Phase 4: shared-write hardening + group lenses

- vault_lock gains bounded retry/backoff (CHORUS_LOCK_RETRIES=4,
  CHORUS_LOCK_BACKOFF=0.5s); atomic_index_update and recall-index upkeep
  retry acquisition — unlocked fallback only after exhausted retries,
  loudly, so an already-written note is never stranded unindexed.
- Duplicate-gate candidates carry the existing note's author; STOP
  message says whose entity the capture collided with.
- recall --author <member> filters hits + linked context to one member's
  notes; recall briefs and --json surface the author: stamp.
- load --all-members appends a group-wide view (every member's scope +
  last-session heartbeat); roster parsing accepts folders as
  trailing-slash file entries (the REST API's actual shape).
- operating-contract.md concurrency section rewritten for N members.
- Two-member e2e suite committed as eval/test_multimember.py (26 checks
  incl. all four Phase-4 behaviors).
- Manifest -> 2.0.0-alpha.4; rebuilt chorus-memory.plugin.

Verified: 25/25 unit, scaffold, routing-sync, 5 mock e2e suites (incl.
new multimember), run_eval metrics unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

chorus-memory.plugin.src/commands/chorus-recall.md

@@ -12,7 +12,7 @@ Run the one-call recall — it resolves the term against the entity index, searc
 ```bash
 CHORUS="${CLAUDE_PLUGIN_ROOT}/skills/chorus-memory/scripts/chorus.py"
 [ -f "$CHORUS" ] || CHORUS=$(ls /sessions/*/mnt/.remote-plugins/*/skills/chorus-memory/scripts/chorus.py 2>/dev/null | head -1)   # CoWork sandbox fallback
-python3 "$CHORUS" recall "$ARGUMENTS"
+python3 "$CHORUS" recall "$ARGUMENTS"   # add --author <member> to filter to one member's notes
 # Windows: use `python` or `py -3` if `python3` is not on PATH.
 ```