feat(matrix-bridge-dagi): add backpressure queue with N workers (H2)

Reader + N workers architecture:
  Reader: sync_poll → rate_check → dedupe → queue.put_nowait()
  Workers (WORKER_CONCURRENCY, default 2): queue.get() → invoke → send → audit

Drop policy (queue full):
  - put_nowait() raises QueueFull → dropped immediately (reader never blocks)
  - audit matrix.queue_full + on_queue_dropped callback
  - metric: matrix_bridge_queue_dropped_total{room_id,agent_id}

Graceful shutdown:
  1. stop_event → reader exits loop
  2. queue.join() with QUEUE_DRAIN_TIMEOUT_S (default 5s) → workers finish in-flight
  3. worker tasks cancelled

New config env vars:
  QUEUE_MAX_EVENTS (default 100)
  WORKER_CONCURRENCY (default 2)
  QUEUE_DRAIN_TIMEOUT_S (default 5)

New metrics (H3 additions):
  matrix_bridge_queue_size (gauge)
  matrix_bridge_queue_dropped_total (counter)
  matrix_bridge_queue_wait_seconds histogram (buckets: 0.01…30s)

/health: queue.size, queue.max, queue.workers
MatrixIngressLoop: queue_size + worker_count properties

6 queue tests: enqueue/process, full-drop-audit, concurrency barrier,
graceful drain, wait metric, rate-limit-before-enqueue
Total: 71 passed

Made-with: Cursor

services/matrix-bridge-dagi/app/config.py

@@ -29,6 +29,11 @@ class BridgeConfig:
     rate_limit_room_rpm: int       # max messages per room per minute
     rate_limit_sender_rpm: int     # max messages per sender per minute
 
+    # H2: Backpressure queue
+    queue_max_events: int          # max pending items (drops oldest on full)
+    worker_concurrency: int        # parallel invoke workers
+    queue_drain_timeout_s: float   # graceful shutdown drain timeout
+
     # Service identity
     node_id: str
     build_sha: str
@@ -62,6 +67,9 @@ def load_config() -> BridgeConfig:
         bridge_allowed_agents=allowed,
         rate_limit_room_rpm=int(_optional("RATE_LIMIT_ROOM_RPM", "20")),
         rate_limit_sender_rpm=int(_optional("RATE_LIMIT_SENDER_RPM", "10")),
+        queue_max_events=max(1, int(_optional("QUEUE_MAX_EVENTS", "100"))),
+        worker_concurrency=max(1, int(_optional("WORKER_CONCURRENCY", "2"))),
+        queue_drain_timeout_s=max(1.0, float(_optional("QUEUE_DRAIN_TIMEOUT_S", "5"))),
         node_id=_optional("NODE_ID", "NODA1"),
         build_sha=_optional("BUILD_SHA", "dev"),
         build_time=_optional("BUILD_TIME", "local"),