refactor(cron): dedup EMFILE tick-failure handling; share the fd-exhaustion text matcher

/simplify-code findings on the salvage stack:
- the classify+reclaim+counter block was pasted verbatim into both ticker
  loops (_start and _start_multiplex) along with duplicated function-local
  imports — extracted _note_tick_failure() next to _backoff_wait_seconds
  so both loops share one implementation.
- hermes_cli/cron.py's EMFILE hint reimplemented the text half of
  _is_fd_exhaustion with a case-SENSITIVE variation (drift risk) — split
  _is_fd_exhaustion_text() out and use it from both.

11 EMFILE tests + 54 provider/ticker tests green; ruff clean.

cron/scheduler.py

@@ -1355,6 +1355,12 @@ def _is_lock_contention_errno(err: OSError) -> bool:
     return False
 
 
+def _is_fd_exhaustion_text(text: str) -> bool:
+    """Text-level half of :func:`_is_fd_exhaustion` (shared with the CLI hint)."""
+    lowered = text.lower()
+    return "too many open files" in lowered or "emfile" in lowered
+
+
 def _is_fd_exhaustion(exc: BaseException) -> bool:
     """Return True when *exc* indicates file-descriptor exhaustion.
 
@@ -1364,8 +1370,7 @@ def _is_fd_exhaustion(exc: BaseException) -> bool:
     """
     if isinstance(exc, OSError) and exc.errno in (errno.EMFILE, errno.ENFILE):
         return True
-    text = str(exc).lower()
-    return "too many open files" in text or "emfile" in text
+    return _is_fd_exhaustion_text(str(exc))
 
 
 def _reclaim_fds_best_effort() -> None:

cron/scheduler_provider.py

@@ -46,6 +46,24 @@ def _backoff_wait_seconds(interval: float, consecutive_failures: int) -> float:
     )
 
 
+def _note_tick_failure(exc: BaseException, consecutive_failures: int) -> int:
+    """Classify one failed tick and return the updated failure counter.
+
+    Shared by both ticker loops (#87644): on fd exhaustion, attempt
+    reclamation (gc.collect + raise the soft nofile limit) so the NEXT tick
+    can succeed, and bump the counter so ``_backoff_wait_seconds`` backs off
+    exponentially while the process has no chance of making progress.  Any
+    other failure resets the counter — backoff is reserved for the
+    self-inflicted EMFILE storm, not transient errors.
+    """
+    from cron.scheduler import _is_fd_exhaustion, _reclaim_fds_best_effort
+
+    if _is_fd_exhaustion(exc):
+        _reclaim_fds_best_effort()
+        return consecutive_failures + 1
+    return 0
+
+
 class CronScheduler(ABC):
     """Axis-B trigger provider. Decides WHEN a due cron job fires.
 
@@ -369,10 +387,6 @@ class InProcessCronScheduler(CronScheduler):
     ):
         import logging
         from cron.scheduler import tick as cron_tick
-        from cron.scheduler import (
-            _is_fd_exhaustion,
-            _reclaim_fds_best_effort,
-        )
         from cron.jobs import (
             clear_ticker_error,
             record_ticker_error,
@@ -446,16 +460,10 @@ class InProcessCronScheduler(CronScheduler):
                 # uid went unnoticed for ~14h with the reason buried in the
                 # gateway log (#68483).
                 record_ticker_error(f"{type(e).__name__}: {e}")
-                if _is_fd_exhaustion(e):
-                    # EMFILE: try to free descriptors (gc.collect + raise the
-                    # soft nofile limit) so the NEXT tick can succeed; back off
-                    # exponentially so the exhausted process stops hammering
-                    # the store while it has no chance of making progress
-                    # (#87644).
-                    _reclaim_fds_best_effort()
-                    consecutive_failures += 1
-                else:
-                    consecutive_failures = 0
+                # EMFILE: reclaim fds + back off exponentially so the
+                # exhausted process stops hammering the store while it has no
+                # chance of making progress (#87644).
+                consecutive_failures = _note_tick_failure(e, consecutive_failures)
             # Record liveness every iteration; bump the success marker only on a
             # clean tick, so status can tell "alive but failing every tick" from
             # "actually firing jobs" (#32612, #32895).
@@ -485,10 +493,6 @@ class InProcessCronScheduler(CronScheduler):
         """
         import logging
         from cron.scheduler import tick as cron_tick
-        from cron.scheduler import (
-            _is_fd_exhaustion,
-            _reclaim_fds_best_effort,
-        )
         from cron.jobs import (
             clear_ticker_error,
             record_ticker_error,
@@ -547,13 +551,8 @@ class InProcessCronScheduler(CronScheduler):
             except BaseException as e:
                 logger.error("Cron tick error: %s", e, exc_info=True)
                 _tick_error = f"{type(e).__name__}: {e}"
-                if _is_fd_exhaustion(e):
-                    # EMFILE: attempt fd reclamation so the next tick can
-                    # succeed, and back off exponentially (#87644).
-                    _reclaim_fds_best_effort()
-                    consecutive_failures += 1
-                else:
-                    consecutive_failures = 0
+                # EMFILE: reclaim fds + exponential backoff (#87644).
+                consecutive_failures = _note_tick_failure(e, consecutive_failures)
             else:
                 _tick_error = None
             # Record per-profile heartbeat after each tick cycle.

hermes_cli/cron.py

@@ -281,6 +281,7 @@ def cron_status():
             get_ticker_success_age,
             TICKER_INTERVAL_SECONDS,
         )
+        from cron.scheduler import _is_fd_exhaustion_text as _cron_is_fd_exhaustion_text
 
         # Allow ~3 missed ticker iterations (+ a little slack) before declaring
         # trouble. Derived from the shared interval constant so this threshold
@@ -323,7 +324,7 @@ def cron_status():
                         "gateway user, and prefer `docker exec -u <uid>:<gid>`.",
                         Colors.YELLOW,
                     ))
-                elif "Too many open files" in last_error or "EMFILE" in last_error:
+                elif _cron_is_fd_exhaustion_text(last_error):
                     print(color(
                         "  Hint: the ticker hit file-descriptor exhaustion "
                         "(EMFILE). The scheduler now retries with backoff and "