Push a state snapshot only for events that change it

The hub sent every open tab a full snapshot on every StateEvent, LED writes
included - placing and removing a figure was 13 snapshots, 9 of them for LED
changes the snapshot does not even contain. List the events that matter, and make
a test fail when a new StateEvent is sorted into neither list.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

python-backend/musicmouse/services/web/hub.py

@@ -22,7 +22,19 @@ from typing import Any
 from fastapi import WebSocket
 
 from musicmouse.app import App
-from musicmouse.events import Event, StateEvent, ToggleClockRequested
+from musicmouse.events import (
+    ActiveFigureChanged,
+    ClockStateChanged,
+    ConnectionChanged,
+    Event,
+    FigureSelectionChanged,
+    LedEffectChanged,
+    PlaybackChanged,
+    StateEvent,
+    ToggleClockRequested,
+    TrackChanged,
+    VolumeChanged,
+)
 from musicmouse.services.web.state import snapshot
 
 _log = logging.getLogger(__name__)
@@ -33,6 +45,25 @@ __all__ = ["StateHub"]
 #: enough to leave running.
 POSITION_INTERVAL = 0.5
 
+#: The state events that change something in :func:`~musicmouse.services.web.state.snapshot`
+#: - each one costs every open tab a full snapshot. LED writes are the reason this is a
+#: list rather than "every StateEvent": a figure placed and removed is 9 LED writes,
+#: and the snapshot has no LED state in it.
+SNAPSHOT_EVENTS: tuple[type[StateEvent], ...] = (
+    PlaybackChanged,
+    TrackChanged,
+    VolumeChanged,
+    ActiveFigureChanged,
+    ConnectionChanged,
+    ClockStateChanged,
+)
+
+#: State events deliberately not pushed to the browser. Together with
+#: :data:`SNAPSHOT_EVENTS` this covers every :class:`StateEvent`; a test holds that, so
+#: a new state event has to be sorted into one or the other.
+#: The ring's album picker is shown on the LED ring, not in the browser.
+IGNORED_EVENTS: tuple[type[StateEvent], ...] = (LedEffectChanged, FigureSelectionChanged)
+
 
 class StateHub:
     def __init__(self, app: App) -> None:
@@ -44,7 +75,7 @@ class StateHub:
 
     def start(self) -> None:
         self._unsubscribe = [
-            self.app.bus.subscribe(StateEvent, self._on_state),
+            *(self.app.bus.subscribe(kind, self._on_state) for kind in SNAPSHOT_EVENTS),
             # The clock overlay is the kiosk's own; the remote's key only asks for it.
             self.app.bus.subscribe(ToggleClockRequested, self._on_clock_toggle),
         ]