G3.1: dedicated bridge heartbeat — watchdog liveness independent of audio loop

src-tauri/src/shm.rs

@@ -63,6 +63,10 @@ pub struct SharedAudioBufferIPC {
     // Append-only field — offsets of control_queue (2836) and
     // control_queue_count (11156) are unchanged.
     pub attach_in_flight: u32,
+    // G3.1: dedicated heartbeat — incremented ~10Hz by a bridge thread
+    // independent of the audio loop. Watchdog liveness keys on this.
+    // Append-only field: offsets above are unchanged.
+    pub heartbeat: u32,
 }
 
 pub struct Shm {
@@ -166,6 +170,10 @@ impl Shm {
     pub fn attach_in_flight(&self) -> bool {
         self.ipc().attach_in_flight != 0
     }
+
+    pub fn heartbeat(&self) -> u32 {
+        self.ipc().heartbeat
+    }
 }
 
 impl Drop for Shm {
@@ -188,6 +196,6 @@ mod tests {
         // native_bridge/tests/shm_selfcheck.cpp asserts the same sizes.
         assert_eq!(std::mem::size_of::<MidiEventIPC>(), 12);
         assert_eq!(std::mem::size_of::<ControlEventIPC>(), 1040);
-        assert_eq!(std::mem::size_of::<SharedAudioBufferIPC>(), 11164);
+        assert_eq!(std::mem::size_of::<SharedAudioBufferIPC>(), 11168);
     }
 }