feat(comms): P1 presence — minimal Synapse + fleet presence room + mosaic.presence heartbeat + liveness (#888)

Co-authored-by: jason.woltje <jason@diversecanvas.com>
Co-committed-by: jason.woltje <jason@diversecanvas.com>

packages/comms/src/liveness-reader.ts

@@ -0,0 +1,58 @@
+/**
+ * Fleet liveness reader (RFC-001 §4.5, A2/A4).
+ *
+ * Reads `mosaic.presence` heartbeats from the fleet presence room and computes
+ * deterministic online/away/offline for every agent. This is the surface a
+ * human (or the escalation watchdog, P2+) reads to answer "who's alive?".
+ */
+
+import { computeFleetLiveness } from './liveness.js';
+import type { MinimalMatrixClient } from './matrix-client.js';
+import { DEFAULT_LIVENESS_POLICY, type AgentLiveness, type LivenessPolicy } from './types.js';
+
+export interface FleetLivenessReaderOptions {
+  client: MinimalMatrixClient;
+  /** The fleet presence room (id or resolved id). */
+  roomId: string;
+  policy?: LivenessPolicy;
+  /** Injectable clock for tests. Default Date.now. */
+  now?: () => number;
+  /** How many timeline events to scan back. Default 200. */
+  scanLimit?: number;
+}
+
+export class FleetLivenessReader {
+  private readonly policy: LivenessPolicy;
+  private readonly now: () => number;
+
+  constructor(private readonly opts: FleetLivenessReaderOptions) {
+    this.policy = opts.policy ?? DEFAULT_LIVENESS_POLICY;
+    this.now = opts.now ?? Date.now;
+  }
+
+  /** Read the room and compute current liveness for every seen agent. */
+  async read(): Promise<AgentLiveness[]> {
+    const observations = await this.opts.client.readHeartbeats(
+      this.opts.roomId,
+      this.opts.scanLimit ?? 200,
+    );
+    return computeFleetLiveness(observations, this.now(), this.policy);
+  }
+
+  /** A compact human-readable liveness board (A4 CLI view). */
+  async formatBoard(): Promise<string> {
+    const rows = await this.read();
+    rows.sort((a, b) => a.slug.localeCompare(b.slug));
+    const dot: Record<string, string> = { online: '🟢', away: '🟡', offline: '🔴' };
+    const lines = rows.map(
+      (r) =>
+        `${dot[r.status] ?? '⚪'} ${r.slug.padEnd(16)} ${r.status.padEnd(8)} ` +
+        `age=${(r.ageMs / 1000).toFixed(1)}s seq=${r.lastSeq} ${r.mxid}`,
+    );
+    const summary =
+      `online=${rows.filter((r) => r.status === 'online').length} ` +
+      `away=${rows.filter((r) => r.status === 'away').length} ` +
+      `offline=${rows.filter((r) => r.status === 'offline').length}`;
+    return [`Fleet presence — ${summary}`, ...lines].join('\n');
+  }
+}