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/__tests__/liveness.test.ts

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+import { describe, expect, it } from 'vitest';
+
+import { classifyLiveness, computeFleetLiveness } from '../liveness.js';
+import type { HeartbeatObservation, LivenessPolicy } from '../types.js';
+
+// Small, dev-scale policy so the arithmetic is obvious:
+//   online window = interval * missTolerance = 1000 * 2 = 2000ms
+//   dark threshold = 5000ms
+const policy: LivenessPolicy = {
+  heartbeatIntervalMs: 1000,
+  missTolerance: 2,
+  darkThresholdMs: 5000,
+};
+
+describe('classifyLiveness (deterministic, heartbeat-age based — RFC-001 §4.5)', () => {
+  it('is online when age is within interval * missTolerance', () => {
+    expect(classifyLiveness(0, policy)).toBe('online');
+    expect(classifyLiveness(1999, policy)).toBe('online');
+    expect(classifyLiveness(2000, policy)).toBe('online'); // inclusive boundary
+  });
+
+  it('is away when past the online window but before dark threshold', () => {
+    expect(classifyLiveness(2001, policy)).toBe('away');
+    expect(classifyLiveness(4999, policy)).toBe('away');
+  });
+
+  it('is offline/dark at or past the dark threshold', () => {
+    expect(classifyLiveness(5000, policy)).toBe('offline');
+    expect(classifyLiveness(50_000, policy)).toBe('offline');
+  });
+
+  it('treats a never-seen agent (Infinity age) as offline', () => {
+    expect(classifyLiveness(Number.POSITIVE_INFINITY, policy)).toBe('offline');
+  });
+
+  it('never returns online for a negative-but-huge misconfig (guards NaN)', () => {
+    // A NaN age must fail safe to offline, not silently report online.
+    expect(classifyLiveness(Number.NaN, policy)).toBe('offline');
+  });
+});
+
+describe('computeFleetLiveness (A2/A3 core)', () => {
+  const now = 100_000;
+  const obs = (slug: string, lastSeenTs: number, lastSeq = 1): HeartbeatObservation => ({
+    slug,
+    mxid: `@agent-${slug}:matrix.localhost`,
+    lastSeenTs,
+    lastSeq,
+    assertedStatus: 'online',
+  });
+
+  it('classifies a live fleet: fresh=online, stale=away, dark=offline', () => {
+    const result = computeFleetLiveness(
+      [
+        obs('alpha', now - 500), // 500ms old  -> online
+        obs('bravo', now - 3000), // 3000ms old -> away
+        obs('charlie', now - 8000), // 8000ms old -> offline
+      ],
+      now,
+      policy,
+    );
+    const byslug = Object.fromEntries(result.map((r) => [r.slug, r.status]));
+    expect(byslug).toEqual({ alpha: 'online', bravo: 'away', charlie: 'offline' });
+  });
+
+  it('A3: a previously-online agent flips to offline once age crosses dark threshold', () => {
+    const lastBeat = 100_000; // agent was hard-killed right after this beat
+    // Just before the threshold it is still merely "away"...
+    const justBefore = computeFleetLiveness([obs('victim', lastBeat, 7)], lastBeat + 4999, policy);
+    expect(justBefore[0]?.status).toBe('away');
+    // ...and the instant age reaches darkThresholdMs it is deterministically offline,
+    // with no dependence on native Matrix presence timeouts.
+    const atThreshold = computeFleetLiveness([obs('victim', lastBeat, 7)], lastBeat + 5000, policy);
+    expect(atThreshold[0]?.status).toBe('offline');
+    expect(atThreshold[0]?.ageMs).toBe(5000);
+    expect(atThreshold[0]?.lastSeq).toBe(7);
+  });
+
+  it('reports ageMs and preserves mxid/slug/seq for the human view', () => {
+    const [row] = computeFleetLiveness([obs('alpha', now - 1200, 42)], now, policy);
+    expect(row).toMatchObject({
+      slug: 'alpha',
+      mxid: '@agent-alpha:matrix.localhost',
+      ageMs: 1200,
+      lastSeq: 42,
+      status: 'online',
+    });
+  });
+});