sched: gate scheduled resumes on the shared execution slot, with drain tracking (B2)

src/wf_scheduling/poll.py

@@ -190,11 +190,19 @@ class Scheduler:
         return admission.schedule_id
 
     def _task_load(self) -> int:
-        from wf_scheduling.recovery import _is_pending
+        from wf_scheduling.recovery import _is_pending, is_executing
 
         count = 0
         for run in self.run_store.list_runs():
             if self._status_value(run) != "admitted":
+                # A mid-resume scheduled run is interrupted but holds the
+                # durable executing mark: it occupies a live execution
+                # slot exactly like a dispatched run (B2), so the shared
+                # capacity gate must count it.
+                if is_executing(self.run_store, run.id) and not _is_pending(
+                    self.run_store, run.id
+                ):
+                    count += 1
                 continue
             if _is_pending(self.run_store, run.id):
                 continue