diff --git a/cron/jobs.py b/cron/jobs.py
index 044d0bee54ecf..9df4eb7dfdbb4 100644
--- a/cron/jobs.py
+++ b/cron/jobs.py
@@ -886,6 +886,9 @@ def _classify_dispatch_lateness(lateness_seconds: float, grace_seconds: int) ->
 _persisted_error_recoveries: int = 0
 # Bounded in-memory history kept by every probe-visible fire-path counter.
 _TELEMETRY_RECENT_HISTORY = 20
+# A fire_claim younger than this is treated as a live run in another process
+# (heartbeat cadence is 60 s; matches the claim TTL used by claim_job_fire).
+_STALE_ERROR_FIRE_CLAIM_TTL_SECONDS = 300.0
 _persisted_error_recoveries_recent: list = []
 
 
@@ -906,6 +909,15 @@ def _job_is_stale_error_recurring(
         return False
     if _job_running_in_this_process(str(job.get("id") or "")):
         return False
+    # Cross-process liveness (2026-09-02 brain incident): a run owned by
+    # ANOTHER scheduler process sharing this jobs store (e.g. several Desktop
+    # profile tabs + the gateway) heartbeats ``fire_claim`` every
+    # _RUN_CLAIM_HEARTBEAT_SECONDS. While that claim is fresh the job is not
+    # wedged — it is running elsewhere — and re-arming it here makes every
+    # other ticker claim-fight the live run (171 re-arms, ~175 junk
+    # "Fire claim lost" execution rows, then the live run was killed).
+    if _claim_is_live(job.get("fire_claim"), now, _STALE_ERROR_FIRE_CLAIM_TTL_SECONDS):
+        return False
     last_run = job.get("last_run_at")
     last_run_dt = _parse_aware(last_run) if last_run else None
     if last_run_dt is None:
diff --git a/tests/cron/test_recurring_persisted_error_recovery.py b/tests/cron/test_recurring_persisted_error_recovery.py
index 50b86673fe8ea..535ef65a9855b 100644
--- a/tests/cron/test_recurring_persisted_error_recovery.py
+++ b/tests/cron/test_recurring_persisted_error_recovery.py
@@ -161,3 +161,33 @@ def test_recent_error_within_cadence_not_force_rearmed(self, cron_env, monkeypat
             "a within-cadence error is a normal retry — must not be "
             "force-re-armed onto an immediate fire"
         )
+
+    def test_live_fire_claim_from_other_process_not_rearmed(self, cron_env, monkeypatch):
+        """A stale-error job whose ``fire_claim`` is being heartbeated by a run
+        in ANOTHER process is running, not wedged. Re-arming it would make this
+        ticker claim-fight the live run (2026-09-02 multi-Desktop-tab incident:
+        171 re-arms, ~175 junk executions, live run killed)."""
+        S, E, J, env = _setup(cron_env, monkeypatch)
+        job_id = env["job_id"]
+
+        _persist_stale_error(J, job_id, error_age_minutes=110)
+        now = datetime.now(timezone.utc)
+        J.update_job(
+            job_id,
+            {"fire_claim": {"at": now.isoformat(), "by": "other-host:deadbeef"}},
+        )
+
+        job = J.get_job(job_id)
+        assert not J._job_is_stale_error_recurring(job, job["schedule"], now)
+
+        with mock.patch("cron.jobs.load_jobs", return_value=[job]):
+            S.tick(verbose=False, sync=True)
+        assert E.latest_execution(job_id) is None, (
+            "a job with a live fire_claim held by another process must not be "
+            "re-armed by stale-error recovery"
+        )
+
+        # Once the foreign claim has expired (owner died), recovery resumes.
+        expired = (now - timedelta(seconds=J._STALE_ERROR_FIRE_CLAIM_TTL_SECONDS + 1)).isoformat()
+        J.update_job(job_id, {"fire_claim": {"at": expired, "by": "other-host:deadbeef"}})
+        assert J._job_is_stale_error_recurring(J.get_job(job_id), job["schedule"], now)