perf(aw): run ActivityWatch polling in background thread to eliminate UI freezes

Synchronous urllib calls in the 60 FPS main loop caused a 3-second network
connect timeout every 5 seconds whenever ActivityWatch was offline (due to
Windows IPv6/IPv4 localhost resolution). This completely froze the main thread,
stalled the Windows message pump, and triggered Windows Hung-App detection
(hourglass / wait cursor).

ActivityWatchClient now polls in a dedicated daemon worker thread:
- All socket connections and HTTP timeouts occur in the background thread.
- get_current_window_event() reads cached state in 0ms without blocking.
- Fallback to native Win32 window APIs is immediate with zero latency.

catser/activitywatch.py

@@ -40,30 +40,68 @@ class DistractionEvent:
             self.timestamp = time.time()
 
 
+import threading
+
 class ActivityWatchClient:
     """
     Client interface for ActivityWatch API with automatic native Win32 fallback.
+    Runs all HTTP requests in a background thread so that network latency or
+    timeouts when ActivityWatch is offline NEVER block the 60 FPS animation loop.
     """
 
     def __init__(self, config: Config):
         self.config = config
-        self.base_url = config.aw_url.rstrip("/")
+        # Normalise localhost to 127.0.0.1 to prevent Windows IPv6 resolution timeouts
+        url = config.aw_url.rstrip("/")
+        if "localhost" in url:
+            url = url.replace("localhost", "127.0.0.1")
+        self.base_url = url
         self.api_url = f"{self.base_url}/api/0"
         self.bucket_id: Optional[str] = None
         self.is_connected: bool = False
-        self.last_connect_attempt: float = 0.0
         self.connect_retry_delay: float = 5.0  # Retry connecting every 5s
 
-    def check_connection(self) -> bool:
-        """Pings the ActivityWatch /api/0/info endpoint."""
-        now = time.time()
-        if now - self.last_connect_attempt < self.connect_retry_delay and not self.is_connected:
-            return False
+        self._latest_event: Optional[Dict[str, Any]] = None
+        self._lock = threading.Lock()
+        self._running = True
+        self._worker_thread = threading.Thread(
+            target=self._background_worker,
+            name="ActivityWatchWorker",
+            daemon=True,
+        )
+        self._worker_thread.start()
 
-        self.last_connect_attempt = now
+    def _background_worker(self) -> None:
+        """
+        Runs in the background, continuously attempting connection and polling
+        ActivityWatch without ever touching or blocking the main GUI thread.
+        """
+        while self._running:
             try:
-            req = urllib.request.Request(f"{self.api_url}/info")
-            with urllib.request.urlopen(req, timeout=1.5) as resp:
+                if not self.is_connected or not self.bucket_id:
+                    self._attempt_connect()
+
+                if self.is_connected and self.bucket_id:
+                    ev = self._fetch_latest_event()
+                    with self._lock:
+                        self._latest_event = ev
+                else:
+                    with self._lock:
+                        self._latest_event = None
+            except Exception as e:
+                logger.debug(f"AW worker error: {e}")
+                self.is_connected = False
+                with self._lock:
+                    self._latest_event = None
+
+            sleep_time = self.config.poll_interval_sec if self.is_connected else self.connect_retry_delay
+            time.sleep(sleep_time)
+
+    def _attempt_connect(self) -> bool:
+        """Pings the ActivityWatch /api/0/info endpoint with a short timeout."""
+        try:
+            req = urllib.request.Request(f"{self.api_url}/info", headers={"User-Agent": "Catser"})
+            with urllib.request.urlopen(req, timeout=0.8) as resp:
                 if resp.status == 200:
                     data = json.loads(resp.read().decode("utf-8"))
                     logger.info(f"Connected to ActivityWatch server v{data.get('version', 'unknown')}")
@@ -72,17 +110,16 @@ class ActivityWatchClient:
                     return True
         except Exception:
             if self.is_connected:
-                logger.warning("ActivityWatch server disconnected. Falling back to native tracking.")
+                logger.warning("ActivityWatch disconnected. Falling back to native tracking.")
             self.is_connected = False
             return False
-
         return False
 
     def _discover_window_bucket(self) -> Optional[str]:
         """Discovers the active 'aw-watcher-window_*' bucket."""
         try:
-            req = urllib.request.Request(f"{self.api_url}/buckets")
-            with urllib.request.urlopen(req, timeout=2.0) as resp:
+            req = urllib.request.Request(f"{self.api_url}/buckets", headers={"User-Agent": "Catser"})
+            with urllib.request.urlopen(req, timeout=0.8) as resp:
                 if resp.status == 200:
                     buckets = json.loads(resp.read().decode("utf-8"))
                     for b_id in buckets.keys():
@@ -91,22 +128,17 @@ class ActivityWatchClient:
                             logger.info(f"Using ActivityWatch window bucket: {self.bucket_id}")
                             return self.bucket_id
         except Exception as e:
-            logger.warning(f"Error querying ActivityWatch buckets: {e}")
+            logger.debug(f"Error querying ActivityWatch buckets: {e}")
         return None
 
-    def get_current_window_event(self) -> Optional[Dict[str, Any]]:
-        """
-        Fetches the latest window event from ActivityWatch.
-        Returns dict with 'app' and 'title', or None.
-        """
-        if not self.is_connected or not self.bucket_id:
-            if not self.check_connection() or not self.bucket_id:
+    def _fetch_latest_event(self) -> Optional[Dict[str, Any]]:
+        """Fetches the latest event from the active window bucket."""
+        if not self.bucket_id:
             return None
-
         try:
             url = f"{self.api_url}/buckets/{self.bucket_id}/events?limit=1"
-            req = urllib.request.Request(url)
-            with urllib.request.urlopen(req, timeout=1.5) as resp:
+            req = urllib.request.Request(url, headers={"User-Agent": "Catser"})
+            with urllib.request.urlopen(req, timeout=0.8) as resp:
                 if resp.status == 200:
                     events = json.loads(resp.read().decode("utf-8"))
                     if events and isinstance(events, list) and len(events) > 0:
@@ -119,9 +151,24 @@ class ActivityWatchClient:
         except Exception as e:
             logger.debug(f"ActivityWatch query error: {e}")
             self.is_connected = False
-
         return None
 
+    def check_connection(self) -> bool:
+        """Returns connection status immediately without blocking."""
+        return self.is_connected
+
+    def get_current_window_event(self) -> Optional[Dict[str, Any]]:
+        """
+        Returns the latest window event from the background cache.
+        Completely non-blocking (0ms latency).
+        """
+        with self._lock:
+            return self._latest_event
+
+    def stop(self) -> None:
+        """Signals the background worker to exit."""
+        self._running = False
+
     def check_for_distraction(self) -> Optional[DistractionEvent]:
         """
         Checks current active window against distraction rules.