fix(ansible): a run that waited says so in its stored output, not only live (#5158)

The "[queued — waiting for run X on the same host]" and run-slot lines were
broadcast to live viewers and never stored, so a run that sat queued had no
record of why once the live view was gone (CI 8439: the overlap test found
the order right and the explanation missing). _claim_hosts now returns the
line it waited on and start_run seeds the run's output with every wait.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/test_ansible_overlap.py

@@ -47,18 +47,18 @@ def test_a_second_run_on_the_same_host_waits_for_the_first(gate):
     app = gate.app
 
     async def go():
-        assert await executor._claim_hosts(app, "a", {"web"}) is False
+        assert await executor._claim_hosts(app, "a", {"web"}) is None
         b = asyncio.create_task(executor._claim_hosts(app, "b", {"web", "db"}))
         await asyncio.sleep(0.05)
         assert not b.done()
         held = app._ansible_host_gate["held"]
         assert "db" not in held                 # all or nothing: b holds no half
-        assert await executor._claim_hosts(app, "c", {"db"}) is False
+        assert await executor._claim_hosts(app, "c", {"db"}) is None
         executor._release_hosts(app, "c", {"db"})
         await asyncio.sleep(0.05)
         assert not b.done()                     # web is still a's
         executor._release_hosts(app, "a", {"web"})
-        assert await asyncio.wait_for(b, 5) is True
+        assert "waiting for run a" in await asyncio.wait_for(b, 5)
         assert held == {"web": "b", "db": "b"}
 
     asyncio.run(go())