fix(gateway): contain output pump shutdown races

bot_bottle/gateway/bootstrap.py

@@ -136,10 +136,18 @@ def _pump(name: str, stream: IO[bytes]) -> None:
     """Read lines from `stream`, prefix with `[name]`, write to
     stdout. Runs in its own thread per child; daemon=True so a
     blocked read doesn't keep the process alive after main exits."""
-    for raw in iter(stream.readline, b""):
-        line = raw.decode("utf-8", errors="replace").rstrip("\n")
-        sys.stdout.write(f"[{name}] {line}\n")
-        sys.stdout.flush()
+    try:
+        for raw in iter(stream.readline, b""):
+            line = raw.decode("utf-8", errors="replace").rstrip("\n")
+            sys.stdout.write(f"[{name}] {line}\n")
+            sys.stdout.flush()
+    except (OSError, ValueError) as exc:
+        # The manager closes a dead child's pipe after wait() and before a
+        # restart. A pump can be between readline calls at that exact moment;
+        # closed-stream errors are normal completion, not uncaught thread
+        # failures. Preserve genuinely unexpected I/O diagnostics.
+        if not stream.closed:
+            _log(f"{name} output pump stopped: {type(exc).__name__}: {exc}")
 
 
 def _spawn(spec: _DaemonSpec) -> subprocess.Popen[bytes]:

tests/unit/test_gateway_init.py

@@ -23,6 +23,7 @@ from bot_bottle.gateway.bootstrap import (
     _DaemonManager,
     _argv_for_daemon,
     _env_for_daemon,
+    _pump,
     _selected_daemons,
 )
 from tests._bin import SLEEP
@@ -565,5 +566,26 @@ class TestMainEndToEnd(unittest.TestCase):
         self.assertIn("no daemons selected", out)
 
 
+class _FailingStream:
+    def __init__(self, *, closed: bool) -> None:
+        self.closed = closed
+
+    def readline(self) -> bytes:
+        raise ValueError("I/O operation on closed file")
+
+
+class TestOutputPump(unittest.TestCase):
+    def test_closed_stream_race_is_normal_completion(self) -> None:
+        with patch("bot_bottle.gateway.bootstrap._log") as log:
+            _pump("egress", _FailingStream(closed=True))  # type: ignore[arg-type]
+        log.assert_not_called()
+
+    def test_unexpected_io_failure_is_logged(self) -> None:
+        with patch("bot_bottle.gateway.bootstrap._log") as log:
+            _pump("egress", _FailingStream(closed=False))  # type: ignore[arg-type]
+        log.assert_called_once()
+        self.assertIn("output pump stopped", log.call_args.args[0])
+
+
 if __name__ == "__main__":
     unittest.main()