fix: pack frame at render time, send without POLLOUT dependency

- pending_bytes stores already-packed msgpack, sendable immediately
- Try sendall() directly every iteration — no POLLOUT gate
- Refresh path resends last_sent_params (not raw frame tuple)
- Router socket uses settimeout instead of setblocking for simpler I/O

scripts/led-matrix-viz.py

@@ -12,15 +12,13 @@ ROUTER_SOCK = os.environ.get("ROUTER_SOCK", "/var/run/arduino-router.sock")
 COLS = 13
 ROWS = 8
 
-REFRESH_INTERVAL = 0.2  # 5 FPS background refresh (catches dropped frames)
+REFRESH_INTERVAL = 0.2
 
 STATS_FILE = "/tmp/viz-stats.json"
 _poll = select.poll()
 POLLIN = select.POLLIN
-POLLOUT = select.POLLOUT
 
 SOCK_BUFFER = 4096
-ROUTER_RECONNECT_DELAY = 0.1
 
 
 def pack_frame(pixels):
@@ -29,8 +27,11 @@ def pack_frame(pixels):
         for col in range(COLS):
             if pixels[row][col]:
                 bits |= 1 << (row * COLS + col)
-    return (bits & 0xFFFFFFFF, (bits >> 32) & 0xFFFFFFFF,
-            (bits >> 64) & 0xFFFFFFFF, (bits >> 96) & 0xFFFFFFFF)
+    w0 = bits & 0xFFFFFFFF
+    w1 = (bits >> 32) & 0xFFFFFFFF
+    w2 = (bits >> 64) & 0xFFFFFFFF
+    w3 = (bits >> 96) & 0xFFFFFFFF
+    return [str(w0), str(w1), str(w2), str(w3)]
 
 
 def render(active_notes):
@@ -46,7 +47,7 @@ def render(active_notes):
 
 def connect_router():
     router = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
-    router.setblocking(False)
+    router.settimeout(0.3)
     try:
         router.connect(ROUTER_SOCK)
     except OSError:
@@ -54,19 +55,6 @@ def connect_router():
     return router
 
 
-def send_frame(router, packer, msg_id, frame):
-    if frame is None:
-        return msg_id
-    msg_id = (msg_id + 1) % 65535
-    params = [str(v) for v in frame]
-    req = packer.pack([0, msg_id, "draw_frame", params])
-    try:
-        router.sendall(req)
-    except (BlockingIOError, OSError):
-        pass
-    return msg_id
-
-
 def main():
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
@@ -77,18 +65,15 @@ def main():
     packer = msgpack.Packer()
 
     _poll.register(sock, POLLIN)
-    router_fd = router.fileno()
-    _poll.register(router, POLLIN | POLLOUT)
 
     active_notes = set()
-    last_sent_frame = None
-    pending_frame = None
+    last_sent_params = None
+    pending_bytes = None
     buf = b""
     msg_id = 0
 
     frames_sent = 0
     frames_dropped = 0
-    router_errors = 0
 
     last_refresh = time.monotonic()
     stats_last_write = time.monotonic()
@@ -100,14 +85,11 @@ def main():
         now = time.monotonic()
         refresh_due = (now - last_refresh) >= REFRESH_INTERVAL
 
-        timeout = 5  # ms
-
         try:
-            events = _poll.poll(timeout)
+            events = _poll.poll(5)
         except OSError:
             events = []
 
-        # Process UDP
         for fd, flags in events:
             if fd == sock.fileno() and (flags & POLLIN):
                 try:
@@ -137,38 +119,34 @@ def main():
                                 changed = True
                         if changed:
                             events_processed += 1
-                            frame = render(active_notes)
-                            if frame != last_sent_frame:
-                                pending_frame = frame
+                            params = render(active_notes)
+                            if params != last_sent_params:
+                                msg_id = (msg_id + 1) % 65535
+                                pending_bytes = packer.pack([0, msg_id, "draw_frame", params])
+                                last_sent_params = params
 
-            # Process router readable
-            if fd == router_fd and (flags & POLLIN):
-                try:
-                    while True:
-                        d = router.recv(SOCK_BUFFER)
-                        if not d:
-                            break
-                except BlockingIOError:
-                    pass
-
-        # Router writable: send pending frame immediately
-        if pending_frame is not None:
-            if any(fd == router_fd and (flags & POLLOUT) for fd, flags in events):
-                msg_id = send_frame(router, packer, msg_id, pending_frame)
-                last_sent_frame = pending_frame
-                pending_frame = None
+        # Try to send pending frame — no POLLOUT dependency
+        if pending_bytes is not None:
+            try:
+                router.sendall(pending_bytes)
+                pending_bytes = None
                 frames_sent += 1
-            else:
+            except (BlockingIOError, OSError):
                 frames_dropped += 1
 
-        # Background refresh: resend last frame to recover from router drops
+        # Background refresh: resend last params to recover from router drops
         if refresh_due:
             last_refresh = now
             fps_sample_frames += 1
-            if last_sent_frame is not None:
-                msg_id = send_frame(router, packer, msg_id, last_sent_frame)
+            if last_sent_params is not None and pending_bytes is None:
+                msg_id = (msg_id + 1) % 65535
+                refresh_bytes = packer.pack([0, msg_id, "draw_frame", last_sent_params])
+                try:
+                    router.sendall(refresh_bytes)
+                    frames_sent += 1
+                except (BlockingIOError, OSError):
+                    pass
 
-            # Write stats every 2s
             if now - stats_last_write >= 2.0:
                 fps = fps_sample_frames / (now - fps_sample_start) if (now - fps_sample_start) > 0 else 0
                 _write_stats(frames_sent, frames_dropped, fps, len(active_notes), events_processed)