feat(comms): P1 presence — minimal Synapse + fleet presence room + mosaic.presence heartbeat + liveness

Implements RFC-001 P1 (the first shippable slice): deterministic Matrix
presence/liveness on a single-instance dev Synapse.

- infra/matrix/: DEV Synapse (RFC-002 Mode B, federation OFF, self-signed TLS,
  enable_registration:false, appservice registration wired). Rendered from
  parameterized templates — zero hardcoded topology. .data is gitignored.
- packages/comms/: minimal MACP presence SDK — set presence, run the
  mosaic.presence heartbeat (seq + interval per RFC-001 §4.5), and a
  deterministic liveness reader (online/away/offline from heartbeat age, NOT
  native-presence-timeout). Liveness core written RED-FIRST. 19 vitest tests.
- tools/matrix-presence-harness/: minimal provisioner (registers >=3 agent
  MXIDs, creates the fleet presence room, joins them — reuses the existing
  @mosaicstack/appservice intent lib) + an E2E validation harness proving
  A2/A3/A4 against a real Synapse.
- eslint.config.mjs: register packages/comms/vitest.config.ts with the
  type-aware project service (same as other packages' vitest configs).

DEV-compose validated only; production deploy is a separate coordinated step
(deploy-holds respected).

Part of the comms-evolution program (RFC-001 P1)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0158NZqN2n2ymKFeJAZ4GUCb

packages/comms/README.md

@@ -0,0 +1,41 @@
+# @mosaicstack/comms
+
+MACP presence SDK — the **P1 (presence)** slice of RFC-001 (§4.5 liveness,
+§4.2 event envelope). Minimal by design: set Matrix presence, run the
+`mosaic.presence` heartbeat, and compute **deterministic** fleet liveness.
+
+Out of P1 scope (later phases): enrollment/auto-detect, room taxonomy,
+per-agent token minting, signed-authorship, federation.
+
+## API
+
+- `classifyLiveness(ageMs, policy)` / `computeFleetLiveness(observations, now, policy)`
+  — pure, deterministic online/away/offline from heartbeat age. The
+  authoritative liveness source (RFC-001 §4.5): native Matrix presence is _not_
+  relied upon.
+- `HeartbeatEmitter` / `startHeartbeatLoop(...)` — build and drive the
+  `mosaic.presence` heartbeat (monotonic `seq`, `interval_ms`).
+- `MinimalMatrixClient` — tiny C-S client: `setPresence`, `sendHeartbeat`,
+  `readHeartbeats`, `joinRoom`. Supports Application-Service masquerade
+  (`actAsUserId`) for the P1 provisioner, or a per-agent `accessToken`.
+- `PresenceAgent` — high-level: join the fleet room, go present, heartbeat.
+  `pauseHeartbeat()` models a crash (no graceful signal).
+- `FleetLivenessReader` — reads the fleet room and computes the liveness board
+  (`read()` / `formatBoard()`), the surface a human or watchdog reads.
+
+## Liveness policy (RFC-001 §4.5)
+
+```
+online : age <= heartbeatIntervalMs * missTolerance
+away   : age <  darkThresholdMs
+offline: otherwise (or never-seen / non-finite age -> fail safe to offline)
+```
+
+Defaults: interval 30s, miss-tolerance 2, dark-threshold 10min
+(`DEFAULT_LIVENESS_POLICY`). All runtime-tunable per RFC-002 §5.3.
+
+## Tests
+
+`pnpm --filter @mosaicstack/comms test` — the liveness core is written
+RED-FIRST; an end-to-end proof against a real Synapse lives in
+`tools/matrix-presence-harness`.