Add the Yaak Bridge so a browser tab can run the real engine

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

crates-server/yaak-server/src/events.rs

@@ -0,0 +1,117 @@
+//! The events channel: everything the browser tab would have received as a
+//! Tauri window event.
+//!
+//! Two directions ride the same WebSocket. Server to client is a broadcast, so
+//! `model_writes`, `stream_{id}` messages, toasts and plugin events all reach
+//! the tab through one pipe. Client to server exists because some plugin host
+//! requests are questions — a prompt round-trips through the UI and comes back
+//! keyed by the originating event's id, exactly as the desktop app's
+//! `call_frontend` does with window events.
+
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use std::sync::{Arc, Mutex};
+use tokio::sync::{broadcast, mpsc};
+
+/// One frame in either direction: a name and a JSON payload.
+///
+/// Deliberately the same shape both ways, and the same shape as the desktop's
+/// event payloads, so `platform.listen` on the browser side hands the payload
+/// to callers unwrapped.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct EventFrame {
+    pub event: String,
+    #[serde(default)]
+    pub payload: serde_json::Value,
+}
+
+#[derive(Clone)]
+pub struct EventHub {
+    outbound: broadcast::Sender<EventFrame>,
+    /// Listeners waiting on a named event from the client, keyed by event name.
+    inbound: Arc<Mutex<HashMap<String, Vec<mpsc::UnboundedSender<serde_json::Value>>>>>,
+}
+
+/// A subscription to one named client-sent event. Deregisters on drop, so a
+/// prompt that is never answered doesn't leak a listener for the process's life.
+pub struct InboundSubscription {
+    event: String,
+    rx: mpsc::UnboundedReceiver<serde_json::Value>,
+    inbound: Arc<Mutex<HashMap<String, Vec<mpsc::UnboundedSender<serde_json::Value>>>>>,
+}
+
+impl InboundSubscription {
+    pub async fn recv(&mut self) -> Option<serde_json::Value> {
+        self.rx.recv().await
+    }
+}
+
+impl Drop for InboundSubscription {
+    fn drop(&mut self) {
+        let mut inbound = match self.inbound.lock() {
+            Ok(inbound) => inbound,
+            Err(poisoned) => poisoned.into_inner(),
+        };
+        if let Some(senders) = inbound.get_mut(&self.event) {
+            senders.retain(|tx| !tx.is_closed());
+            if senders.is_empty() {
+                inbound.remove(&self.event);
+            }
+        }
+    }
+}
+
+impl EventHub {
+    pub fn new() -> Self {
+        // Bounded: a tab that stops reading gets dropped frames rather than
+        // growing the server's memory without limit. Model writes are the
+        // high-volume case (imports, bulk deletes) and they arrive in batches.
+        let (outbound, _) = broadcast::channel(1024);
+        Self { outbound, inbound: Arc::new(Mutex::new(HashMap::new())) }
+    }
+
+    /// Send an event to every connected tab. Fails silently when none is
+    /// connected, which is the normal state before a browser attaches.
+    pub fn emit<T: Serialize>(&self, event: impl Into<String>, payload: &T) {
+        let payload = match serde_json::to_value(payload) {
+            Ok(payload) => payload,
+            Err(e) => {
+                log::warn!("Failed to serialize event payload: {e}");
+                return;
+            }
+        };
+        let _ = self.outbound.send(EventFrame { event: event.into(), payload });
+    }
+
+    pub fn subscribe(&self) -> broadcast::Receiver<EventFrame> {
+        self.outbound.subscribe()
+    }
+
+    /// Listen for a named event sent *by* the client.
+    pub fn subscribe_inbound(&self, event: impl Into<String>) -> InboundSubscription {
+        let event = event.into();
+        let (tx, rx) = mpsc::unbounded_channel();
+        let mut inbound = match self.inbound.lock() {
+            Ok(inbound) => inbound,
+            Err(poisoned) => poisoned.into_inner(),
+        };
+        inbound.entry(event.clone()).or_default().push(tx);
+        drop(inbound);
+        InboundSubscription { event, rx, inbound: Arc::clone(&self.inbound) }
+    }
+
+    /// Route a frame that arrived from a tab to whoever is waiting on it.
+    pub fn dispatch_inbound(&self, frame: EventFrame) {
+        let mut inbound = match self.inbound.lock() {
+            Ok(inbound) => inbound,
+            Err(poisoned) => poisoned.into_inner(),
+        };
+        let Some(senders) = inbound.get_mut(&frame.event) else {
+            return;
+        };
+        senders.retain(|tx| tx.send(frame.payload.clone()).is_ok());
+        if senders.is_empty() {
+            inbound.remove(&frame.event);
+        }
+    }
+}