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/heartbeat.ts

@@ -0,0 +1,124 @@
+/**
+ * `mosaic.presence` heartbeat construction and loop (RFC-001 §4.2/§4.5).
+ *
+ * The emitter is deterministic and side-effect free (easy to unit test): it
+ * owns the monotonic `seq` and stamps each beat. The loop wires the emitter to
+ * a sender on an interval; timers are injectable so the loop is testable with
+ * fake clocks.
+ */
+
+import { MACP_VERSION, type PresenceHeartbeatContent, type PresenceStatus } from './types.js';
+
+export interface HeartbeatAgentIdentity {
+  mxid: string;
+  slug: string;
+  harness: string;
+}
+
+export interface HeartbeatEmitterOptions {
+  agent: HeartbeatAgentIdentity;
+  /** Nominal interval advertised in each beat (interval_ms). */
+  intervalMs: number;
+  /** Optional mission correlation (RFC-001 §4.2 envelope). */
+  missionId?: string;
+  /** Injectable clock for deterministic tests. Default Date.now. */
+  now?: () => number;
+}
+
+/**
+ * Produces successive heartbeat contents with a monotonically increasing seq.
+ * The first `next()` returns seq=1.
+ */
+export class HeartbeatEmitter {
+  private seq = 0;
+  private readonly now: () => number;
+
+  constructor(private readonly opts: HeartbeatEmitterOptions) {
+    this.now = opts.now ?? Date.now;
+  }
+
+  /** Current sequence number (0 before the first beat). */
+  get currentSeq(): number {
+    return this.seq;
+  }
+
+  /** Build the next heartbeat content, advancing the sequence. */
+  next(status: PresenceStatus = 'online'): PresenceHeartbeatContent {
+    this.seq += 1;
+    const ts = this.now();
+    const content: PresenceHeartbeatContent = {
+      macp_version: MACP_VERSION,
+      macp_type: 'presence',
+      msgtype: 'mosaic.presence',
+      agent: {
+        mxid: this.opts.agent.mxid,
+        slug: this.opts.agent.slug,
+        harness: this.opts.agent.harness,
+      },
+      ts,
+      body: `${this.opts.agent.slug} ${status} (seq ${this.seq})`,
+      status,
+      seq: this.seq,
+      interval_ms: this.opts.intervalMs,
+    };
+    if (this.opts.missionId !== undefined) {
+      content.mission_id = this.opts.missionId;
+    }
+    return content;
+  }
+}
+
+export type HeartbeatSender = (content: PresenceHeartbeatContent) => void | Promise<void>;
+
+export interface HeartbeatLoopOptions {
+  emitter: HeartbeatEmitter;
+  send: HeartbeatSender;
+  intervalMs: number;
+  /** Status supplier evaluated each beat. Default: always 'online'. */
+  status?: () => PresenceStatus;
+  /** Called if a beat's send rejects (so a transient failure doesn't kill the loop). */
+  onError?: (err: unknown) => void;
+  /** Injectable timer (tests). Defaults to global setInterval/clearInterval. */
+  setIntervalFn?: (cb: () => void, ms: number) => unknown;
+  clearIntervalFn?: (handle: unknown) => void;
+}
+
+/** A running heartbeat loop; call stop() to end it. */
+export interface HeartbeatLoopHandle {
+  stop: () => void;
+}
+
+/**
+ * Start a heartbeat loop: emits one beat immediately, then every intervalMs.
+ * Returns a handle whose `stop()` is idempotent.
+ */
+export function startHeartbeatLoop(opts: HeartbeatLoopOptions): HeartbeatLoopHandle {
+  const status = opts.status ?? (() => 'online' as PresenceStatus);
+  const onError = opts.onError ?? (() => {});
+  const setIntervalFn = opts.setIntervalFn ?? ((cb, ms) => setInterval(cb, ms));
+  const clearIntervalFn =
+    opts.clearIntervalFn ?? ((h) => clearInterval(h as ReturnType<typeof setInterval>));
+
+  const beat = (): void => {
+    try {
+      const result = opts.send(opts.emitter.next(status()));
+      if (result instanceof Promise) {
+        result.catch(onError);
+      }
+    } catch (err) {
+      onError(err);
+    }
+  };
+
+  beat(); // immediate first beat so liveness is fresh at once
+  const handle = setIntervalFn(beat, opts.intervalMs);
+
+  let stopped = false;
+  return {
+    stop: () => {
+      if (stopped) return;
+      stopped = true;
+      clearIntervalFn(handle);
+    },
+  };
+}