pause_intake answers False when claimed work outlasts its timeout, and reload then resumes intake and raises RebuildBusy before tearing anything down

backend/tests/flow/test_engine_hold.py

@@ -5,13 +5,14 @@ service stops claiming and its timers once claimed work has finished. Both
 wait without a limit and can be aborted.
 """
 
+import asyncio
 import threading
 import time
 
 import pytest
 
 from fluksio.flow import executor
-from fluksio.flow.controller import FlowController, LoadedNode
+from fluksio.flow.controller import FlowController, LoadedNode, RebuildBusy
 from fluksio.flow.executor import ExecutionService
 from fluksio.flow.messages import DType, MessageSpec
 from fluksio.flow.namespace import Rename
@@ -149,6 +150,29 @@ def test_pause_intake_waits_out_a_claim_already_under_way(monkeypatch):
         service.stop()
 
 
+def test_a_reload_that_cannot_drain_leaves_the_pipeline_as_it_was(
+    tmp_path, monkeypatch
+):
+    monkeypatch.setattr(executor, "DRAIN_TIMEOUT_S", 0.05)
+    seen: list = []
+    running, finish, consume = _blocking(seen)
+    pipeline, service, source = _engine(consume)
+    controller = FlowController(FlowStore(tmp_path / "flows"), execution=service)
+    controller.pipeline = pipeline
+    service.start()
+    try:
+        source.inject({"reading": 1.0})
+        assert running.wait(5)
+        with pytest.raises(RebuildBusy):
+            asyncio.run(controller.reload())
+        assert controller.pipeline is pipeline
+        assert service._pipeline is pipeline
+        assert service._intake.is_set()
+    finally:
+        finish.set()
+        service.stop()
+
+
 def test_a_hold_waits_out_a_claim_already_under_way():
     seen: list = []
     queue = SlowClaim()