feat: broadcast Timmy state changes via WS relay (#380)

Co-authored-by: Kimi Agent <kimi@timmy.local>
Co-committed-by: Kimi Agent <kimi@timmy.local>

src/timmy/workshop_state.py

@@ -11,6 +11,7 @@ import asyncio
 import hashlib
 import json
 import logging
+from collections.abc import Awaitable, Callable
 from datetime import UTC, datetime
 from pathlib import Path
 
@@ -91,12 +92,14 @@ class WorkshopHeartbeat:
         self,
         interval: int = HEARTBEAT_INTERVAL,
         path: Path | None = None,
+        on_change: Callable[[dict], Awaitable[None]] | None = None,
     ) -> None:
         self._interval = interval
         self._path = path or PRESENCE_FILE
         self._last_hash: str | None = None
         self._task: asyncio.Task | None = None
         self._trigger = asyncio.Event()
+        self._on_change = on_change
 
     async def start(self) -> None:
         """Start the heartbeat background loop."""
@@ -129,13 +132,13 @@ class WorkshopHeartbeat:
                 except TimeoutError:
                     pass  # Normal periodic tick
 
-                self._write_if_changed()
+                await self._write_if_changed()
             except asyncio.CancelledError:
                 raise
             except Exception as exc:
                 logger.error("Workshop heartbeat error: %s", exc)
 
-    def _write_if_changed(self) -> None:
+    async def _write_if_changed(self) -> None:
         """Build state, compare hash, write only if changed."""
         state_dict = get_state_dict()
         current_hash = _state_hash(state_dict)
@@ -143,6 +146,11 @@ class WorkshopHeartbeat:
             return
         self._last_hash = current_hash
         write_state(state_dict, self._path)
+        if self._on_change:
+            try:
+                await self._on_change(state_dict)
+            except Exception as exc:
+                logger.warning("on_change callback failed: %s", exc)
 
     def _subscribe_to_events(self) -> None:
         """Subscribe to cognitive state change events on the sensory bus."""