fix(embed): pin stdin to DEVNULL when spawning the daemon

hindsight-embed/hindsight_embed/daemon_embed_manager.py

@@ -147,7 +147,9 @@ def _detach_popen_kwargs(log_handle: IO[bytes]) -> dict:
     """Cross-platform kwargs to spawn a subprocess detached from the caller.
 
     On POSIX, `start_new_session=True` calls setsid(2) so the child
-    survives the parent's terminal. On Windows there is no setsid: we use
+    survives the parent's terminal; `stdin` is pinned to /dev/null so the
+    child never inherits a caller fd 0 that may be CLOEXEC (closed at exec,
+    leaving ``sys.stdin = None``). On Windows there is no setsid: we use
     `DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP`, which also means the
     child has no console, so stdin/stdout/stderr MUST be redirected or any
     write from the child crashes with "handle is invalid".
@@ -171,6 +173,7 @@ def _detach_popen_kwargs(log_handle: IO[bytes]) -> dict:
         }
     return {
         "start_new_session": True,
+        "stdin": subprocess.DEVNULL,
         "stdout": log_handle,
         "stderr": log_handle,
     }

hindsight-embed/tests/test_embed_manager.py

@@ -1,10 +1,12 @@
 """Tests for EmbedManager interface."""
 
+import io
+import subprocess
 from unittest.mock import MagicMock, patch
 
 from hindsight_embed import get_embed_manager
 from hindsight_embed._http_probe import ProbeResponse
-from hindsight_embed.daemon_embed_manager import DaemonEmbedManager
+from hindsight_embed.daemon_embed_manager import DaemonEmbedManager, _detach_popen_kwargs
 
 
 def _mock_sentence_transformers_present(monkeypatch):
@@ -684,3 +686,15 @@ def test_run_probe_still_reports_a_failed_command_as_none():
     import sys as _sys
 
     assert DaemonEmbedManager._run_probe([_sys.executable, "-c", "raise SystemExit(3)"]) is None
+
+
+def test_detach_popen_kwargs_pins_stdin():
+    """The daemon child must never inherit the caller's fd 0.
+
+    A caller can hold an fd 0 that is a socket opened with FD_CLOEXEC (e.g. a
+    TUI/gateway parent that wires its IPC channel onto fds 0-2). An inherited
+    fd 0 is closed by the kernel at exec, so the child would start with
+    ``sys.stdin = None`` and crash in ``_redirect_stdio_to_log()``.
+    """
+    kwargs = _detach_popen_kwargs(io.BytesIO())
+    assert kwargs["stdin"] == subprocess.DEVNULL