fix: event-driven viz with immediate rendering, zero decay, clean stats

Rewrite led-matrix-viz.py to eliminate latency:
- Render and pack frame immediately on each MIDI event
- Send on next poll cycle (no POLLOUT dependency, no frame loop)
- Notes on/off purely from MIDI data — zero decay
- Background 5 FPS refresh for router drop recovery
- Clean stats: FPS, active_notes, midi_events, bytes_received, raw_packets

scripts/led-matrix-viz.py

@@ -82,9 +82,6 @@ def main():
     fps_sample_frames = 0
     events_processed = 0
     raw_packets = 0
-    semicolon_hits = 0
-    midi_matched = 0
-    changed_true = 0
 
     while True:
         now = time.monotonic()
@@ -107,42 +104,30 @@ def main():
                     pass
 
                 while b";" in buf:
-                    semicolon_hits += 1
                     raw_msg, buf = buf.split(b";", 1)
                     msg = raw_msg.decode().strip()
                     parts = msg.split()
-                    if not parts:
+                    if len(parts) >= 3 and parts[0] == "midi":
-                        print(f"[viz] empty parts: {msg!r}", flush=True)
+                        status = int(parts[1])
-                        continue
+                        note = int(parts[2])
-                    if parts[0] != "midi":
+                        vel = int(parts[3]) if len(parts) >= 4 else 0
-                        print(f"[viz] not midi: {msg!r}", flush=True)
+                        msg_type = status & 0xF0
-                        continue
+                        changed = False
-                    if len(parts) < 3:
+                        if msg_type == 0x90 and vel > 0:
-                        print(f"[viz] too short: {parts}", flush=True)
+                            if note not in active_notes:
-                        continue
+                                active_notes.add(note)
-                    midi_matched += 1
+                                changed = True
-                    status = int(parts[1])
+                        elif msg_type == 0x80 or (msg_type == 0x90 and vel == 0):
-                    note = int(parts[2])
+                            if note in active_notes:
-                    vel = int(parts[3]) if len(parts) >= 4 else 0
+                                active_notes.discard(note)
-                    msg_type = status & 0xF0
+                                changed = True
-                    changed = False
+                        if changed:
-                    if msg_type == 0x90 and vel > 0:
+                            events_processed += 1
-                        if note not in active_notes:
+                            params = render(active_notes)
-                            active_notes.add(note)
+                            if params != last_sent_params:
-                            changed = True
+                                msg_id = (msg_id + 1) % 65535
-                    elif msg_type == 0x80 or (msg_type == 0x90 and vel == 0):
+                                pending_bytes = packer.pack([0, msg_id, "draw_frame", params])
-                        if note in active_notes:
+                                last_sent_params = params
-                            active_notes.discard(note)
-                            changed = True
-                    if changed:
-                        changed_true += 1
-                        events_processed += 1
-                        print(f"[viz] note {note} {'on' if vel > 0 else 'off'} events={events_processed}", flush=True)
-                        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
 
         # Try to send pending frame — no POLLOUT dependency
         if pending_bytes is not None:
@@ -168,14 +153,14 @@ def main():
 
             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, bytes_received, raw_packets, semicolon_hits, midi_matched, changed_true)
+                _write_stats(frames_sent, frames_dropped, fps, len(active_notes), events_processed, bytes_received, raw_packets)
                 stats_last_write = now
                 fps_sample_start = now
                 fps_sample_frames = 0
                 events_processed = 0
 
 
-def _write_stats(sent, dropped, fps, active_count, events, bytes_rcv, packets, semi, matched, changed):
+def _write_stats(sent, dropped, fps, active_count, events, bytes_rcv, packets):
     import json
     try:
         with open(STATS_FILE, "w") as f:
@@ -187,9 +172,6 @@ def _write_stats(sent, dropped, fps, active_count, events, bytes_rcv, packets, s
                 "midi_events": events,
                 "bytes_received": bytes_rcv,
                 "raw_packets": packets,
-                "semicolon_hits": semi,
-                "midi_matched": matched,
-                "changed_true": changed,
                 "ts": time.time()
             }, f)
     except OSError: