarm's
+        // lossy stop-while-QUEUED window (a flag is wake-free and
+        // race-free; a freshly spawned listener observes it on its very
+        // first iteration, a parked one within LISTENER_TICK).
+        if shutdown.load(Ordering::Relaxed) {
+            return;
+        }
+        if INJECT_LISTENER_PANICS
+            .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |n| n.checked_sub(1))
+            .is_ok()
+        {
+            panic!("urus: injected listener panic (test hook)");
+        }
         match accept_nonblocking(fd) {
             Ok(client) => {
                 // Hand the fd off to a new connection actor. spawn() is
@@ -95,15 +156,27 @@ fn listener_loop(listener: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
                 // shared lock.
                 let p = pipeline.clone();
                 let l = limits;
-                smarm::spawn(move || run_connection(client, p, l));
+                let r = registry.clone();
+                smarm::spawn(move || run_connection(client, p, l, r));
             }
             Err(e) if e.kind() == ErrorKind::WouldBlock => {
                 // No pending connection. Park until the listener is
-                // readable again, then retry.
-                if let Err(we) = smarm::wait_readable(fd) {
-                    // epoll registration failed — fatal for this listener.
-                    eprintln!("urus: listener wait_readable failed: {we}");
-                    return;
+                // readable or the tick elapses; either way we come back
+                // around through the shutdown-flag check above.
+                match smarm::wait_readable_timeout(fd, LISTENER_TICK) {
+                    Ok(_ready) => {} // ready or tick — loop re-checks, retries accept
+                    Err(we) => {
+                        // epoll registration failed. Under Transient
+                        // supervision a normal return is terminal but a
+                        // panic restarts us — and a failed wait IS
+                        // abnormal, so panic: a transient failure (e.g.
+                        // EMFILE on the epoll set) heals by restart
+                        // instead of silently shrinking the pool. (smarm
+                        // catches actor panics in the trampoline; this is
+                        // a Signal::Panic to the supervisor, not process
+                        // noise.)
+                        panic!("urus: listener wait_readable failed: {we}");
+                    }
                 }
             }
             Err(e) if e.kind() == ErrorKind::Interrupted => {
@@ -119,62 +192,232 @@ fn listener_loop(listener: OwnedFd, pipeline: Pipeline, limits: ConnLimits) {
             }
         }
     }
-    // listener OwnedFd drops here, closing the dup'd fd.
+    // The Arc clone we were started with drops here (normal exit or
+    // unwind), but the ChildSpec factory holds another — the fd outlives
+    // any one incarnation of this listener.
 }
 
 // ---------------------------------------------------------------------------
-// serve_with — main entry. Boots smarm, spawns listeners, blocks.
+// Handle / ShutdownSignal — graceful shutdown plumbing.
+// ---------------------------------------------------------------------------
+
+/// How often the root actor polls for a shutdown signal (see
+/// `serve_with_shutdown` for why this is a poll); bounds shutdown latency.
+const SHUTDOWN_POLL: Duration = Duration::from_millis(100);
+
+/// Listener accept-waits are timed at this tick; the shutdown flag is
+/// observed at the top of every accept-loop iteration, so this bounds how
+/// long a fully idle listener takes to notice shutdown. It is the SOLE
+/// listener-shutdown mechanism (no `request_stop` — see the shutdown
+/// sequence notes). Idle cost: one timer wake per listener per tick.
+const LISTENER_TICK: Duration = Duration::from_millis(250);
+
+/// A clonable trigger for graceful shutdown. Safe to use from any OS
+/// thread (the send only enqueues; the serving side polls), e.g. from a
+/// signal-handling thread.
+#[derive(Clone)]
+pub struct Handle {
+    tx: smarm::Sender<()>,
+}
+
+impl Handle {
+    /// Begin graceful shutdown: stop accepting, close idle keep-alive
+    /// connections, drain in-flight requests up to `Config.drain_timeout`,
+    /// then force-stop stragglers. `serve_with_shutdown` returns once the
+    /// runtime has wound down. Idempotent; extra calls are no-ops.
+    pub fn shutdown(&self) {
+        let _ = self.tx.send(());
+    }
+}
+
+/// The receiving half consumed by [`serve_with_shutdown`].
+pub struct ShutdownSignal {
+    rx: smarm::Receiver<()>,
+}
+
+/// Create a connected [`Handle`]/[`ShutdownSignal`] pair.
+pub fn shutdown_handle() -> (Handle, ShutdownSignal) {
+    let (tx, rx) = smarm::channel();
+    (Handle { tx }, ShutdownSignal { rx })
+}
+
+// ---------------------------------------------------------------------------
+// serve_with_shutdown — main entry. Boots smarm, supervises listeners,
+// blocks until shutdown.
 // ---------------------------------------------------------------------------
 //
 // Boots an smarm runtime (one OS thread per CPU by default — see smarm's
-// `Config::default()`) and runs until externally killed. We don't wire a
-// graceful-shutdown signal in v1; the runtime exits when all actors exit,
-// which they don't (listener loops are infinite). Ctrl-C is your friend.
+// `Config::default()`). The root actor starts the connection registry and
+// a one-for-one supervisor over the listener pool, then blocks on the
+// shutdown signal. A panicking listener is restarted on the same
+// (still-open) fd instead of silently shrinking the accept pool.
+// Connection actors stay unsupervised bare spawns — per spec, a connection
+// is cheap and its failure is local: a 500 path, not a restart path.
+// (`spawn` from a listener parents the conn actor under that listener,
+// which never registers a supervisor channel, so conn deaths are invisible
+// to the pool supervisor by construction.)
+//
+// Shutdown sequence (drain-then-stop, the v0.2 chunk 2 decision):
+//   1. Set the shared shutdown flag. Every listener observes it at the
+//      top of its accept loop (parks are timed at LISTENER_TICK) and
+//      returns normally. Under `Restart::Transient` a normal exit is
+//      terminal, so no restart happens and the supervisor's active count
+//      drains to zero.
+//   2. Join the supervisor: `sup.run()` returns on its own once every
+//      listener has exited. The join is therefore the barrier "no new
+//      connections can ever be accepted" — listener fds are closed (the
+//      last Arc clones drop with the supervisor's ChildSpecs), and the
+//      kernel refuses new connects.
+//
+//      Why a flag and not `request_stop`: stopping pids that announce
+//      themselves races the spawn-to-registration gap (a fast shutdown
+//      CAN beat a fresh listener to the registry), and smarm's
+//      `request_stop` is lossy against a QUEUED actor that then parks
+//      without passing an observation point — found the hard way; see
+//      the chunk 2 commit message. The flag is wake-free and race-free.
+//   3. BeginDrain: the registry stops idle conns now and each remaining
+//      conn the moment it finishes its in-flight request.
+//   4. Poll until no conns remain or the drain deadline passes; past the
+//      deadline, ForceStopConns every tick until the set empties (a conn
+//      accepted just before listener death may register late).
+//   5. Root returns. `rt.run` itself returns only when every actor has
+//      exited (force-stopped conns unwind through their fd waits safely —
+//      smarm's 06-10 io fix — and close their sockets via OwnedFd::drop).
 
-pub fn serve_with(config: Config, pipeline: Pipeline) -> io::Result<()> {
+pub fn serve_with_shutdown(
+    config: Config,
+    pipeline: Pipeline,
+    signal: ShutdownSignal,
+) -> io::Result<()> {
     let listener = bind_and_listen(config.addr)?;
     println!("urus: listening on {}", config.addr);
 
-    // We want one connection-actor-spawning loop per listener pool slot.
-    // Each gets its own dup'd fd so epoll registrations don't collide.
+    // One connection-actor-spawning loop per listener pool slot. Each gets
+    // its own dup'd fd so epoll registrations don't collide. Each fd is
+    // owned by its ChildSpec's factory closure (via `Arc`): a restarted
+    // listener re-enters `accept`/`wait_readable` on the same fd — no
+    // re-dup, no window where the slot has no fd.
     let mut listener_fds = Vec::with_capacity(config.listener_pool);
-    listener_fds.push(listener); // primary keeps the original
+    listener_fds.push(Arc::new(listener)); // primary keeps the original
 
     for _ in 1..config.listener_pool {
         let dup = dup_fd(listener_fds[0].as_raw())?;
-        listener_fds.push(dup);
+        listener_fds.push(Arc::new(dup));
     }
 
     let limits        = config.to_conn_limits();
+    let drain_timeout = config.drain_timeout;
 
-    // smarm's runtime API: init(Config) then run(f). The closure is the
-    // root actor; from there we spawn one listener per fd in the pool.
     let smarm_cfg = match config.scheduler_threads {
         Some(n) => smarm::Config::exact(n),
         None    => smarm::Config::default(),
     };
     let rt = smarm::init(smarm_cfg);
+    // Listener self-termination flag — see the shutdown sequence below.
+    let shutdown_flag = Arc::new(AtomicBool::new(false));
+
     rt.run(move || {
-        let n = listener_fds.len();
-        let mut handles = Vec::with_capacity(n);
+        // Registry first: listeners and conns cast into it from birth.
+        let registry = conn_registry::start();
+
+        let mut sup = OneForOne::new().strategy(Strategy::OneForOne);
         for (i, lfd) in listener_fds.into_iter().enumerate() {
             let p = pipeline.clone();
-            let h = smarm::spawn(move || {
+            let r = registry.clone();
+            let sf = shutdown_flag.clone();
+            sup = sup.child(ChildSpec::new(Restart::Transient, move || {
                 println!("urus: listener {} starting", i);
-                listener_loop(lfd, p, limits);
-            });
-            handles.push(h);
+                // Named for whereis-style introspection. On a restart the
+                // old binding points at a dead pid; smarm's registry
+                // evicts stale bindings lazily, so re-registering the
+                // same name is fine. Ignore the result — a registry
+                // hiccup must not take the listener down.
+                let _ = smarm::register(
+                    format!("urus.listener.{i}"),
+                    smarm::self_pid(),
+                );
+                listener_loop(lfd.clone(), p.clone(), limits, r.clone(), sf.clone());
+            }));
         }
-        // Block forever (until ctrl-C) by joining the listeners. They
-        // never exit on their own in v1.
-        for h in handles {
-            let _ = h.join();
+        // Default intensity (3 per 5s) applies; a listener crash-looping
+        // faster than that trips the cap and tears the pool down — loud
+        // failure over a zombie server.
+        let sup_h = smarm::spawn(move || sup.run());
+        // Register via the JoinHandle's pid rather than inside the
+        // closure: the binding exists before the supervisor body runs a
+        // single instruction, so an early `whereis("urus.server")` can't
+        // race a None. Result ignored for the same reason as listeners.
+        let _ = smarm::register("urus.server", sup_h.pid());
+
+        // Block until told to shut down. We poll `try_recv` + `sleep`
+        // rather than parking in `recv`: a smarm `Sender::send` from a
+        // foreign OS thread (no runtime in its TLS) enqueues fine but its
+        // unpark is a `try_with_runtime` no-op — a parked receiver would
+        // never wake. The timer wake comes from inside the runtime, so the
+        // poll sees the message within one interval. (A cross-thread-safe
+        // unpark is a smarm roadmap candidate; this poll dies with it.)
+        // If every Handle was dropped the channel closes and no shutdown
+        // can ever arrive: serve forever, exactly v1's semantics.
+        loop {
+            match signal.rx.try_recv() {
+                Ok(Some(())) => break,
+                Ok(None)     => smarm::sleep(SHUTDOWN_POLL),
+                Err(_)       => smarm::sleep(Duration::from_secs(3600)),
             }
+        }
+
+        // ----- Shutdown. -----
+        // 1 + 2. Flag the listeners down and join the supervisor; the
+        //        join returns once every listener has exited normally
+        //        (Transient: normal exit is terminal). After this point
+        //        no connection can ever be accepted again.
+        shutdown_flag.store(true, Ordering::Relaxed);
+        let _ = sup_h.join();
+
+        // 3 + 4. Drain. Same sweep discipline as listeners on the force-
+        // stop path: a conn accepted just before its listener died may
+        // register after the deadline, so keep force-stopping until the
+        // set is empty (each pass kills everything registered; new
+        // registrants are a strictly shrinking population once listeners
+        // are gone).
+        let _ = registry.cast(Cast::BeginDrain);
+        let deadline = std::time::Instant::now() + drain_timeout;
+        let mut force = false;
+        loop {
+            match registry.call(Call::ConnCount) {
+                Ok(Reply::ConnCount(0)) => break,
+                Ok(_) => {}
+                Err(_) => break, // registry gone; nothing left to track
+            }
+            let now = std::time::Instant::now();
+            if force || now >= deadline {
+                force = true;
+                let _ = registry.cast(Cast::ForceStopConns);
+                smarm::sleep(Duration::from_millis(10));
+            } else {
+                smarm::sleep(Duration::from_millis(50).min(deadline - now));
+            }
+        }
+
+        // 5. Our ServerRef drops here. The registry's inbox closes once
+        //    the last conn's clone drops with it, and the runtime winds
+        //    down when the last actor exits.
     });
 
     Ok(())
 }
 
+// ---------------------------------------------------------------------------
+// serve_with / serve — convenience entries without a shutdown handle.
+// ---------------------------------------------------------------------------
+
+pub fn serve_with(config: Config, pipeline: Pipeline) -> io::Result<()> {
+    // The Handle is dropped immediately: shutdown can never be signalled
+    // and the server runs until externally killed (v1 semantics).
+    let (_handle, signal) = shutdown_handle();
+    serve_with_shutdown(config, pipeline, signal)
+}
+
 // ---------------------------------------------------------------------------
 // serve — convenience over serve_with.
 // ---------------------------------------------------------------------------

src/sse.rs

@@ -0,0 +1,178 @@
+//! Server-Sent Events sugar over `RespBody::Stream`.
+//!
+//! An SSE response is just a streaming body with the right headers and a
+//! heartbeat: `Conn::sse()` wires all of it and hands back an
+//! [`EventSender`] for a producer actor to feed.
+//!
+//! ```no_run
+//! use urus::{Conn, Next, Pipeline, Router};
+//! use std::time::Duration;
+//!
+//! let pipeline = Pipeline::new().plug(Router::new().get(
+//!     "/events",
+//!     |c: Conn, _n: Next| {
+//!         let (c, events) = c.sse();
+//!         smarm::spawn(move || {
+//!             let mut i = 0;
+//!             loop {
+//!                 if events.send("tick", &i.to_string()).is_err() {
+//!                     return; // client gone; conn actor dropped the stream
+//!                 }
+//!                 i += 1;
+//!                 smarm::sleep(Duration::from_secs(1));
+//!             }
+//!         });
+//!         c
+//!     },
+//! ));
+//! ```
+//!
+//! Liveness: the connection actor emits a `: keep-alive` comment chunk
+//! whenever [`HEARTBEAT_INTERVAL`] passes with no event (see
+//! `StreamBody::heartbeat`). A client that went away is detected when a
+//! write — event or heartbeat — stalls past `write_timeout`; the conn
+//! actor then drops the stream and the producer's next [`EventSender`]
+//! call returns `Err(SseClosed)`. There is no request clock on an SSE
+//! response: `request_timeout` covers only the read phase, by design.
+
+use crate::conn::{Conn, RespBody, StreamBody};
+
+use std::time::Duration;
+
+/// Default heartbeat: one comment line per this interval of silence.
+pub const HEARTBEAT_INTERVAL: Duration = Duration::from_secs(15);
+
+/// What the heartbeat puts on the wire — an SSE comment, invisible to
+/// `EventSource` consumers.
+pub(crate) const HEARTBEAT_PAYLOAD: &[u8] = b": keep-alive\n\n";
+
+/// The stream has ended: the connection actor dropped the receiving end
+/// (client disconnect, write timeout, or server shutdown). Producers
+/// should exit when they see this.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SseClosed;
+
+impl std::fmt::Display for SseClosed {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("SSE stream closed")
+    }
+}
+impl std::error::Error for SseClosed {}
+
+/// Producer handle for an SSE response. Clonable — multiple producers may
+/// feed one stream; the stream ends when the LAST clone drops.
+#[derive(Clone)]
+pub struct EventSender {
+    tx: smarm::Sender<Vec<u8>>,
+}
+
+impl EventSender {
+    /// Send a named event: `event: {event}` + `data:` line(s).
+    pub fn send(&self, event: &str, data: &str) -> Result<(), SseClosed> {
+        self.tx
+            .send(format_event(Some(event), data))
+            .map_err(|_| SseClosed)
+    }
+
+    /// Send an unnamed event (`data:` line(s) only) — what `EventSource`
+    /// surfaces as a plain `message`.
+    pub fn data(&self, data: &str) -> Result<(), SseClosed> {
+        self.tx
+            .send(format_event(None, data))
+            .map_err(|_| SseClosed)
+    }
+
+    /// Send a comment line. Invisible to `EventSource`; useful for
+    /// application-level pings beyond the built-in heartbeat.
+    pub fn comment(&self, text: &str) -> Result<(), SseClosed> {
+        let mut out = Vec::with_capacity(text.len() + 4);
+        out.extend_from_slice(b": ");
+        out.extend_from_slice(text.as_bytes());
+        out.extend_from_slice(b"\n\n");
+        self.tx.send(out).map_err(|_| SseClosed)
+    }
+}
+
+/// Wire format for one event. Multi-line `data` becomes one `data:` line
+/// per line (the SSE framing for embedded newlines); the blank line
+/// dispatches the event.
+pub(crate) fn format_event(event: Option<&str>, data: &str) -> Vec<u8> {
+    let mut out = Vec::with_capacity(data.len() + 32);
+    if let Some(e) = event {
+        out.extend_from_slice(b"event: ");
+        out.extend_from_slice(e.as_bytes());
+        out.push(b'\n');
+    }
+    for line in data.split('\n') {
+        out.extend_from_slice(b"data: ");
+        out.extend_from_slice(line.as_bytes());
+        out.push(b'\n');
+    }
+    out.push(b'\n');
+    out
+}
+
+impl Conn {
+    /// Turn this response into a Server-Sent Events stream with the
+    /// default [`HEARTBEAT_INTERVAL`]. Returns the `Conn` (return it from
+    /// the handler) and the [`EventSender`] to hand to a producer actor.
+    pub fn sse(self) -> (Self, EventSender) {
+        self.sse_with_heartbeat(HEARTBEAT_INTERVAL)
+    }
+
+    /// [`Conn::sse`] with a custom heartbeat interval.
+    pub fn sse_with_heartbeat(mut self, interval: Duration) -> (Self, EventSender) {
+        let (tx, rx) = smarm::channel::<Vec<u8>>();
+        if self.status.is_none() {
+            self.status = Some(200);
+        }
+        self.resp_headers.set("content-type", "text/event-stream");
+        self.resp_headers.set("cache-control", "no-cache");
+        self.resp_body = RespBody::Stream(
+            StreamBody::new(rx).with_heartbeat(interval, HEARTBEAT_PAYLOAD.to_vec()),
+        );
+        (self, EventSender { tx })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn format_named_event() {
+        assert_eq!(
+            format_event(Some("tick"), "42"),
+            b"event: tick\ndata: 42\n\n".to_vec()
+        );
+    }
+
+    #[test]
+    fn format_unnamed_event() {
+        assert_eq!(format_event(None, "hi"), b"data: hi\n\n".to_vec());
+    }
+
+    #[test]
+    fn format_multiline_data() {
+        assert_eq!(
+            format_event(None, "a\nb"),
+            b"data: a\ndata: b\n\n".to_vec()
+        );
+    }
+
+    #[test]
+    fn sse_sets_headers_and_stream_body() {
+        let (conn, _events) = Conn::new().sse();
+        assert_eq!(conn.status, Some(200));
+        assert_eq!(conn.resp_headers.get("content-type"), Some("text/event-stream"));
+        assert_eq!(conn.resp_headers.get("cache-control"), Some("no-cache"));
+        match &conn.resp_body {
+            RespBody::Stream(s) => {
+                let (interval, payload) = s.heartbeat.as_ref().expect("heartbeat set");
+                assert_eq!(*interval, HEARTBEAT_INTERVAL);
+                assert_eq!(payload.as_slice(), HEARTBEAT_PAYLOAD);
+            }
+            other => panic!("expected Stream body, got {other:?}"),
+        }
+    }
+}

src/ws/duplex.rs

@@ -0,0 +1,424 @@
+//! The WebSocket duplex loop — v0.4 chunk 3.
+//!
+//! After an accepted upgrade the connection actor calls [`run_duplex`],
+//! which replaces the HTTP request loop for the rest of the socket's
+//! life. ONE actor speaks both directions (the v0.4 topology decision):
+//! each iteration parks on a two-arm select —
+//!
+//!   try_select(&[&outbound_rx, &FdArm::readable(fd)])
+//!
+//! — smarm's RFC 008 fd arms composed with a channel arm on one wait
+//! epoch; urus is deliberately the first consumer of that machinery.
+//! The outbound arm sits at index 0 (select is priority-ordered): owed
+//! writes drain before we read more, which is honest backpressure.
+//! Accepted gap, by design: while a large outbound frame is mid-write
+//! the actor isn't reading, so a ping arriving during that write is
+//! answered after it completes.
+//!
+//! Handler model (the v0.4 chunk-3 decisions, mirroring SSE):
+//! - [`WsHandler`] callbacks run IN the connection actor, inside the
+//!   select loop. A slow `on_message` stops reads — backpressure, not a
+//!   bug. Handlers needing concurrency spawn their own actor and hand it
+//!   a [`WsSender`] clone, exactly like an SSE producer.
+//! - [`WsSender`] is the clonable outbound handle; every method returns
+//!   `Err(WsClosed)` once the connection is gone.
+//! - Control frames are invisible to the handler in v1: pings are
+//!   auto-ponged (RFC 6455 §5.5.2 MUST), pongs are absorbed, a peer
+//!   close is auto-echoed (§5.5.1) and surfaces only as `on_close`.
+//!   `on_ping`/`on_pong` hooks can land later as default trait methods
+//!   without breaking anyone.
+//!
+//! Liveness mirrors SSE: there is no request clock on an open
+//! WebSocket. An idle connection parks in the select (stoppable by a
+//! draining registry — graceful shutdown force-stops it at the drain
+//! deadline); a dead client is caught when a write stalls past
+//! `write_timeout`. Reads have no deadline of their own — the select
+//! only wakes the read path when bytes are pending.
+
+use crate::conn_actor::{read_some, write_all, ConnLimits};
+use crate::ws::frame::{self, Assembler, Frame, FrameError, Message, Opcode};
+
+use smarm::FdArm;
+
+use std::os::fd::RawFd;
+use std::time::Instant;
+
+// ---------------------------------------------------------------------------
+// Handler trait
+// ---------------------------------------------------------------------------
+
+/// Application callbacks for an upgraded WebSocket connection. Both run
+/// inside the connection actor's select loop — see the module docs for
+/// what that implies (backpressure, spawn-for-concurrency).
+///
+/// A panic in `on_message` closes the connection with a `1011 internal
+/// error` close frame and skips `on_close` (the handler is not re-entered
+/// after it panicked).
+pub trait WsHandler: Send + 'static {
+    /// The connection is up: the 101 has been written and the frame loop
+    /// is about to start. Runs exactly once, first, inside the
+    /// connection actor. This is the place to subscribe / spawn
+    /// producers for sessions where the client may never send (a
+    /// listen-only chat member, a live feed) — `on_message` never fires
+    /// for those. NOTE the 101 reaches the client *before* `on_open`
+    /// runs: a client that needs to know its subscriptions are live must
+    /// use an application-level ack (send something, await the reply —
+    /// any reply proves `on_open` completed, since callbacks are
+    /// sequential in the conn actor). A panic here closes `1011` and
+    /// skips `on_close`, exactly like a panicking `on_message`.
+    /// Default: no-op.
+    fn on_open(&mut self, sender: &WsSender) {
+        let _ = sender;
+    }
+
+    /// A complete data message (fragments already reassembled, text
+    /// already UTF-8 validated) arrived from the client.
+    fn on_message(&mut self, msg: Message, sender: &WsSender);
+
+    /// The connection is over. `code`/`reason` are what the PEER said:
+    /// `Some` iff a close frame was received from the client (whether it
+    /// initiated or echoed ours); `None` for everything wordless — EOF,
+    /// write failure, or a close handshake that timed out. Called exactly
+    /// once, last, on every exit path except a handler panic or a
+    /// force-stop unwind.
+    fn on_close(&mut self, code: Option<u16>, reason: &str) {
+        let _ = (code, reason);
+    }
+}
+
+// ---------------------------------------------------------------------------
+// WsSender — the clonable outbound handle
+// ---------------------------------------------------------------------------
+
+/// The connection is gone (client disconnect, write timeout, close
+/// handshake completed, or server shutdown). Producers should exit when
+/// they see this — the exact contract of `SseClosed`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct WsClosed;
+
+impl std::fmt::Display for WsClosed {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("WebSocket connection closed")
+    }
+}
+impl std::error::Error for WsClosed {}
+
+pub(crate) enum Outbound {
+    Msg(Message),
+    Ping,
+    Close(u16, String),
+}
+
+/// Outbound handle for an upgraded connection. Clonable — hand copies to
+/// producer actors freely; the connection outlives none of them (sends
+/// after it ends return `Err(WsClosed)`).
+///
+/// v1 sends each message as a single unfragmented frame; outbound
+/// fragmentation is not implemented.
+#[derive(Clone)]
+pub struct WsSender {
+    pub(crate) tx: smarm::Sender<Outbound>,
+}
+
+impl WsSender {
+    /// Queue a data message for the client.
+    pub fn send(&self, msg: Message) -> Result<(), WsClosed> {
+        self.tx.send(Outbound::Msg(msg)).map_err(|_| WsClosed)
+    }
+
+    /// Sugar: queue a text message.
+    pub fn text(&self, s: impl Into<String>) -> Result<(), WsClosed> {
+        self.send(Message::Text(s.into()))
+    }
+
+    /// Sugar: queue a binary message.
+    pub fn binary(&self, b: impl Into<Vec<u8>>) -> Result<(), WsClosed> {
+        self.send(Message::Binary(b.into()))
+    }
+
+    /// Queue a ping (empty payload). Application-level liveness beyond
+    /// the built-in write-timeout detection; the pong is absorbed by the
+    /// loop in v1.
+    pub fn ping(&self) -> Result<(), WsClosed> {
+        self.tx.send(Outbound::Ping).map_err(|_| WsClosed)
+    }
+
+    /// Initiate the close handshake: a close frame with `code`/`reason`
+    /// goes out, the loop then waits (bounded by `write_timeout`) for the
+    /// peer's echo before dropping the socket. `reason` is truncated to
+    /// fit the 125-byte control payload on a char boundary.
+    pub fn close(&self, code: u16, reason: &str) -> Result<(), WsClosed> {
+        self.tx
+            .send(Outbound::Close(code, reason.to_string()))
+            .map_err(|_| WsClosed)
+    }
+}
+
+// ---------------------------------------------------------------------------
+// The loop
+// ---------------------------------------------------------------------------
+
+/// Run the duplex loop until the connection ends. `buf` carries any bytes
+/// already read past the upgrade request's head — a client may pipeline
+/// its first frame behind the handshake, and those bytes belong to us
+/// now.
+pub(crate) fn run_duplex(
+    raw: RawFd,
+    mut buf: Vec<u8>,
+    mut handler: Box<dyn WsHandler>,
+    limits: &ConnLimits,
+) {
+    let (tx, rx) = smarm::channel::<Outbound>();
+    // We hold this sender for handler callbacks, so the rx arm can never
+    // report closed while the loop runs — no closed-arm starvation case.
+    let sender = WsSender { tx };
+    let mut asm = Assembler::new(limits.max_message_bytes);
+
+    // on_open before anything is decoded — even a pipelined first frame
+    // is observed by a handler that knows the connection exists. Same
+    // panic contract as on_message: re-raise a stop sentinel, else 1011.
+    let r = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| handler.on_open(&sender)));
+    if r.is_err() {
+        smarm::preempt::check_cancelled();
+        let _ = close_and_drain_code(raw, 1011, "", &mut buf, limits);
+        return;
+    }
+
+    loop {
+        // ----- 1. Decode everything already buffered. -----
+        // Runs before the first select so a pipelined first frame is
+        // served without waiting for fresh readability.
+        loop {
+            let (frame, consumed) =
+                match frame::decode(&buf, true, limits.max_frame_payload) {
+                    Ok(Some(hit)) => hit,
+                    Ok(None) => break, // incomplete; need more bytes
+                    Err(e) => {
+                        let peer = close_and_drain(raw, e, &mut buf, limits);
+                        finish(&mut handler, peer);
+                        return;
+                    }
+                };
+            buf.drain(..consumed);
+
+            match frame.opcode {
+                Opcode::Ping => {
+                    // §5.5.2 MUST pong, payload echoed. Written inline —
+                    // "as soon as practical" beats channel ordering.
+                    let pong = Frame::new(Opcode::Pong, frame.payload);
+                    if write_frame(raw, &pong, limits).is_err() {
+                        finish(&mut handler, None);
+                        return;
+                    }
+                }
+                Opcode::Pong => {} // invisible in v1
+                Opcode::Close => {
+                    // Peer-initiated close: echo its status code (§5.5.1)
+                    // and end. The server side closes the TCP connection
+                    // first by design (§7.1.1 puts that burden on us).
+                    let echo_payload =
+                        frame.payload.get(..2).map(<[u8]>::to_vec).unwrap_or_default();
+                    let peer = match frame::parse_close_payload(&frame.payload) {
+                        Ok(cp) => {
+                            let _ = write_frame(
+                                raw,
+                                &Frame::new(Opcode::Close, echo_payload),
+                                limits,
+                            );
+                            cp
+                        }
+                        Err(e) => {
+                            // Malformed close payload: answer with the
+                            // mapped code instead of an echo.
+                            let _ = write_frame(
+                                raw,
+                                &Frame::new(
+                                    Opcode::Close,
+                                    frame::close_payload(e.close_code(), ""),
+                                ),
+                                limits,
+                            );
+                            None
+                        }
+                    };
+                    finish_with(&mut handler, peer);
+                    return;
+                }
+                _ => match asm.push(frame) {
+                    Ok(Some(msg)) => {
+                        // A panicking handler must not swallow smarm's stop
+                        // sentinel — same re-raise dance as the pipeline.
+                        let r = std::panic::catch_unwind(
+                            std::panic::AssertUnwindSafe(|| {
+                                handler.on_message(msg, &sender)
+                            }),
+                        );
+                        if r.is_err() {
+                            smarm::preempt::check_cancelled();
+                            // Genuine handler panic: 1011 out, no further
+                            // handler calls (no on_close).
+                            let _ = close_and_drain_code(
+                                raw, 1011, "", &mut buf, limits,
+                            );
+                            return;
+                        }
+                    }
+                    Ok(None) => {} // mid-fragmentation
+                    Err(e) => {
+                        let peer = close_and_drain(raw, e, &mut buf, limits);
+                        finish(&mut handler, peer);
+                        return;
+                    }
+                },
+            }
+        }
+
+        // ----- 2. Park on first-of outbound / fd-readable. -----
+        // Outbound at index 0: select is priority-ordered, so owed writes
+        // go out before we read more. try_select over select: an fd-arm
+        // registration failure (EBADF after a peer RST, EMFILE on the
+        // epoll set) is a connection event, not a crash. NOTE from the
+        // RFC 008 review: an `AlreadyExists` here would mean a stale
+        // waiter survived select's eager cleanup — that is a smarm bug
+        // candidate; capture it with --features smarm-trace and report,
+        // do not paper over.
+        let fd_arm = FdArm::readable(raw);
+        let idx = match smarm::try_select(&[&rx, &fd_arm]) {
+            Ok(i) => i,
+            Err(_) => {
+                finish(&mut handler, None);
+                return;
+            }
+        };
+
+        if idx == 0 {
+            // Outbound arm won. Single receiver + we hold a sender: a
+            // ready arm means a message is queued (Empty/closed are
+            // impossible here, but stay defensive).
+            let Ok(Some(out)) = rx.try_recv() else { continue };
+            match out {
+                Outbound::Msg(msg) => {
+                    let f = match msg {
+                        Message::Text(s) => Frame::new(Opcode::Text, s.into_bytes()),
+                        Message::Binary(b) => Frame::new(Opcode::Binary, b),
+                    };
+                    if write_frame(raw, &f, limits).is_err() {
+                        finish(&mut handler, None);
+                        return;
+                    }
+                }
+                Outbound::Ping => {
+                    let f = Frame::new(Opcode::Ping, Vec::new());
+                    if write_frame(raw, &f, limits).is_err() {
+                        finish(&mut handler, None);
+                        return;
+                    }
+                }
+                Outbound::Close(code, reason) => {
+                    // We initiate: close out, bounded wait for the echo.
+                    let peer = close_and_drain_code(raw, code, &reason, &mut buf, limits);
+                    finish(&mut handler, peer);
+                    return;
+                }
+            }
+        } else {
+            // Readable. The deadline is nominal — the fd already reported
+            // ready, this returns without a fresh park in practice.
+            match read_some(
+                raw,
+                &mut buf,
+                limits.initial_read_buf,
+                Instant::now() + limits.write_timeout,
+            ) {
+                Ok(0) => {
+                    // EOF without a close frame: abnormal but common.
+                    finish(&mut handler, None);
+                    return;
+                }
+                Ok(_) => {}
+                Err(_) => {
+                    finish(&mut handler, None);
+                    return;
+                }
+            }
+        }
+    }
+}
+
+/// `on_close(None, "")` — wordless endings (EOF, write failure, errors).
+fn finish(handler: &mut Box<dyn WsHandler>, peer: Option<(u16, String)>) {
+    finish_with(handler, peer);
+}
+
+/// `on_close` with whatever the peer said, panic-shielded like
+/// `on_message` (stop sentinel re-raised; a panic here just ends the
+/// already-ending connection).
+fn finish_with(handler: &mut Box<dyn WsHandler>, peer: Option<(u16, String)>) {
+    let r = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
+        match &peer {
+            Some((code, reason)) => handler.on_close(Some(*code), reason),
+            None => handler.on_close(None, ""),
+        }
+    }));
+    if r.is_err() {
+        smarm::preempt::check_cancelled();
+    }
+}
+
+/// One frame onto the wire under a fresh `write_timeout` budget — the
+/// streaming-chunk discipline, verbatim.
+fn write_frame(raw: RawFd, f: &Frame, limits: &ConnLimits) -> std::io::Result<()> {
+    write_all(raw, &f.encode(), Instant::now() + limits.write_timeout)
+}
+
+/// Server-initiated close for a frame/assembly error: map to the §7.4
+/// code and run the handshake tail.
+fn close_and_drain(
+    raw: RawFd,
+    e: FrameError,
+    buf: &mut Vec<u8>,
+    limits: &ConnLimits,
+) -> Option<(u16, String)> {
+    close_and_drain_code(raw, e.close_code(), "", buf, limits)
+}
+
+/// Write our close frame, then wait — bounded by ONE `write_timeout`
+/// budget — for the peer's close frame, discarding data frames (§1.4: an
+/// endpoint that has sent close may discard incoming data). Returns what
+/// the peer's close said, `None` if it never arrived (EOF, timeout,
+/// garbage). The socket drops at the caller either way.
+fn close_and_drain_code(
+    raw: RawFd,
+    code: u16,
+    reason: &str,
+    buf: &mut Vec<u8>,
+    limits: &ConnLimits,
+) -> Option<(u16, String)> {
+    let ours = Frame::new(Opcode::Close, frame::close_payload(code, reason));
+    if write_frame(raw, &ours, limits).is_err() {
+        return None;
+    }
+
+    let deadline = Instant::now() + limits.write_timeout;
+    loop {
+        loop {
+            match frame::decode(buf, true, limits.max_frame_payload) {
+                Ok(Some((frame, consumed))) => {
+                    buf.drain(..consumed);
+                    if frame.opcode == Opcode::Close {
+                        return frame::parse_close_payload(&frame.payload)
+                            .ok()
+                            .flatten();
+                    }
+                    // Data/ping mid-handshake: discarded.
+                }
+                Ok(None) => break,
+                Err(_) => return None, // garbage during the tail: give up
+            }
+        }
+        match read_some(raw, buf, limits.initial_read_buf, deadline) {
+            Ok(0) | Err(_) => return None,
+            Ok(_) => {}
+        }
+    }
+}

src/ws/frame.rs

@@ -0,0 +1,637 @@
+//! RFC 6455 §5 — the frame codec. Pure: bytes in, frames out, no io and
+//! no actor machinery, so every edge lives in fast unit tests. The
+//! connection actor (chunk 3) owns buffering and the socket.
+//!
+//! Server-side rules enforced here:
+//! - client→server frames MUST be masked (§5.1); decode takes
+//!   `require_masked` so a future client mode can reuse the codec.
+//! - server→client frames are NEVER masked; [`Frame::encode`] doesn't
+//!   offer masking. [`encode_masked`] exists for the client side of
+//!   tests.
+//! - RSV bits must be 0 (we negotiate no extensions), §5.2.
+//! - Payload lengths must use the minimal encoding, §5.2.
+//! - Control frames: FIN set, payload ≤ 125, §5.5.
+//!
+//! Errors map to close codes via [`FrameError::close_code`]: protocol
+//! violations → 1002, oversize → 1009, bad UTF-8 in text → 1007.
+
+/// §5.2 opcodes. Reserved values are rejected at decode.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Opcode {
+    Continuation,
+    Text,
+    Binary,
+    Close,
+    Ping,
+    Pong,
+}
+
+impl Opcode {
+    fn from_u4(n: u8) -> Option<Self> {
+        Some(match n {
+            0x0 => Opcode::Continuation,
+            0x1 => Opcode::Text,
+            0x2 => Opcode::Binary,
+            0x8 => Opcode::Close,
+            0x9 => Opcode::Ping,
+            0xA => Opcode::Pong,
+            _ => return None,
+        })
+    }
+
+    fn to_u4(self) -> u8 {
+        match self {
+            Opcode::Continuation => 0x0,
+            Opcode::Text => 0x1,
+            Opcode::Binary => 0x2,
+            Opcode::Close => 0x8,
+            Opcode::Ping => 0x9,
+            Opcode::Pong => 0xA,
+        }
+    }
+
+    pub fn is_control(self) -> bool {
+        matches!(self, Opcode::Close | Opcode::Ping | Opcode::Pong)
+    }
+}
+
+/// One decoded frame; payload already unmasked.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Frame {
+    pub fin: bool,
+    pub opcode: Opcode,
+    pub payload: Vec<u8>,
+}
+
+impl Frame {
+    pub fn new(opcode: Opcode, payload: impl Into<Vec<u8>>) -> Self {
+        Frame { fin: true, opcode, payload: payload.into() }
+    }
+
+    /// Serialise unmasked (server→client, §5.1: a server MUST NOT mask).
+    pub fn encode(&self) -> Vec<u8> {
+        let mut out = Vec::with_capacity(self.payload.len() + 10);
+        encode_head(&mut out, self.fin, self.opcode, self.payload.len(), None);
+        out.extend_from_slice(&self.payload);
+        out
+    }
+}
+
+/// Why decoding (or assembly) failed. Fatal for the connection: the ws
+/// close handshake should carry [`FrameError::close_code`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum FrameError {
+    /// §5.x violation; the str is a debugging breadcrumb, not protocol.
+    Protocol(&'static str),
+    /// Frame or assembled message exceeds the configured cap → 1009.
+    TooLarge,
+    /// A complete text message that is not valid UTF-8 → 1007.
+    BadUtf8,
+}
+
+impl FrameError {
+    pub fn close_code(self) -> u16 {
+        match self {
+            FrameError::Protocol(_) => 1002,
+            FrameError::TooLarge => 1009,
+            FrameError::BadUtf8 => 1007,
+        }
+    }
+}
+
+/// Try to decode one frame from the front of `buf`.
+///
+/// - `Ok(Some((frame, consumed)))` — drop `consumed` bytes off the front.
+/// - `Ok(None)` — incomplete; read more. (Header-derived sizes are still
+///   bounds-checked first, so a hostile 8-byte length can't make the
+///   caller buffer toward it: oversize fails *before* the payload
+///   arrives.)
+/// - `Err(_)` — fatal; start the close handshake with the mapped code.
+pub fn decode(
+    buf: &[u8],
+    require_masked: bool,
+    max_payload: usize,
+) -> Result<Option<(Frame, usize)>, FrameError> {
+    if buf.len() < 2 {
+        return Ok(None);
+    }
+    let b0 = buf[0];
+    let b1 = buf[1];
+
+    let fin = b0 & 0x80 != 0;
+    if b0 & 0x70 != 0 {
+        return Err(FrameError::Protocol("RSV bits set without extension"));
+    }
+    let opcode = Opcode::from_u4(b0 & 0x0F)
+        .ok_or(FrameError::Protocol("reserved opcode"))?;
+
+    let masked = b1 & 0x80 != 0;
+    if require_masked && !masked {
+        return Err(FrameError::Protocol("unmasked client frame"));
+    }
+
+    if opcode.is_control() {
+        if !fin {
+            return Err(FrameError::Protocol("fragmented control frame"));
+        }
+        if b1 & 0x7F > 125 {
+            return Err(FrameError::Protocol("control payload > 125"));
+        }
+    }
+
+    // Payload length: 7-bit, or 126 + u16, or 127 + u64 — minimal form
+    // required (§5.2).
+    let (len, mut pos): (u64, usize) = match b1 & 0x7F {
+        126 => {
+            if buf.len() < 4 {
+                return Ok(None);
+            }
+            let l = u16::from_be_bytes([buf[2], buf[3]]) as u64;
+            if l < 126 {
+                return Err(FrameError::Protocol("non-minimal 16-bit length"));
+            }
+            (l, 4)
+        }
+        127 => {
+            if buf.len() < 10 {
+                return Ok(None);
+            }
+            let l = u64::from_be_bytes(buf[2..10].try_into().unwrap());
+            if l & (1 << 63) != 0 {
+                return Err(FrameError::Protocol("64-bit length MSB set"));
+            }
+            if l < 65536 {
+                return Err(FrameError::Protocol("non-minimal 64-bit length"));
+            }
+            (l, 10)
+        }
+        n => (n as u64, 2),
+    };
+
+    // Cap check BEFORE waiting for the payload (see decode docs).
+    if len > max_payload as u64 {
+        return Err(FrameError::TooLarge);
+    }
+    let len = len as usize;
+
+    let mask_key: Option<[u8; 4]> = if masked {
+        if buf.len() < pos + 4 {
+            return Ok(None);
+        }
+        let k = [buf[pos], buf[pos + 1], buf[pos + 2], buf[pos + 3]];
+        pos += 4;
+        Some(k)
+    } else {
+        None
+    };
+
+    if buf.len() < pos + len {
+        return Ok(None);
+    }
+
+    let mut payload = buf[pos..pos + len].to_vec();
+    if let Some(key) = mask_key {
+        for (i, b) in payload.iter_mut().enumerate() {
+            *b ^= key[i & 3];
+        }
+    }
+
+    Ok(Some((Frame { fin, opcode, payload }, pos + len)))
+}
+
+fn encode_head(
+    out: &mut Vec<u8>,
+    fin: bool,
+    opcode: Opcode,
+    len: usize,
+    mask: Option<[u8; 4]>,
+) {
+    let mask_bit = if mask.is_some() { 0x80 } else { 0 };
+    out.push(if fin { 0x80 } else { 0 } | opcode.to_u4());
+    if len <= 125 {
+        out.push(mask_bit | len as u8);
+    } else if len <= u16::MAX as usize {
+        out.push(mask_bit | 126);
+        out.extend_from_slice(&(len as u16).to_be_bytes());
+    } else {
+        out.push(mask_bit | 127);
+        out.extend_from_slice(&(len as u64).to_be_bytes());
+    }
+    if let Some(k) = mask {
+        out.extend_from_slice(&k);
+    }
+}
+
+/// Client-side serialisation (masked). Servers never call this in
+/// production — it exists so tests (and an eventual client mode) can
+/// produce conformant client frames.
+pub fn encode_masked(frame: &Frame, key: [u8; 4]) -> Vec<u8> {
+    let mut out = Vec::with_capacity(frame.payload.len() + 14);
+    encode_head(&mut out, frame.fin, frame.opcode, frame.payload.len(), Some(key));
+    out.extend(frame.payload.iter().enumerate().map(|(i, b)| b ^ key[i & 3]));
+    out
+}
+
+// ---------------------------------------------------------------------------
+// Close payload (§5.5.1, §7.4)
+// ---------------------------------------------------------------------------
+
+/// Parse a close frame payload: empty is fine (`None`); otherwise a
+/// 2-byte code + optional UTF-8 reason. A 1-byte payload, an invalid
+/// wire code, or a non-UTF-8 reason are protocol errors.
+pub fn parse_close_payload(payload: &[u8]) -> Result<Option<(u16, String)>, FrameError> {
+    match payload.len() {
+        0 => Ok(None),
+        1 => Err(FrameError::Protocol("1-byte close payload")),
+        _ => {
+            let code = u16::from_be_bytes([payload[0], payload[1]]);
+            if !close_code_valid_on_wire(code) {
+                return Err(FrameError::Protocol("invalid close code"));
+            }
+            let reason = std::str::from_utf8(&payload[2..])
+                .map_err(|_| FrameError::Protocol("close reason not UTF-8"))?;
+            Ok(Some((code, reason.to_string())))
+        }
+    }
+}
+
+/// §7.4.1/.2: codes an endpoint may put on the wire. 1004 is reserved;
+/// 1005/1006/1015 are signalling-only (MUST NOT appear in a close
+/// frame); 1000–1011 otherwise fine; 3000–4999 are app/registry space.
+fn close_code_valid_on_wire(code: u16) -> bool {
+    matches!(code, 1000..=1003 | 1007..=1011 | 3000..=4999)
+}
+
+/// Build a close frame payload for `code` (+ optional reason, truncated
+/// to fit the 125-byte control cap on a UTF-8 boundary).
+pub fn close_payload(code: u16, reason: &str) -> Vec<u8> {
+    let mut p = Vec::with_capacity(2 + reason.len().min(123));
+    p.extend_from_slice(&code.to_be_bytes());
+    let mut cut = reason.len().min(123);
+    while !reason.is_char_boundary(cut) {
+        cut -= 1;
+    }
+    p.extend_from_slice(&reason.as_bytes()[..cut]);
+    p
+}
+
+// ---------------------------------------------------------------------------
+// Message assembly (§5.4 fragmentation)
+// ---------------------------------------------------------------------------
+
+/// A complete application message.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Message {
+    Text(String),
+    Binary(Vec<u8>),
+}
+
+/// Reassembles data frames into [`Message`]s. Feed it ONLY data frames
+/// (Text/Binary/Continuation) — control frames interleave at the caller
+/// (§5.4 allows them mid-fragmentation) and never enter the assembler.
+///
+/// Enforced here: continuation with nothing in progress; a new data
+/// frame while a fragmented message is in progress; total message size
+/// (1009); text UTF-8 validity, checked once on the complete message
+/// (we deliver whole messages, so per-frame incremental validation buys
+/// nothing).
+#[derive(Debug)]
+pub struct Assembler {
+    buf: Vec<u8>,
+    in_progress: Option<Opcode>, // Text or Binary
+    max_message: usize,
+}
+
+impl Assembler {
+    pub fn new(max_message: usize) -> Self {
+        Assembler { buf: Vec::new(), in_progress: None, max_message }
+    }
+
+    pub fn push(&mut self, frame: Frame) -> Result<Option<Message>, FrameError> {
+        match (frame.opcode, self.in_progress) {
+            (Opcode::Text | Opcode::Binary, Some(_)) => {
+                return Err(FrameError::Protocol("new data frame mid-fragmentation"));
+            }
+            (Opcode::Continuation, None) => {
+                return Err(FrameError::Protocol("continuation without a message"));
+            }
+            (Opcode::Text | Opcode::Binary, None) if frame.fin => {
+                // Unfragmented fast path: no buffer copy.
+                if frame.payload.len() > self.max_message {
+                    return Err(FrameError::TooLarge);
+                }
+                return Self::complete(frame.opcode, frame.payload).map(Some);
+            }
+            (Opcode::Text | Opcode::Binary, None) => {
+                self.in_progress = Some(frame.opcode);
+            }
+            (Opcode::Continuation, Some(_)) => {}
+            (op, _) if op.is_control() => {
+                return Err(FrameError::Protocol("control frame fed to assembler"));
+            }
+            _ => unreachable!(),
+        }
+
+        if self.buf.len() + frame.payload.len() > self.max_message {
+            self.reset();
+            return Err(FrameError::TooLarge);
+        }
+        self.buf.extend_from_slice(&frame.payload);
+
+        if frame.fin {
+            let kind = self.in_progress.take().expect("checked above");
+            let payload = std::mem::take(&mut self.buf);
+            return Self::complete(kind, payload).map(Some);
+        }
+        Ok(None)
+    }
+
+    fn complete(kind: Opcode, payload: Vec<u8>) -> Result<Message, FrameError> {
+        match kind {
+            Opcode::Binary => Ok(Message::Binary(payload)),
+            Opcode::Text => String::from_utf8(payload)
+                .map(Message::Text)
+                .map_err(|_| FrameError::BadUtf8),
+            _ => unreachable!(),
+        }
+    }
+
+    fn reset(&mut self) {
+        self.buf.clear();
+        self.in_progress = None;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const MAX: usize = 1 << 20;
+
+    fn dec(buf: &[u8]) -> Result<Option<(Frame, usize)>, FrameError> {
+        decode(buf, true, MAX)
+    }
+
+    // ----- §5.7 worked examples. -----
+
+    #[test]
+    fn rfc_masked_hello() {
+        // "A single-frame masked text message" containing "Hello".
+        let wire = [0x81, 0x85, 0x37, 0xfa, 0x21, 0x3d, 0x7f, 0x9f, 0x4d, 0x51, 0x58];
+        let (f, used) = dec(&wire).unwrap().unwrap();
+        assert_eq!(used, wire.len());
+        assert!(f.fin);
+        assert_eq!(f.opcode, Opcode::Text);
+        assert_eq!(f.payload, b"Hello");
+    }
+
+    #[test]
+    fn rfc_unmasked_hello_rejected_then_allowed() {
+        let wire = [0x81, 0x05, b'H', b'e', b'l', b'l', b'o'];
+        assert_eq!(
+            dec(&wire),
+            Err(FrameError::Protocol("unmasked client frame"))
+        );
+        // Same bytes are fine when masking isn't required (client mode).
+        let (f, _) = decode(&wire, false, MAX).unwrap().unwrap();
+        assert_eq!(f.payload, b"Hello");
+    }
+
+    #[test]
+    fn rfc_fragmented_hel_lo() {
+        let f1 = [0x01, 0x03, b'H', b'e', b'l'];
+        let f2 = [0x80, 0x02, b'l', b'o'];
+        let (a, _) = decode(&f1, false, MAX).unwrap().unwrap();
+        let (b, _) = decode(&f2, false, MAX).unwrap().unwrap();
+        assert!(!a.fin);
+        assert_eq!(a.opcode, Opcode::Text);
+        assert_eq!(b.opcode, Opcode::Continuation);
+
+        let mut asm = Assembler::new(MAX);
+        assert_eq!(asm.push(a).unwrap(), None);
+        assert_eq!(
+            asm.push(b).unwrap(),
+            Some(Message::Text("Hello".into()))
+        );
+    }
+
+    #[test]
+    fn rfc_ping_pong_hello() {
+        let ping = [0x89, 0x05, b'H', b'e', b'l', b'l', b'o'];
+        let (f, _) = decode(&ping, false, MAX).unwrap().unwrap();
+        assert_eq!(f.opcode, Opcode::Ping);
+        assert_eq!(f.payload, b"Hello");
+        // Pong response carries the same payload back, unmasked.
+        let pong = Frame::new(Opcode::Pong, f.payload.clone()).encode();
+        assert_eq!(pong, [0x8A, 0x05, b'H', b'e', b'l', b'l', b'o']);
+    }
+
+    #[test]
+    fn rfc_256_bytes_binary_16bit_len() {
+        let payload = vec![0xAB; 256];
+        let wire = Frame::new(Opcode::Binary, payload.clone()).encode();
+        assert_eq!(&wire[..4], &[0x82, 0x7E, 0x01, 0x00]);
+        let (f, used) = decode(&wire, false, MAX).unwrap().unwrap();
+        assert_eq!(used, wire.len());
+        assert_eq!(f.payload, payload);
+    }
+
+    #[test]
+    fn rfc_64k_binary_64bit_len() {
+        let payload = vec![7u8; 65536];
+        let wire = Frame::new(Opcode::Binary, payload.clone()).encode();
+        assert_eq!(&wire[..10], &[0x82, 0x7F, 0, 0, 0, 0, 0, 1, 0, 0]);
+        let (f, _) = decode(&wire, false, MAX).unwrap().unwrap();
+        assert_eq!(f.payload.len(), 65536);
+    }
+
+    // ----- round trips. -----
+
+    #[test]
+    fn masked_roundtrip_all_lengths() {
+        // Cross the 125/126 and 65535/65536 encoding boundaries.
+        for len in [0, 1, 125, 126, 127, 65535, 65536] {
+            let f = Frame::new(Opcode::Binary, vec![0x5A; len]);
+            let wire = encode_masked(&f, [0xDE, 0xAD, 0xBE, 0xEF]);
+            let (g, used) = decode(&wire, true, 1 << 20).unwrap().unwrap();
+            assert_eq!(used, wire.len(), "len {len}");
+            assert_eq!(g, f, "len {len}");
+        }
+    }
+
+    #[test]
+    fn decode_is_incremental_at_every_prefix() {
+        let f = Frame::new(Opcode::Text, b"incremental".to_vec());
+        let wire = encode_masked(&f, [1, 2, 3, 4]);
+        for cut in 0..wire.len() {
+            assert_eq!(dec(&wire[..cut]).unwrap(), None, "prefix {cut}");
+        }
+        assert!(dec(&wire).unwrap().is_some());
+    }
+
+    #[test]
+    fn decode_leaves_trailing_bytes() {
+        let f = Frame::new(Opcode::Text, b"a".to_vec());
+        let mut wire = encode_masked(&f, [9, 9, 9, 9]);
+        let first_len = wire.len();
+        wire.extend_from_slice(&[0x81]); // start of a second frame
+        let (_, used) = dec(&wire).unwrap().unwrap();
+        assert_eq!(used, first_len);
+    }
+
+    // ----- protocol violations. -----
+
+    #[test]
+    fn rsv_bits_rejected() {
+        for rsv in [0x40, 0x20, 0x10] {
+            let wire = [0x81 | rsv, 0x80, 0, 0, 0, 0];
+            assert!(matches!(dec(&wire), Err(FrameError::Protocol(_))), "rsv {rsv:#x}");
+        }
+    }
+
+    #[test]
+    fn reserved_opcodes_rejected() {
+        for op in [0x3, 0x4, 0x5, 0x6, 0x7, 0xB, 0xC, 0xD, 0xE, 0xF] {
+            let wire = [0x80 | op, 0x80, 0, 0, 0, 0];
+            assert!(matches!(dec(&wire), Err(FrameError::Protocol(_))), "op {op:#x}");
+        }
+    }
+
+    #[test]
+    fn fragmented_control_rejected() {
+        let wire = [0x09, 0x80, 0, 0, 0, 0]; // ping, FIN=0
+        assert_eq!(dec(&wire), Err(FrameError::Protocol("fragmented control frame")));
+    }
+
+    #[test]
+    fn oversize_control_rejected() {
+        let wire = [0x89, 0x80 | 126, 0x00, 0x7E]; // ping, 16-bit len 126
+        assert_eq!(dec(&wire), Err(FrameError::Protocol("control payload > 125")));
+    }
+
+    #[test]
+    fn non_minimal_lengths_rejected() {
+        // 16-bit form carrying 5.
+        let w16 = [0x81, 0x80 | 126, 0x00, 0x05];
+        assert_eq!(dec(&w16), Err(FrameError::Protocol("non-minimal 16-bit length")));
+        // 64-bit form carrying 5.
+        let w64 = [0x81, 0x80 | 127, 0, 0, 0, 0, 0, 0, 0, 0x05];
+        assert_eq!(dec(&w64), Err(FrameError::Protocol("non-minimal 64-bit length")));
+    }
+
+    #[test]
+    fn msb_set_64bit_length_rejected() {
+        let wire = [0x81, 0x80 | 127, 0x80, 0, 0, 0, 0, 0, 0, 0];
+        assert_eq!(dec(&wire), Err(FrameError::Protocol("64-bit length MSB set")));
+    }
+
+    #[test]
+    fn oversize_fails_before_payload_arrives() {
+        // Header promises 1 MiB + 1 with a 1 MiB cap: must fail with just
+        // the header in hand, not Ok(None).
+        let mut wire = vec![0x82, 0x80 | 127];
+        wire.extend_from_slice(&((MAX as u64) + 1).to_be_bytes());
+        assert_eq!(dec(&wire), Err(FrameError::TooLarge));
+    }
+
+    // ----- close payloads. -----
+
+    #[test]
+    fn close_payload_parsing() {
+        assert_eq!(parse_close_payload(&[]), Ok(None));
+        assert_eq!(
+            parse_close_payload(&[0x03]),
+            Err(FrameError::Protocol("1-byte close payload"))
+        );
+        let normal = close_payload(1000, "bye");
+        assert_eq!(parse_close_payload(&normal), Ok(Some((1000, "bye".into()))));
+        // Signalling-only and reserved codes are invalid on the wire.
+        for bad in [999u16, 1004, 1005, 1006, 1015, 1100, 2999, 5000] {
+            assert!(
+                parse_close_payload(&bad.to_be_bytes()).is_err(),
+                "code {bad}"
+            );
+        }
+        for good in [1000u16, 1001, 1002, 1003, 1007, 1011, 3000, 4999] {
+            assert!(
+                parse_close_payload(&good.to_be_bytes()).is_ok(),
+                "code {good}"
+            );
+        }
+    }
+
+    #[test]
+    fn close_payload_reason_truncates_on_char_boundary() {
+        let reason = "é".repeat(100); // 200 bytes of 2-byte chars
+        let p = close_payload(1000, &reason);
+        assert!(p.len() <= 125);
+        assert_eq!(p.len() % 2, 0, "must not split the 2-byte char");
+        assert!(std::str::from_utf8(&p[2..]).is_ok());
+    }
+
+    // ----- assembler. -----
+
+    #[test]
+    fn assembler_rejects_orphan_continuation() {
+        let mut a = Assembler::new(MAX);
+        let f = Frame { fin: true, opcode: Opcode::Continuation, payload: vec![] };
+        assert_eq!(
+            a.push(f),
+            Err(FrameError::Protocol("continuation without a message"))
+        );
+    }
+
+    #[test]
+    fn assembler_rejects_interleaved_data_message() {
+        let mut a = Assembler::new(MAX);
+        let start = Frame { fin: false, opcode: Opcode::Text, payload: b"a".to_vec() };
+        a.push(start).unwrap();
+        let intruder = Frame::new(Opcode::Binary, b"b".to_vec());
+        assert_eq!(
+            a.push(intruder),
+            Err(FrameError::Protocol("new data frame mid-fragmentation"))
+        );
+    }
+
+    #[test]
+    fn assembler_message_size_cap_spans_fragments() {
+        let mut a = Assembler::new(10);
+        let f1 = Frame { fin: false, opcode: Opcode::Binary, payload: vec![0; 6] };
+        let f2 = Frame { fin: true, opcode: Opcode::Continuation, payload: vec![0; 6] };
+        assert_eq!(a.push(f1).unwrap(), None);
+        assert_eq!(a.push(f2), Err(FrameError::TooLarge));
+        // And the unfragmented fast path is capped too.
+        assert_eq!(
+            a.push(Frame::new(Opcode::Binary, vec![0; 11])),
+            Err(FrameError::TooLarge)
+        );
+    }
+
+    #[test]
+    fn assembler_text_utf8_validated_on_completion() {
+        let mut a = Assembler::new(MAX);
+        // A 2-byte UTF-8 char split across the fragment boundary must
+        // still assemble — validation is whole-message.
+        let bytes = "héllo".as_bytes();
+        let f1 = Frame { fin: false, opcode: Opcode::Text, payload: bytes[..2].to_vec() };
+        let f2 = Frame { fin: true, opcode: Opcode::Continuation, payload: bytes[2..].to_vec() };
+        assert_eq!(a.push(f1).unwrap(), None);
+        assert_eq!(a.push(f2).unwrap(), Some(Message::Text("héllo".into())));
+
+        // Invalid UTF-8 → BadUtf8 (close 1007).
+        let bad = Frame::new(Opcode::Text, vec![0xFF, 0xFE]);
+        assert_eq!(a.push(bad), Err(FrameError::BadUtf8));
+        assert_eq!(FrameError::BadUtf8.close_code(), 1007);
+    }
+
+    #[test]
+    fn assembler_reusable_after_message() {
+        let mut a = Assembler::new(MAX);
+        for _ in 0..3 {
+            let f1 = Frame { fin: false, opcode: Opcode::Text, payload: b"He".to_vec() };
+            let f2 = Frame { fin: true, opcode: Opcode::Continuation, payload: b"llo".to_vec() };
+            assert_eq!(a.push(f1).unwrap(), None);
+            assert_eq!(a.push(f2).unwrap(), Some(Message::Text("Hello".into())));
+        }
+    }
+}

src/ws/handshake.rs

@@ -0,0 +1,250 @@
+//! RFC 6455 §4.2 — the opening handshake, server side.
+//!
+//! Pure functions over an already-parsed request; no io. The connection
+//! actor owns the wire.
+
+use crate::conn::{Conn, HttpVersion, Method};
+
+/// RFC 6455 §1.3 — the fixed GUID appended to the client key.
+const WS_GUID: &str = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
+
+/// Why a handshake was rejected. Maps onto a response via
+/// [`Rejection::status`]: everything is a `400` except a version
+/// mismatch, which RFC 6455 §4.2.2 answers with `426` + a
+/// `sec-websocket-version: 13` header so the client can retry.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Rejection {
+    /// Handshake requests must be GET (§4.2.1).
+    NotGet,
+    /// HTTP/1.1 or higher required (§4.2.1).
+    BadHttpVersion,
+    /// `Host` header missing (§4.2.1 item 2).
+    MissingHost,
+    /// `Upgrade` header missing or lacks the `websocket` token.
+    NotAnUpgrade,
+    /// `Connection` header missing or lacks the `upgrade` token.
+    ConnectionNotUpgrade,
+    /// `Sec-WebSocket-Key` missing or not base64 of exactly 16 bytes.
+    BadKey,
+    /// `Sec-WebSocket-Version` is not 13 → 426 Upgrade Required.
+    UnsupportedVersion,
+}
+
+impl Rejection {
+    pub fn status(self) -> u16 {
+        match self {
+            Rejection::UnsupportedVersion => 426,
+            _ => 400,
+        }
+    }
+}
+
+/// Cheap routing predicate: does this request *ask* for a WebSocket
+/// upgrade? (Token checks only — full validation happens in
+/// [`validate`].) Lets a handler branch without committing to the
+/// handshake.
+pub fn is_upgrade_request(conn: &Conn) -> bool {
+    has_token(conn.headers.get("upgrade"), "websocket")
+        && has_token(conn.headers.get("connection"), "upgrade")
+}
+
+/// Full §4.2.1 server-side validation. `Ok` carries the computed
+/// `Sec-WebSocket-Accept` value.
+pub fn validate(conn: &Conn) -> Result<String, Rejection> {
+    if conn.method != Method::Get {
+        return Err(Rejection::NotGet);
+    }
+    if conn.version != HttpVersion::Http11 {
+        return Err(Rejection::BadHttpVersion);
+    }
+    if conn.headers.get("host").is_none() {
+        return Err(Rejection::MissingHost);
+    }
+    if !has_token(conn.headers.get("upgrade"), "websocket") {
+        return Err(Rejection::NotAnUpgrade);
+    }
+    if !has_token(conn.headers.get("connection"), "upgrade") {
+        return Err(Rejection::ConnectionNotUpgrade);
+    }
+    match conn.headers.get("sec-websocket-version") {
+        Some(v) if v.trim() == "13" => {}
+        _ => return Err(Rejection::UnsupportedVersion),
+    }
+    let key = conn
+        .headers
+        .get("sec-websocket-key")
+        .map(str::trim)
+        .ok_or(Rejection::BadKey)?;
+    if !key_is_b64_16_bytes(key) {
+        return Err(Rejection::BadKey);
+    }
+    Ok(accept_key(key))
+}
+
+/// `base64(SHA1(key ++ GUID))` — §4.2.2 item 5.4.
+pub fn accept_key(key: &str) -> String {
+    let mut h = sha1_smol::Sha1::new();
+    h.update(key.as_bytes());
+    h.update(WS_GUID.as_bytes());
+    b64(&h.digest().bytes())
+}
+
+/// Case-insensitive token search in a comma-separated header value.
+/// `Connection: keep-alive, Upgrade` must match token `upgrade`.
+fn has_token(value: Option<&str>, token: &str) -> bool {
+    match value {
+        None => false,
+        Some(v) => v
+            .split(',')
+            .any(|t| t.trim().eq_ignore_ascii_case(token)),
+    }
+}
+
+/// The client key must be base64 of exactly 16 bytes: 24 chars, last two
+/// `==`, the rest in the standard alphabet (RFC 4648 §4). We never
+/// decode it — §4.2.2 only concatenates the encoded form.
+fn key_is_b64_16_bytes(key: &str) -> bool {
+    let b = key.as_bytes();
+    b.len() == 24
+        && b[22] == b'='
+        && b[23] == b'='
+        && b[..22]
+            .iter()
+            .all(|&c| c.is_ascii_alphanumeric() || c == b'+' || c == b'/')
+}
+
+/// RFC 4648 base64 *encoding* (standard alphabet, padded). Encode-only
+/// and not cryptographic — kept in-tree by design; do not grow a decoder
+/// here without a design conversation (decoding is where the parsing
+/// bugs live).
+pub(crate) fn b64(input: &[u8]) -> String {
+    const ALPHA: &[u8; 64] =
+        b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+    let mut out = String::with_capacity(input.len().div_ceil(3) * 4);
+    for chunk in input.chunks(3) {
+        let b0 = chunk[0] as u32;
+        let b1 = *chunk.get(1).unwrap_or(&0) as u32;
+        let b2 = *chunk.get(2).unwrap_or(&0) as u32;
+        let n = (b0 << 16) | (b1 << 8) | b2;
+        out.push(ALPHA[(n >> 18) as usize & 63] as char);
+        out.push(ALPHA[(n >> 12) as usize & 63] as char);
+        out.push(if chunk.len() > 1 { ALPHA[(n >> 6) as usize & 63] as char } else { '=' });
+        out.push(if chunk.len() > 2 { ALPHA[n as usize & 63] as char } else { '=' });
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::conn::HeaderMap;
+
+    // ----- base64: RFC 4648 §10 test vectors. -----
+    #[test]
+    fn b64_rfc4648_vectors() {
+        assert_eq!(b64(b""), "");
+        assert_eq!(b64(b"f"), "Zg==");
+        assert_eq!(b64(b"fo"), "Zm8=");
+        assert_eq!(b64(b"foo"), "Zm9v");
+        assert_eq!(b64(b"foob"), "Zm9vYg==");
+        assert_eq!(b64(b"fooba"), "Zm9vYmE=");
+        assert_eq!(b64(b"foobar"), "Zm9vYmFy");
+    }
+
+    // ----- accept key: the RFC 6455 §1.3 worked example. -----
+    #[test]
+    fn accept_key_rfc6455_example() {
+        assert_eq!(
+            accept_key("dGhlIHNhbXBsZSBub25jZQ=="),
+            "s3pPLMBiTxaQ9kYGzzhZRbK+xOo="
+        );
+    }
+
+    fn ws_conn() -> Conn {
+        let mut c = Conn::new();
+        c.method = Method::Get;
+        c.version = HttpVersion::Http11;
+        let mut h = HeaderMap::new();
+        h.append("host", "example.com");
+        h.append("upgrade", "websocket");
+        h.append("connection", "Upgrade");
+        h.append("sec-websocket-key", "dGhlIHNhbXBsZSBub25jZQ==");
+        h.append("sec-websocket-version", "13");
+        c.headers = h;
+        c
+    }
+
+    #[test]
+    fn validate_happy_path() {
+        assert_eq!(
+            validate(&ws_conn()).unwrap(),
+            "s3pPLMBiTxaQ9kYGzzhZRbK+xOo="
+        );
+    }
+
+    #[test]
+    fn validate_rejects_post() {
+        let mut c = ws_conn();
+        c.method = Method::Post;
+        assert_eq!(validate(&c), Err(Rejection::NotGet));
+    }
+
+    #[test]
+    fn validate_rejects_http10() {
+        let mut c = ws_conn();
+        c.version = HttpVersion::Http10;
+        assert_eq!(validate(&c), Err(Rejection::BadHttpVersion));
+    }
+
+    #[test]
+    fn validate_requires_host() {
+        let mut c = ws_conn();
+        let mut h = HeaderMap::new();
+        for (n, v) in c.headers.iter() {
+            if n != "host" {
+                h.append(n, v);
+            }
+        }
+        c.headers = h;
+        assert_eq!(validate(&c), Err(Rejection::MissingHost));
+    }
+
+    #[test]
+    fn validate_connection_token_in_list() {
+        let mut c = ws_conn();
+        c.headers.set("connection", "keep-alive, Upgrade");
+        assert!(validate(&c).is_ok());
+    }
+
+    #[test]
+    fn validate_rejects_wrong_ws_version() {
+        let mut c = ws_conn();
+        c.headers.set("sec-websocket-version", "8");
+        assert_eq!(validate(&c), Err(Rejection::UnsupportedVersion));
+        assert_eq!(Rejection::UnsupportedVersion.status(), 426);
+    }
+
+    #[test]
+    fn validate_rejects_bad_keys() {
+        for bad in [
+            "tooshort==",
+            "dGhlIHNhbXBsZSBub25jZQ=!",          // bad padding char
+            "dGhlIHNhbXBsZSBub25jZSE=",          // single pad = 17 bytes, not 16
+            "dGhlIHNhbXBsZSBub25jZQQQ",          // unpadded 24 chars (18 bytes)
+            "",
+        ] {
+            let mut c = ws_conn();
+            c.headers.set("sec-websocket-key", bad);
+            assert_eq!(validate(&c), Err(Rejection::BadKey), "key: {bad:?}");
+        }
+    }
+
+    #[test]
+    fn is_upgrade_request_predicate() {
+        assert!(is_upgrade_request(&ws_conn()));
+        let mut c = ws_conn();
+        c.headers.set("upgrade", "h2c");
+        assert!(!is_upgrade_request(&c));
+        assert!(!is_upgrade_request(&Conn::new()));
+    }
+}

src/ws/mod.rs

@@ -0,0 +1,35 @@
+//! WebSocket support (RFC 6455).
+//!
+//! v0.4 chunk 1: the upgrade handshake. A handler that wants to speak
+//! WebSocket calls [`Conn::upgrade`](crate::Conn::upgrade); on a valid
+//! handshake the connection actor writes the `101 Switching Protocols`
+//! response and leaves the HTTP request loop. (Until the duplex wiring
+//! lands — chunk 3 — leaving the loop closes the socket; the 101 itself
+//! is correct and tested.)
+//!
+//! Dependency note: SHA-1 comes from `sha1_smol` (zero transitive deps),
+//! spending urus dependency slot #3 — agreed in the v0.4 design pass over
+//! vendoring. Base64 here is the 20-byte *encode* direction only and is
+//! not cryptographic, so that stays in-tree (`handshake::b64`).
+
+pub mod duplex;
+pub mod frame;
+pub mod handshake;
+
+pub use duplex::{WsClosed, WsHandler, WsSender};
+pub use frame::{Frame, FrameError, Message, Opcode};
+pub use handshake::Rejection;
+
+/// Payload carried on a [`Conn`](crate::Conn) whose handler accepted a
+/// WebSocket upgrade: the boxed [`WsHandler`] the duplex loop will drive
+/// (the chunk-3 growth this was reserved for). Still opaque outside the
+/// crate.
+pub struct WsUpgrade {
+    pub(crate) handler: Box<dyn WsHandler>,
+}
+
+impl std::fmt::Debug for WsUpgrade {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.write_str("WsUpgrade { handler: .. }")
+    }
+}