sched: sibling-distinct lock identity; reject shared-store overlaps (R4 wave 4)

src/wf_scheduling/poll.py

@@ -31,7 +31,11 @@ from wf_scheduling.history import (
     HistoryRecorder,
 )
 from wf_scheduling.models import PendingCandidate
-from wf_scheduling.ownership import SchedulerOwnership, SecondOwnerError
+from wf_scheduling.ownership import (
+    SchedulerOwnership,
+    SecondOwnerError,
+    describe_unsupported_layout,
+)
 from wf_scheduling.prepare import InvocationPreparer, PreparationRejected
 
 UTC = timezone.utc
@@ -146,10 +150,12 @@ class Scheduler:
         or administering schedules would risk double admission.
         """
         ownership = self.ownership
-        if ownership is None or not ownership.covers(
-            getattr(self.schedule_store, "root", None),
-            getattr(self.run_store, "root", None),
-        ):
+        sched_root = getattr(self.schedule_store, "root", None)
+        runs_root = getattr(self.run_store, "root", None)
+        unsupported = describe_unsupported_layout(sched_root, runs_root)
+        if unsupported is not None:
+            raise SecondOwnerError(unsupported)
+        if ownership is None or not ownership.covers(sched_root, runs_root):
             raise SecondOwnerError(
                 "scheduler ownership must cover the schedule and run stores "
                 "before polling or mutating schedules"