diff --git a/packages/owletto b/packages/owletto
index 6e7243ffa..887e8626a 160000
--- a/packages/owletto
+++ b/packages/owletto
@@ -1 +1 @@
-Subproject commit 6e7243ffa1262876430755f3405423995d937eb5
+Subproject commit 887e8626a194da652bde66772c3cf6dfeb704820
diff --git a/packages/server/src/__tests__/integration/watchers/automation-contract.test.ts b/packages/server/src/__tests__/integration/watchers/automation-contract.test.ts
index 8896c1df8..9cc8a68b8 100644
--- a/packages/server/src/__tests__/integration/watchers/automation-contract.test.ts
+++ b/packages/server/src/__tests__/integration/watchers/automation-contract.test.ts
@@ -17,6 +17,7 @@ import { computePendingWindow } from '../../../utils/window-utils';
 import {
   dispatchPendingWatcherRuns,
   materializeDueWatcherRuns,
+  sweepStaleWatcherRuns,
 } from '../../../watchers/automation';
 import { generateSecureToken, hashToken } from '../../../auth/oauth/utils';
 import { cleanupTestDatabase, getTestDb } from '../../setup/test-db';
@@ -1043,4 +1044,98 @@ describe('watcher automation contract', () => {
       expect(secondNextRunMs).toBe(firstNextRunMs);
     });
   });
+
+  describe('sweepStaleWatcherRuns liveness reaping', () => {
+    // Seed a `running` watcher run with controlled claim/heartbeat ages.
+    // Omitting `heartbeatAgo` mirrors a client that never heartbeats — the
+    // claim sets last_heartbeat_at == claimed_at, so the row must fall to the
+    // coarse 2h path, never the fast heartbeat path.
+    async function seedRunningWatcherRun(opts: {
+      claimedAgo: string;
+      heartbeatAgo?: string;
+    }) {
+      const { sql, dbClient, workspace, watcherId, agent } = await createAutomatedWatcher();
+      const granularity = inferWatcherGranularityFromSchedule('0 9 * * *');
+      const { windowStart, windowEnd } = await computePendingWindow(
+        dbClient,
+        watcherId,
+        granularity
+      );
+      const queued = await createWatcherRun({
+        organizationId: workspace.org.id,
+        watcherId,
+        agentId: agent.agentId,
+        windowStart: windowStart.toISOString(),
+        windowEnd: windowEnd.toISOString(),
+        dispatchSource: 'scheduled',
+        deviceWorkerId: '11111111-1111-1111-1111-111111111111',
+        agentKind: 'claude-code',
+      });
+      const heartbeatAgo = opts.heartbeatAgo ?? opts.claimedAgo;
+      await sql`
+        UPDATE runs
+        SET status = 'running',
+            claimed_by = 'mac-sweep-test',
+            claimed_at = NOW() - ${opts.claimedAgo}::interval,
+            last_heartbeat_at = NOW() - ${heartbeatAgo}::interval
+        WHERE id = ${queued.runId}
+      `;
+      return { sql, runId: queued.runId };
+    }
+
+    it('reaps a heartbeating run that went silent past the heartbeat window', async () => {
+      // Beat once after claim (10m ago > claim 1h ago), then silent >3min.
+      const { sql, runId } = await seedRunningWatcherRun({
+        claimedAgo: '1 hour',
+        heartbeatAgo: '10 minutes',
+      });
+      const { timedOut } = await sweepStaleWatcherRuns(sql);
+      expect(timedOut).toBeGreaterThanOrEqual(1);
+      const [row] = await sql`SELECT status, error_message FROM runs WHERE id = ${runId}`;
+      expect(String(row.status)).toBe('timeout');
+      expect(String(row.error_message ?? '')).toMatch(/heartbeat went silent/i);
+    });
+
+    it('leaves a run with a fresh heartbeat running', async () => {
+      const { sql, runId } = await seedRunningWatcherRun({
+        claimedAgo: '1 hour',
+        heartbeatAgo: '30 seconds',
+      });
+      await sweepStaleWatcherRuns(sql);
+      const [row] = await sql`SELECT status FROM runs WHERE id = ${runId}`;
+      expect(String(row.status)).toBe('running');
+    });
+
+    it('does not coarse-reap a live heartbeating run older than the 2h TTL', async () => {
+      // Claimed 3h ago but heartbeating fresh (30s) → still alive. The coarse
+      // 2h backstop must NOT touch it; only the (un-lapsed) fast path governs
+      // a heartbeating run. Guards against killing a legitimately long turn.
+      const { sql, runId } = await seedRunningWatcherRun({
+        claimedAgo: '3 hours',
+        heartbeatAgo: '30 seconds',
+      });
+      await sweepStaleWatcherRuns(sql);
+      const [row] = await sql`SELECT status FROM runs WHERE id = ${runId}`;
+      expect(String(row.status)).toBe('running');
+    });
+
+    it('does not fast-reap a recent run that never heartbeats', async () => {
+      // last_heartbeat_at == claimed_at (no beat) + only 30m old → the fast
+      // path must NOT fire; it stays running until the 2h coarse backstop.
+      // Backward-compat guard for clients that do not heartbeat.
+      const { sql, runId } = await seedRunningWatcherRun({ claimedAgo: '30 minutes' });
+      await sweepStaleWatcherRuns(sql);
+      const [row] = await sql`SELECT status FROM runs WHERE id = ${runId}`;
+      expect(String(row.status)).toBe('running');
+    });
+
+    it('reaps a non-heartbeating run via the coarse 2h backstop', async () => {
+      const { sql, runId } = await seedRunningWatcherRun({ claimedAgo: '3 hours' });
+      const { timedOut } = await sweepStaleWatcherRuns(sql);
+      expect(timedOut).toBeGreaterThanOrEqual(1);
+      const [row] = await sql`SELECT status, error_message FROM runs WHERE id = ${runId}`;
+      expect(String(row.status)).toBe('timeout');
+      expect(String(row.error_message ?? '')).toMatch(/2 hours/i);
+    });
+  });
 });
diff --git a/packages/server/src/watchers/automation.ts b/packages/server/src/watchers/automation.ts
index df759547d..5b357e496 100644
--- a/packages/server/src/watchers/automation.ts
+++ b/packages/server/src/watchers/automation.ts
@@ -406,34 +406,76 @@ export async function reconcileWatcherRuns(db?: DbClient): Promise<ReconcileWatc
 }
 
 /**
- * Coarse backstop for watcher runs that never reached terminal state.
+ * Backstop for watcher runs that never reached terminal state.
  *
  * The primary lifecycle is driven by WatcherRunTracker (in-process completion
- * events) plus startup reconciliation on gateway boot. This sweeper only
- * catches truly stuck runs — the tracker entry was lost without a crash
- * (graceful shutdown mid-turn, queue message silently dropped, etc). TTL is
- * intentionally generous so long LLM turns are not killed.
+ * events) plus startup reconciliation on gateway boot. This sweeper catches
+ * stuck runs — the tracker entry was lost without a clean completion (graceful
+ * shutdown mid-turn, queue message silently dropped, the device executor
+ * crashing or its process being abandoned, etc).
+ *
+ * Two reap paths, both keyed on the run's OWN liveness so they're correct
+ * under N replicas (a run actively executing anywhere keeps its heartbeat
+ * fresh, so no replica's sweep touches it):
+ *
+ *  1. Heartbeat-stale (fast, ~minutes): a run whose executor heartbeats —
+ *     the device WatcherDispatcher beats every {@link WATCHER_HEARTBEAT_MS}ms
+ *     during the turn — and has gone silent past the window. We require
+ *     `last_heartbeat_at > claimed_at` (i.e. it beat at least once after being
+ *     claimed) so this NEVER fires for a client that doesn't heartbeat: the
+ *     claim sets `last_heartbeat_at == claimed_at`, so a non-heartbeating run
+ *     stays equal and falls through to the coarse path. Fully backward
+ *     compatible with older Mac apps.
+ *  2. Coarse TTL (generous, 2h): the legacy backstop for runs that never
+ *     heartbeat — measured from the claim/creation. Kept so a long but live
+ *     non-heartbeating turn isn't killed prematurely.
  */
 const WATCHER_RUN_STALE_INTERVAL = '2 hours';
 
+/** ~4 missed 30s device heartbeats. A heartbeating executor that goes silent
+ *  this long is crashed/abandoned; a live one (beats every ~30s) never lapses. */
+const WATCHER_RUN_HEARTBEAT_STALE_INTERVAL = '3 minutes';
+
 export async function sweepStaleWatcherRuns(
   db?: DbClient
 ): Promise<{ timedOut: number }> {
   const sql = db ?? getDb();
-  const errorMessage = `Watcher run exceeded ${WATCHER_RUN_STALE_INTERVAL} without reaching terminal state`;
+  const heartbeatError = `Watcher run heartbeat went silent for over ${WATCHER_RUN_HEARTBEAT_STALE_INTERVAL} — the executor crashed or was abandoned`;
+  const coarseError = `Watcher run exceeded ${WATCHER_RUN_STALE_INTERVAL} without reaching terminal state`;
   const result = await sql`
     UPDATE runs
     SET status = 'timeout',
         completed_at = current_timestamp,
-        error_message = ${errorMessage}
+        error_message = CASE
+          WHEN last_heartbeat_at IS NOT NULL
+               AND claimed_at IS NOT NULL
+               AND last_heartbeat_at > claimed_at
+            THEN ${heartbeatError}
+          ELSE ${coarseError}
+        END
     WHERE run_type = 'watcher'
       AND status IN ('running', 'claimed')
-      AND COALESCE(claimed_at, created_at)
-          < current_timestamp - ${WATCHER_RUN_STALE_INTERVAL}::interval
+      AND (
+        -- Fast path: the executor was heartbeating, then went silent.
+        (last_heartbeat_at IS NOT NULL
+         AND claimed_at IS NOT NULL
+         AND last_heartbeat_at > claimed_at
+         AND last_heartbeat_at
+             < current_timestamp - ${WATCHER_RUN_HEARTBEAT_STALE_INTERVAL}::interval)
+        OR
+        -- Coarse backstop: ONLY for runs that never heartbeated. A heartbeating
+        -- run is governed solely by the fast path above — so a live one that
+        -- legitimately runs past 2h (fresh heartbeat) is never killed here.
+        ((last_heartbeat_at IS NULL
+          OR claimed_at IS NULL
+          OR last_heartbeat_at <= claimed_at)
+         AND COALESCE(claimed_at, created_at)
+             < current_timestamp - ${WATCHER_RUN_STALE_INTERVAL}::interval)
+      )
   `;
   const timedOut = Number(result.count ?? 0);
   if (timedOut > 0) {
-    logger.warn({ timedOut }, '[watchers] Swept stale watcher runs past coarse TTL');
+    logger.warn({ timedOut }, '[watchers] Swept stale watcher runs');
   }
   return { timedOut };
 }