Refactor fanout to per-connection tasks with debouncing and reconnection grace

- Add RenderTrigger enum to connection.rs (avoids circular imports)
- Replace ConnectionState.sse_sender with trigger_tx + pipe_tx channels
- Add get_trigger_sender and get_pipe_sender to ConnectionManager
- Extract render_and_send helper to eliminate duplicated render/SSE logic
- Implement connection_task: long-lived per-connection coroutine that owns
  the SSE pipe, debounces render triggers (2ms), and survives disconnects for
  a 30s grace period to allow clean reconnection
- Update sse_handler: spawns connection_task on fresh connect, hands new SSE
  pipe to existing task on reconnect; removes cleanup-on-disconnect spawn
- Update spawn_fanout: now a pure router — sends RenderTrigger::Invalidated
  to each subscribed connection's task; no render logic remains in fanout
- Bump broadcast channel capacity from 256 to 16384 in Store::new
- Merge brotli compression branch (config hot-reload, BrotliBody middleware)

https://claude.ai/code/session_01QiTaFtwXETxJDk79XcgfrN

src/connection.rs

@@ -6,23 +6,26 @@ use std::sync::Arc;
 use tokio::sync::mpsc;
 use uuid::Uuid;
 
+// ---------------------------------------------------------------------------
+// RenderTrigger
+// ---------------------------------------------------------------------------
+
+/// Signal sent to a connection task to request a rerender.
+pub enum RenderTrigger {
+    Invalidated,
+}
+
 // ---------------------------------------------------------------------------
 // Connection state
 // ---------------------------------------------------------------------------
 
 /// Per-connection state stored in the manager.
 pub struct ConnectionState {
-    /// Sender half of the per-connection SSE channel.
-    ///
-    /// The fanout task sends fully-constructed axum `Event`s here; the SSE
-    /// handler streams them directly to the client without re-wrapping.
-    pub sse_sender: mpsc::Sender<Event>,
-
-    /// The full signal JSON from the most recent render for this connection.
-    ///
-    /// Stored so the fanout task can reconstruct a `SignalStore` and build a
-    /// `RenderContext` for server-initiated rerenders, without a client
-    /// request carrying the signals.
+    /// Sends render triggers to the connection task.
+    pub trigger_tx: mpsc::Sender<RenderTrigger>,
+    /// Sends new SSE pipe senders to the connection task on reconnect.
+    pub pipe_tx: mpsc::Sender<mpsc::Sender<Event>>,
+    /// Last known signals JSON, updated by action handlers.
     pub last_signals_json: Option<String>,
 }
 
@@ -35,8 +38,8 @@ pub struct ConnectionState {
 /// Accessed from:
 /// - `GET /sse` handler (insert)
 /// - `POST /action` handler (update signals)
-/// - SSE drop cleanup (remove)
-/// - Fanout task (read sender + signals for rerender)
+/// - Fanout task (get trigger sender for rerender)
+/// - Connection task (cleanup on grace period expiry)
 pub struct ConnectionManager {
     connections: DashMap<Uuid, ConnectionState>,
 }
@@ -48,26 +51,29 @@ impl ConnectionManager {
         }
     }
 
-    /// Register a new connection with its SSE sender.
-    pub fn insert(&self, id: Uuid, sender: mpsc::Sender<Event>) {
+    /// Register a new connection with its trigger and pipe senders.
+    pub fn insert(&self, id: Uuid, trigger_tx: mpsc::Sender<RenderTrigger>, pipe_tx: mpsc::Sender<mpsc::Sender<Event>>) {
         self.connections.insert(
             id,
             ConnectionState {
-                sse_sender: sender,
+                trigger_tx,
+                pipe_tx,
                 last_signals_json: None,
             },
         );
     }
 
-    /// Get the SSE sender for a connection.
-    pub fn get_sender(&self, id: &Uuid) -> Option<mpsc::Sender<Event>> {
-        self.connections.get(id).map(|c| c.sse_sender.clone())
+    /// Get the render trigger sender for a connection.
+    pub fn get_trigger_sender(&self, id: &Uuid) -> Option<mpsc::Sender<RenderTrigger>> {
+        self.connections.get(id).map(|c| c.trigger_tx.clone())
+    }
+
+    /// Get the pipe sender for a connection (used to hand off a new SSE pipe on reconnect).
+    pub fn get_pipe_sender(&self, id: &Uuid) -> Option<mpsc::Sender<mpsc::Sender<Event>>> {
+        self.connections.get(id).map(|c| c.pipe_tx.clone())
     }
 
     /// Get the last signals JSON for a connection.
-    ///
-    /// Called by the fanout task to reconstruct signal state for a
-    /// server-initiated rerender.
     pub fn get_signals(&self, id: &Uuid) -> Option<String> {
         self.connections
             .get(id)
@@ -75,15 +81,13 @@ impl ConnectionManager {
     }
 
     /// Update the stored signals for a connection.
-    ///
-    /// Called by `POST /action` after ingesting the client's signal blob.
     pub fn update_signals(&self, id: &Uuid, signals_json: String) {
         if let Some(mut conn) = self.connections.get_mut(id) {
             conn.last_signals_json = Some(signals_json);
         }
     }
 
-    /// Remove a connection (called on SSE pipe drop).
+    /// Remove a connection.
     pub fn remove(&self, id: &Uuid) -> Option<(Uuid, ConnectionState)> {
         self.connections.remove(id)
     }
@@ -168,4 +172,4 @@ impl SubscriptionRegistry {
             .map(|c| c.clone())
             .unwrap_or_default()
     }
-}
+}

src/lib.rs

@@ -30,7 +30,7 @@ pub use store::{Store, KVStore};
 #[cfg(feature = "pg_replication")]
 pub use pg_query::PgQuery;
 pub use context::{RenderContext, ComponentTree, ComponentNode};
-pub use connection::{ConnectionManager, ConnectionState, SubscriptionRegistry};
+pub use connection::{ConnectionManager, ConnectionState, SubscriptionRegistry, RenderTrigger};
 pub use sse::{format_patch_elements, format_patch_signals};
 pub use server::{AppState, SharedState, RenderFn, sse_handler, spawn_fanout, ingest_signals, ActionParams, SseParams};
 pub use config::{LiveVueConfig, ServerConfig, BrotliConfig, SharedConfig, load_config, load_and_watch_config};

src/server.rs

@@ -1,5 +1,5 @@
 use crate::config::{LiveVueConfig, SharedConfig};
-use crate::connection::{ConnectionManager, SubscriptionRegistry};
+use crate::connection::{ConnectionManager, RenderTrigger, SubscriptionRegistry};
 use crate::context::{ComponentTree, RenderContext};
 use crate::query::CacheKey;
 use crate::signal::SignalStore;
@@ -12,9 +12,13 @@ use std::convert::Infallible;
 use std::sync::Arc;
 use tokio::sync::mpsc;
 use tokio::sync::RwLock;
+use tokio::time::{sleep, Duration};
 use tokio_stream::wrappers::ReceiverStream;
 use uuid::Uuid;
 
+const DEBOUNCE_MS: u64 = 2;
+const RECONNECT_GRACE_SECS: u64 = 30;
+
 // ---------------------------------------------------------------------------
 // RenderFn
 // ---------------------------------------------------------------------------
@@ -99,6 +103,151 @@ impl AppState {
     }
 }
 
+// ---------------------------------------------------------------------------
+// render_and_send helper
+// ---------------------------------------------------------------------------
+
+/// Parse signals, render, and send SSE events for one connection.
+///
+/// On any error, logs and returns without panicking.
+async fn render_and_send(
+    conn_id: Uuid,
+    signals_json: &str,
+    sse_tx: &mpsc::Sender<Event>,
+    state: &AppState,
+) {
+    let signals = match serde_json::from_str::<serde_json::Value>(signals_json) {
+        Ok(v) => SignalStore::from_json(v),
+        Err(e) => {
+            tracing::error!("render_and_send: failed to parse signals for {}: {}", conn_id, e);
+            return;
+        }
+    };
+
+    let tree: ComponentTree = signals
+        .get("tree")
+        .and_then(|v| serde_json::from_value(v.clone()).ok())
+        .unwrap_or_default();
+
+    let cx = RenderContext::new(conn_id, signals, tree, state.store.clone());
+    match (state.render_fn)(cx).await {
+        Ok((html, keys)) => {
+            state.subscriptions.update(conn_id, keys);
+
+            let data_payload: String = html
+                .lines()
+                .map(|line| format!("elements {}", line))
+                .collect::<Vec<_>>()
+                .join("\n");
+
+            let html_event = Event::default()
+                .event("datastar-patch-elements")
+                .data(data_payload);
+
+            if sse_tx.send(html_event).await.is_err() {
+                tracing::debug!("render_and_send: SSE channel closed for {}", conn_id);
+                return;
+            }
+
+            let signals_event = Event::default()
+                .event("datastar-patch-signals")
+                .data("signals ".to_owned() + signals_json);
+
+            if sse_tx.send(signals_event).await.is_err() {
+                tracing::debug!("render_and_send: SSE channel closed for {}", conn_id);
+            }
+        }
+        Err(e) => {
+            tracing::error!("render_and_send: render error for {}: {}", conn_id, e);
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// connection_task
+// ---------------------------------------------------------------------------
+
+/// Long-lived task that owns the SSE pipe for one logical connection.
+///
+/// Survives SSE disconnects for a grace period (RECONNECT_GRACE_SECS), allowing
+/// the client to reconnect cleanly. Debounces render triggers by DEBOUNCE_MS.
+async fn connection_task(
+    conn_id: Uuid,
+    mut inbox: mpsc::Receiver<RenderTrigger>,
+    mut pipe_rx: mpsc::Receiver<mpsc::Sender<Event>>,
+    initial_signals_json: String,
+    state: SharedState,
+) {
+    let mut signals_json = initial_signals_json;
+
+    loop {
+        // ----------------------------------------------------------------
+        // Wait for first/next SSE pipe (with reconnect grace period).
+        // ----------------------------------------------------------------
+        let sse_tx: mpsc::Sender<Event> = tokio::select! {
+            maybe_pipe = pipe_rx.recv() => {
+                match maybe_pipe {
+                    Some(tx) => tx,
+                    None => {
+                        // pipe channel closed — shut down
+                        return;
+                    }
+                }
+            }
+            _ = sleep(Duration::from_secs(RECONNECT_GRACE_SECS)) => {
+                tracing::debug!(
+                    "connection_task: grace period expired for {}, cleaning up",
+                    conn_id
+                );
+                state.connections.remove(&conn_id);
+                state.subscriptions.remove_connection(&conn_id);
+                return;
+            }
+        };
+
+        // Do an immediate render on pipe arrival.
+        render_and_send(conn_id, &signals_json, &sse_tx, &state).await;
+
+        // ----------------------------------------------------------------
+        // Main event loop for this pipe.
+        // ----------------------------------------------------------------
+        loop {
+            tokio::select! {
+                // SSE pipe dropped by the HTTP layer — wait for reconnect.
+                _ = sse_tx.closed() => {
+                    tracing::debug!("connection_task: SSE pipe closed for {}, waiting for reconnect", conn_id);
+                    break; // back to outer loop to wait for new pipe
+                }
+
+                // Trigger channel closed — task is being shut down.
+                maybe_trigger = inbox.recv() => {
+                    match maybe_trigger {
+                        None => {
+                            // Trigger sender dropped — clean up and exit.
+                            state.connections.remove(&conn_id);
+                            state.subscriptions.remove_connection(&conn_id);
+                            return;
+                        }
+                        Some(_) => {
+                            // Debounce: drain any additional triggers within DEBOUNCE_MS.
+                            sleep(Duration::from_millis(DEBOUNCE_MS)).await;
+                            while inbox.try_recv().is_ok() {}
+
+                            // Read fresh signals and render.
+                            signals_json = state
+                                .connections
+                                .get_signals(&conn_id)
+                                .unwrap_or_else(|| signals_json.clone());
+
+                            render_and_send(conn_id, &signals_json, &sse_tx, &state).await;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
 // ---------------------------------------------------------------------------
 // Fanout task
 // ---------------------------------------------------------------------------
@@ -108,16 +257,11 @@ impl AppState {
 /// Must be called once at startup, after building `AppState`. The task owns
 /// a `broadcast::Receiver<CacheKey>` and runs for the lifetime of the server.
 ///
-/// On each invalidation event:
-/// 1. Look up subscribed connections via `SubscriptionRegistry`.
-/// 2. For each connection, fetch `last_signals_json` + SSE sender.
-/// 3. Reconstruct `SignalStore` + `ComponentTree`, build `RenderContext`.
-/// 4. Call `render_fn` to produce HTML.
-/// 5. Frame as SSE and send down the connection's SSE channel.
-/// 6. Update subscription keys and `last_signals_json` from the new render.
+/// On each invalidation event, routes a `RenderTrigger::Invalidated` to each
+/// subscribed connection's long-lived connection task.
 ///
 /// ```ignore
-/// let state = AppState::new(store.clone(), render_fn);
+/// let state = AppState::new(store.clone(), render_fn, config);
 /// spawn_fanout(state.clone());
 /// ```
 pub fn spawn_fanout(state: SharedState) {
@@ -140,69 +284,9 @@ pub fn spawn_fanout(state: SharedState) {
             let conn_ids = state.subscriptions.get_connections_for_key(&key);
 
             for conn_id in conn_ids {
-                let signals_json = state
-                    .connections
-                    .get_signals(&conn_id)
-                    .unwrap_or_else(|| "{}".to_string());
-                let Some(sse_tx) = state.connections.get_sender(&conn_id) else {
-                    continue;
-                };
-
-                let signals = match serde_json::from_str::<serde_json::Value>(&signals_json) {
-                    Ok(v) => SignalStore::from_json(v),
-                    Err(e) => {
-                        tracing::error!("fanout: failed to parse signals for {}: {}", conn_id, e);
-                        continue;
-                    }
-                };
-
-                // Parse the component tree from the `tree` signal.
-                let tree = signals
-                    .get("tree")
-                    .and_then(|v| serde_json::from_value(v.clone()).ok())
-                    .unwrap_or_default();
-
-                let mut cx = RenderContext::new(conn_id, signals, tree, state.store.clone());
-
-                let render_fn = state.render_fn.clone();
-                let state_ref = state.clone();
-
-                tokio::spawn(async move {
-                    match render_fn(cx).await {
-                        Ok((html, keys)) => {
-                            state_ref.subscriptions.update(conn_id, keys);
-
-                            // Build a datastar-patch-elements SSE event.
-                            // Each HTML line gets an `elements ` prefix; axum's
-                            // Event::data() splits on \n and writes a `data:`
-                            // line for each, which is correct SSE multiline format.
-                            let data_payload: String = html
-                                .lines()
-                                .map(|line| format!("elements {}", line))
-                                .collect::<Vec<_>>()
-                                .join("\n");
-
-                            let html_event = Event::default()
-                                .event("datastar-patch-elements")
-                                .data(data_payload);
-
-                            if sse_tx.send(html_event).await.is_err() {
-                                tracing::debug!("fanout: SSE channel closed for {}", conn_id);
-                            }
-
-                            let signals_event = Event::default()
-                                .event("datastar-patch-signals")
-                                .data("signals ".to_owned() + &signals_json);
-
-                            if sse_tx.send(signals_event).await.is_err() {
-                                tracing::debug!("fanout: SSE channel closed for {}", conn_id);
-                            }
-                        }
-                        Err(e) => {
-                            tracing::error!("fanout: render error for {}: {}", conn_id, e);
-                        }
-                    }
-                });
+                if let Some(tx) = state.connections.get_trigger_sender(&conn_id) {
+                    tx.send(RenderTrigger::Invalidated).await.ok();
+                }
             }
         }
     });
@@ -220,73 +304,44 @@ pub struct SseParams {
 
 /// `GET /sse?conn=<uuid>` — Long-lived SSE pipe for server-initiated push.
 ///
-/// The conn_id is generated by `GET /` and pre-seeded with initial signals
-/// in `ConnectionManager` before this handler is called. On connect, the
-/// handler immediately triggers a render and pushes the result down the pipe,
-/// so the client sees content without any further round-trip.
+/// On first connect, spawns a `connection_task` that owns the lifecycle of the
+/// connection. On reconnect with the same conn_id, hands a new SSE pipe to the
+/// already-running task. The task survives disconnects for RECONNECT_GRACE_SECS.
 pub async fn sse_handler(
     State(state): State<SharedState>,
     AxumQuery(params): AxumQuery<SseParams>,
 ) -> Sse<impl tokio_stream::Stream<Item = Result<Event, Infallible>>> {
     let conn_id = params.conn;
-    let (tx, rx) = mpsc::channel::<Event>(32);
-    let tx_watch = tx.clone();
 
-    state.connections.insert(conn_id, tx.clone());
+    let pipe_tx: mpsc::Sender<mpsc::Sender<Event>> = if !state.connections.contains(&conn_id) {
+        // Fresh connection — create channels and spawn the connection task.
+        let (trigger_tx, trigger_rx) = mpsc::channel::<RenderTrigger>(32);
+        let (pipe_tx, pipe_rx) = mpsc::channel::<mpsc::Sender<Event>>(4);
 
-    // Cleanup on disconnect
-    let state_cleanup = state.clone();
-    tokio::spawn(async move {
-        tx_watch.closed().await;
-        state_cleanup.connections.remove(&conn_id);
-        state_cleanup.subscriptions.remove_connection(&conn_id);
-        tracing::debug!("cleaned up connection {}", conn_id);
-    });
-    println!("SSE Handler called");
+        let initial_signals = state
+            .connections
+            .get_signals(&conn_id)
+            .unwrap_or_else(|| "{}".to_string());
 
-    // Trigger first render immediately using the pre-seeded signals.
-    let signals_json = state
-        .connections
-        .get_signals(&conn_id)
-        .unwrap_or_else(|| "{}".to_string());
+        state.connections.insert(conn_id, trigger_tx, pipe_tx.clone());
 
-    let render_fn = state.render_fn.clone();
-    let store = state.store.clone();
-    let subscriptions = state.subscriptions.clone();
-    let tx_init = tx.clone();
+        let state_task = state.clone();
+        tokio::spawn(async move {
+            connection_task(conn_id, trigger_rx, pipe_rx, initial_signals, state_task).await;
+        });
 
-    tokio::spawn(async move {
-        let signals = match serde_json::from_str::<serde_json::Value>(&signals_json) {
-            Ok(v) => SignalStore::from_json(v),
-            Err(e) => {
-                tracing::error!("sse_handler: failed to parse seeded signals: {}", e);
-                return;
-            }
-        };
-        let tree = signals
-            .get("tree")
-            .and_then(|v| serde_json::from_value(v.clone()).ok())
-            .unwrap_or_default();
+        pipe_tx
+    } else {
+        // Reconnect — retrieve existing pipe sender.
+        state.connections.get_pipe_sender(&conn_id)
+            .expect("connection exists but has no pipe_tx")
+    };
 
-        let cx = RenderContext::new(conn_id, signals, tree, store);
-        match render_fn(cx).await {
-            Ok((html, keys)) => {
-                subscriptions.update(conn_id, keys);
-                let data_payload = html
-                    .lines()
-                    .map(|line| format!("elements {}", line))
-                    .collect::<Vec<_>>()
-                    .join("\n");
-                let event = Event::default()
-                    .event("datastar-patch-elements")
-                    .data(data_payload);
-                tx_init.send(event).await.ok();
-            }
-            Err(e) => tracing::error!("sse_handler: initial render failed: {}", e),
-        }
-    });
+    // Create a fresh SSE channel for this HTTP connection's lifetime.
+    let (sse_tx, sse_rx) = mpsc::channel::<Event>(32);
+    pipe_tx.send(sse_tx).await.ok();
 
-    let stream = ReceiverStream::new(rx);
+    let stream = ReceiverStream::new(sse_rx);
     let event_stream = tokio_stream::StreamExt::map(stream, |event| Ok::<Event, Infallible>(event));
 
     Sse::new(event_stream).keep_alive(KeepAlive::default())

src/store.rs

@@ -108,7 +108,7 @@ impl Store {
     /// that can be buffered before slow receivers start lagging. The fanout
     /// task should be fast enough that this is never hit in practice.
     pub fn new(db: sqlx::SqlitePool) -> Arc<Self> {
-        let (events_tx, _) = broadcast::channel(256);
+        let (events_tx, _) = broadcast::channel(16384);
         let kv = Arc::new(KVStore::new(events_tx.clone()));
         Arc::new(Self {
             db,