diff --git a/README.md b/README.md
index 3b14de9..77b5c69 100644
--- a/README.md
+++ b/README.md
@@ -28,6 +28,7 @@ convenience wrapper around `runtime::init(Config::exact(1)).run(f)`.
 | `supervisor` | `Signal::Exit`/`Panic`/`Stopped` funnelled to a parent; `OneForOne`/`OneForAll`/`RestForOne` strategies + restart-intensity cap |
 | `monitor`    | `monitor(pid)` → one-shot `Receiver<Down>`; unidirectional death notice |
 | `link`       | bidirectional `link`/`unlink`; abnormal death propagates (cooperative stop, or an `ExitSignal` message under `trap_exit`) |
+| `gen_server` | `call` (sync request-reply) / `cast` (async) over one inbox; `ServerRef` + `init`/`terminate` hooks; server-down via channel closure |
 
 ## Quick taste
 
@@ -56,7 +57,7 @@ src/
   stack.rs context.rs preempt.rs pid.rs actor.rs
   scheduler.rs channel.rs mutex.rs timer.rs io.rs
   supervisor.rs monitor.rs link.rs runtime.rs
-  lib.rs
+  gen_server.rs lib.rs
 tests/
   per-module integration tests
 benches/
diff --git a/task.md b/task.md
index 2ddd2e3..77365be 100644
--- a/task.md
+++ b/task.md
@@ -166,6 +166,26 @@ Shipped. What landed vs the plan:
   `HashMap<String,Pid>` in `SharedState`.
 - gen_server-style call/cast: request-reply correlation as a thin layer over
   channels (`call` sends `{req, reply_tx}`, awaits `reply_rx`); no runtime change.
+  ✅ DONE (`a4fcf6c`). What landed vs the plan:
+  - `GenServer` trait on the state value: assoc `Call`/`Reply`/`Cast` types,
+    required `handle_call`/`handle_cast`, optional `init`/`terminate` hooks.
+    `ServerRef<G>` is a clonable inbox sender + `pid()`; `start` / `start_under`.
+  - One inbox, not two: a single `Envelope { Call(req, reply_tx) | Cast }`
+    channel, dispatched by variant. Forced by no-`select`/no-unified-mailbox —
+    a server can't wait on a call channel and a cast channel at once.
+  - Server-down falls out of channel closure (no monitor needed): `send` fails
+    if the inbox is gone; the reply sender drops on the server's unwind so a
+    parked caller wakes to `Err`. Both → `Call/CastError::ServerDown`.
+  - `terminate` runs via a drop guard → fires on *every* exit path (clean inbox
+    close, handler panic, `request_stop`), not just the clean one. Caveat: it
+    may run mid-unwind, so keep it non-blocking (a panic inside it during an
+    unwind double-panics → abort).
+  - No `handle_info`, no call timeout — both deferred to land with timeouts
+    (`handle_info` needs the still-unmade cross-channel mailbox merge; a call
+    timeout needs a per-`recv` deadline / `Signal::Timeout`).
+  - Pure additive layer (no Slot/scheduler/spawn/finalize change) → no perf
+    check run. Tests (`tests/gen_server.rs`): cast→call roundtrip, init/terminate
+    ordering, both server-down paths.
 - Docs lag: README still says "x86-64 Linux only — ARM64 … deferred" and the
   module table calls `context` x86-64-only; update for the aarch64 backend.