fix(kanban): fingerprint crash errors to prevent fleet-wide retry exhaustion

When a systemic failure (provider outage, auth expiry, OOM) crashes
multiple workers simultaneously, detect_crashed_workers increments
each task failure counter independently. The circuit breaker only
trips after N × failure_limit retries across the fleet.

Fingerprint crash errors by normalizing host-specific details (PIDs,
timestamps). When 3+ tasks crash with the same fingerprint in a
single detection cycle, immediately trip the circuit breaker
(failure_limit=1) instead of waiting for repeated failures.

Isolated crashes (unique fingerprints) retain their normal retry
budget. Protocol violations continue to trip immediately.

Includes regression tests for systemic and isolated crash paths.

hermes_cli/kanban_db.py

@@ -3684,18 +3684,29 @@ def detect_crashed_workers(conn: sqlite3.Connection) -> list[str]:
     # human with a clear reason than to loop ``DEFAULT_FAILURE_LIMIT``
     # times first.
     auto_blocked: list[str] = []
-    for tid, pid, claimer, protocol_violation, error_text in crash_details:
-        tripped = _record_task_failure(
-            conn, tid,
-            error=error_text,
-            outcome="crashed",
-            failure_limit=(1 if protocol_violation else None),
-            release_claim=False,
-            end_run=False,
-            event_payload_extra={"pid": pid, "claimer": claimer},
-        )
-        if tripped:
-            auto_blocked.append(tid)
+    if crash_details:
+        # Fingerprint errors to detect systemic failures.
+        _fp_counts: dict[str, int] = {}
+        for _, _, _, _, err_text in crash_details:
+            fp = _error_fingerprint(err_text)
+            _fp_counts[fp] = _fp_counts.get(fp, 0) + 1
+        for tid, pid, claimer, protocol_violation, error_text in crash_details:
+            fp = _error_fingerprint(error_text)
+            is_systemic = (
+                not protocol_violation
+                and _fp_counts.get(fp, 0) >= 3
+            )
+            tripped = _record_task_failure(
+                conn, tid,
+                error=error_text,
+                outcome="crashed",
+                failure_limit=1 if (protocol_violation or is_systemic) else None,
+                release_claim=False,
+                end_run=False,
+                event_payload_extra={"pid": pid, "claimer": claimer},
+            )
+            if tripped:
+                auto_blocked.append(tid)
     # Stash auto-blocked ids on the function for the dispatch loop to pick up.
     # Keeps the public return type (``list[str]``) stable for direct callers
     # and tests that destructure the result; ``dispatch_once`` reads this