feat(federation): detect peer reset on needs_attention peers (§4.1)

A reset peer can reach needs_attention via the auth-failure path (HTTP up,
401/403 from a new incarnation crossing AUTH_FAILURE_THRESHOLD) without ever
passing through unreachable, so the unreachable-only recovery probe never
observes its epoch change and no reset journal is created — leaving a later
manual Re-peer with nothing to heal.

Add detectResetOnNeedsAttentionPeers() to the 15-minute health-check tick:
probe needs_attention peers with a non-null baseline (excluding those already
peer_reset_detected) and call markPeerReset on an observed epoch mismatch.
Detection only — never recovers a needs_attention peer to active; baseline
(peer_instance_id) and hmac_secret untouched.

packages/server/src/utils/federationRecovery.test.ts

@@ -150,4 +150,88 @@ describe('federationRecovery primitives', () => {
     // A reset peer must NOT be recovered to active.
     expect(onPeerActivated).not.toHaveBeenCalled();
   });
+
+  // ── detectResetOnNeedsAttentionPeers (design §4.1) ─────────────────────────
+  // Closes the auth-failure sub-case: a reset peer whose HTTP is up (returning
+  // 401/403 because the new incarnation has no peer row for us) crosses
+  // AUTH_FAILURE_THRESHOLD and lands in `needs_attention` WITHOUT ever passing
+  // through `unreachable`, so the unreachable-only recovery probe never observes
+  // its epoch change. This pass probes those peers too — detection ONLY, never a
+  // recover-to-active.
+  function seedNeedsAttention(id: string, reason: string | null, peerInstanceId: string | null): void {
+    testDb.insert(schema.federationPeers).values({
+      id, origin: 'https://peer.example', hmacSecret: 'secret',
+      status: 'needs_attention', needsAttentionReason: reason,
+      peerInstanceId, consecutiveFailures: 0,
+      lastSyncedAt: Date.now(), createdAt: Date.now(),
+    }).run();
+  }
+
+  it('detectResetOnNeedsAttentionPeers flags an auth-failure peer whose epoch changed (detection only)', async () => {
+    seedNeedsAttention('peer-na', 'auth_failures', 'E0');
+    // A pure replicated stub belonging to the dead incarnation (bare-domain home).
+    testDb.insert(schema.users).values({
+      id: 'stub-1', username: 'carol', displayName: 'carol',
+      passwordHash: '!federation-replicated', homeInstance: 'peer.example',
+      createdAt: Date.now(),
+    }).run();
+    vi.spyOn(globalThis, 'fetch').mockResolvedValue(new Response('{"instanceId":"E1"}', { status: 200 }));
+
+    const { detectResetOnNeedsAttentionPeers } = await import('./federationRecovery.js');
+    await detectResetOnNeedsAttentionPeers();
+
+    const row = testDb.select().from(schema.federationPeers)
+      .where(eq(schema.federationPeers.id, 'peer-na')).get()!;
+    expect(row.status).toBe('needs_attention'); // NOT flipped to active
+    expect(row.needsAttentionReason).toBe('peer_reset_detected');
+    expect(row.observedPeerInstanceId).toBe('E1'); // observed epoch recorded
+    expect(row.peerInstanceId).toBe('E0'); // trusted baseline untouched
+    expect(row.hmacSecret).toBe('secret'); // secret untouched
+
+    const journal = testDb.select().from(schema.federationResetEvents)
+      .where(eq(schema.federationResetEvents.origin, 'https://peer.example')).get()!;
+    expect(journal.deadEpoch).toBe('E0');
+    expect(journal.resolvedAt).toBeNull();
+
+    const stub = testDb.select().from(schema.users)
+      .where(eq(schema.users.id, 'stub-1')).get()!;
+    expect(stub.federationHealPending).toBe(1); // dead incarnation snapshotted
+
+    expect(onPeerActivated).not.toHaveBeenCalled(); // detection only
+  });
+
+  it('detectResetOnNeedsAttentionPeers is a no-op when the probed epoch matches the baseline', async () => {
+    seedNeedsAttention('peer-same', 'auth_failures', 'E0');
+    vi.spyOn(globalThis, 'fetch').mockResolvedValue(new Response('{"instanceId":"E0"}', { status: 200 }));
+
+    const { detectResetOnNeedsAttentionPeers } = await import('./federationRecovery.js');
+    await detectResetOnNeedsAttentionPeers();
+
+    const row = testDb.select().from(schema.federationPeers)
+      .where(eq(schema.federationPeers.id, 'peer-same')).get()!;
+    expect(row.status).toBe('needs_attention');
+    expect(row.needsAttentionReason).toBe('auth_failures'); // unchanged
+    expect(testDb.select().from(schema.federationResetEvents).all()).toHaveLength(0);
+    expect(onPeerActivated).not.toHaveBeenCalled();
+  });
+
+  it('detectResetOnNeedsAttentionPeers skips peers already flagged peer_reset_detected (no probe)', async () => {
+    seedNeedsAttention('peer-done', 'peer_reset_detected', 'E0');
+    const spy = vi.spyOn(globalThis, 'fetch');
+
+    const { detectResetOnNeedsAttentionPeers } = await import('./federationRecovery.js');
+    await detectResetOnNeedsAttentionPeers();
+
+    expect(spy).not.toHaveBeenCalled(); // already journaled — not re-probed
+  });
+
+  it('detectResetOnNeedsAttentionPeers skips peers with a null baseline (nothing to compare)', async () => {
+    seedNeedsAttention('peer-nobase', 'auth_failures', null);
+    const spy = vi.spyOn(globalThis, 'fetch');
+
+    const { detectResetOnNeedsAttentionPeers } = await import('./federationRecovery.js');
+    await detectResetOnNeedsAttentionPeers();
+
+    expect(spy).not.toHaveBeenCalled(); // no trusted baseline → cannot detect a change
+  });
 });

packages/server/src/utils/federationRecovery.ts

@@ -1,6 +1,6 @@
 import { getDb } from '../db/index.js';
 import * as schema from '../db/schema.js';
-import { eq } from 'drizzle-orm';
+import { and, eq, isNotNull, isNull, ne, or } from 'drizzle-orm';
 import { onPeerActivated } from './federationPeerActivation.js';
 import { markPeerReset } from './federationReset.js';
 
@@ -103,3 +103,62 @@ export async function recoverOrDetectReset(
   await markPeerRecovered(peer.id);
   return 'recovered';
 }
+
+/**
+ * Detection-only epoch probe for peers already parked in `needs_attention`
+ * (design §4.1). Runs on the 15-minute health-check tick.
+ *
+ * The gap this closes: a reset peer can reach `needs_attention` via the
+ * AUTH-FAILURE path — its HTTP is up and returning 401/403 because the new
+ * incarnation has no peer row for us, so `consecutive_auth_failures` crosses
+ * `AUTH_FAILURE_THRESHOLD` — WITHOUT ever transitioning through `unreachable`.
+ * The `unreachable`-only recovery probe (`processRecoveryTick`) therefore never
+ * sees such a peer, so its epoch change is never observed and no
+ * `federation_reset_events` journal is ever created. A later manual admin
+ * Re-peer would then run `healResetIncarnation` with no journal row → no heal →
+ * the stale-friendship / split-DM split-brain persists for this sub-case. This
+ * pass probes those peers so the journal is created at detection time.
+ *
+ * **Detection only — never a recover-to-active.** Unlike `recoverOrDetectReset`,
+ * this NEVER flips a peer to `active`: a `needs_attention` peer's HMAC secret is
+ * desynced, so a matching or unknown epoch means "still broken, still needs an
+ * admin," not "recovered." On an observed epoch mismatch it calls
+ * `markPeerReset` (snapshot + journal + admin notify) and nothing else; the
+ * trusted baseline (`peer_instance_id`) and `hmac_secret` are left untouched.
+ * On a match / unknown / unreachable result it does nothing at all.
+ *
+ * Candidate set (deliberately small — one `/instance/info` GET per peer per
+ * tick): `status='needs_attention'` AND `peer_instance_id IS NOT NULL` (a null
+ * baseline has nothing to compare against) AND the reason is not already
+ * `peer_reset_detected` (those peers already carry a journal — re-probing would
+ * be wasted work). Peers whose reason is `auth_failures` or NULL qualify.
+ */
+export async function detectResetOnNeedsAttentionPeers(signal?: AbortSignal): Promise<void> {
+  const db = getDb();
+  const peers = db
+    .select({
+      id: schema.federationPeers.id,
+      origin: schema.federationPeers.origin,
+      peerInstanceId: schema.federationPeers.peerInstanceId,
+    })
+    .from(schema.federationPeers)
+    .where(and(
+      eq(schema.federationPeers.status, 'needs_attention'),
+      isNotNull(schema.federationPeers.peerInstanceId),
+      or(
+        isNull(schema.federationPeers.needsAttentionReason),
+        ne(schema.federationPeers.needsAttentionReason, 'peer_reset_detected'),
+      ),
+    ))
+    .all();
+
+  for (const peer of peers) {
+    const result = await probePeerReachable(peer.origin, signal);
+    // Detection fires ONLY on a reachable peer advertising a non-null epoch that
+    // differs from the trusted baseline. Everything else (unreachable, unknown
+    // epoch, or a matching epoch) is a no-op — no recover-to-active from here.
+    if (result.reachable && result.instanceId && peer.peerInstanceId && result.instanceId !== peer.peerInstanceId) {
+      markPeerReset(peer.id, peer.origin, peer.peerInstanceId, result.instanceId);
+    }
+  }
+}

packages/server/src/utils/federationWorker.ts

@@ -12,7 +12,7 @@ import { connectionManager } from '../ws/handler.js';
 import { generateThumbnail } from './thumbnail.js';
 import type { FederationRelayRequest, FederationRelayResponse, FederationRelayEvent } from '@backspace/shared';
 import { startupBootstrapSync, onPeerDeactivated } from './federationPeerActivation.js';
-import { probePeerReachable, recoverOrDetectReset } from './federationRecovery.js';
+import { probePeerReachable, recoverOrDetectReset, detectResetOnNeedsAttentionPeers } from './federationRecovery.js';
 import { backfillReplicatedProfileAssets } from '../routes/federation.js';
 import { invokePermanentFailureCallback } from './federationRollback.js';
 import { refreshPeerEpochs, getInstanceId } from './federationEpoch.js';
@@ -1180,6 +1180,17 @@ async function processHealthCheckTick(): Promise<void> {
   // relay/user activity. Best-effort — a failed fetch is a benign no-op retried
   // next tick, so it never disturbs the rest of the health-check work.
   await refreshPeerEpochs().catch(() => {});
+
+  // ── Reset detection for needs_attention peers (design §4.1) ─────────────────
+  // A reset peer can land in `needs_attention` via the auth-failure path (HTTP
+  // up, 401/403 from a new incarnation) WITHOUT ever passing through
+  // `unreachable`, so the unreachable-only recovery probe never observes its
+  // epoch change. Probe those peers here so a reset journal is created at
+  // detection time (otherwise a later manual Re-peer heals nothing). Detection
+  // ONLY — never flips a needs_attention peer to active. Best-effort: a failure
+  // is a benign no-op retried next tick and must not disturb the rest of the tick.
+  // No shared abort signal — probePeerReachable carries its own 10s timeout.
+  await detectResetOnNeedsAttentionPeers().catch(() => {});
 }
 
 // ─── Federated Call Health Sweep ────────────────────────────────────────────