sched: extract typed preparer/dispatcher seams; test impl out of production (F6)

src/wf_scheduling/recovery.py

@@ -171,16 +171,9 @@ def _mark_pending(run_store: Any, run_id: str) -> None:
 
 
 def _is_pending(run_store: Any, run_id: str) -> bool:
-    try:
-        return bool(run_store.is_pending_dispatch(run_id))
-    except AttributeError:
-        # Legacy stores without the pending protocol: treat as not pending.
-        return False
+    return bool(run_store.is_pending_dispatch(run_id))
 
 
 def clear_pending(run_store: Any, run_id: str) -> None:
     """Clear the pending-dispatch marker after the poll sweep dispatches."""
-    try:
-        run_store.clear_pending_dispatch(run_id)
-    except AttributeError:
-        return
+    run_store.clear_pending_dispatch(run_id)