fix(huddle): prevent phantom huddle from late-arriving relay events

[tlongwell-block]

Problem

After ending a huddle, HuddleIndicator shows a phantom huddle with 1 participant — the green headphone icon stays lit indefinitely even though no one is in the huddle.

Root cause

The relay emits a 48102 (participant left) when the audio WebSocket disconnects, which happens ~1 second after the client emits 48103 (huddle ended) via end_huddle. When reconstruct() replays these events in created_at order, the sequence is:

48100 started → 48101 joined → ... → 48103 ended → 48102 left

The 48103 correctly sets huddle = null. But the 48102 that follows hits the "infer huddle exists" fallback — when huddle is null, the join/left handlers assume the start event fell out of the subscription window and re-create the huddle. This produces an ActiveHuddle with an empty participant set, which displays as 1 participant due to Math.max(1, 0).

Confirmed in staging

The huddle-test channel on Blox staging had exactly this event sequence in the DB:

48100 started  (21:41:46)
48101 joined   (21:41:47)
48101 joined   (21:53:17)  ← reconnect
48102 left     (21:53:44)
48103 ended    (21:59:56)  ← client-side end_huddle
48102 left     (21:59:57)  ← relay-emitted, 1s later — resurrects phantom

Fix

Track which ephemeral channel IDs have been ended in a local endedChannels Set during reconstruction. Join and left events for an ended channel are skipped instead of triggering the inference fallback.

Three changes to reconstruct():

1. endedChannels Set — tracks ephemeral channel IDs that have received a 48103 event
2. Guard on join/left handlers — if (endedChannels.has(ephId)) break skips the inference fallback for ended channels
3. Less restrictive ENDED handler — now records the ended state even when huddle is already null (covers the case where the ended event survives in the subscription window but the corresponding started event does not)
4. STARTED clears ended state — endedChannels.delete(ephId) so a new huddle on the same ephemeral channel ID works correctly

The endedChannels Set is function-local (rebuilt on every reconstruct() call) and bounded by the subscription window (limit: 100 events).

Changes

• desktop/src/features/huddle/components/HuddleIndicator.tsx — +16/-2 lines

Testing

• biome check — clean
• Codex CLI review: APPROVED 9/10
• Verified against the exact event sequence from the staging DB