- _write_machine_sentinel_line: wrap the print() fallback so a closed
redirected stream (ValueError, not OSError) can't propagate out of the
ready path and kill a healthy serve; document that pythonw port
discovery relies on the HERMES_DESKTOP_READY_FILE channel, not stdout
- regression test: stderr=DEVNULL instead of PIPE — with the stdout
redirect active all server logging lands on stderr, and an unread
stderr pipe can fill and block the child before the sentinel, flaking
the test at the 120s timeout
Since 6d4e851d8 the serve startup path imports tui_gateway.server (for the
flush-on-SIGTERM handlers) before the READY sentinel is printed. That module
redirects sys.stdout to sys.stderr at import time, so the
HERMES_(BACKEND|DASHBOARD)_READY port=<n> sentinel landed on stderr while the
Electron desktop spawn watches child.stdout only — the desktop timed out
after 90s and killed a perfectly healthy backend (issue #96282).
Write the sentinel to the real stdout file descriptor (fd 1 is untouched by
the Python-level redirect), with a print() fallback.
Adds a regression test that captures stdout/stderr separately — the existing
E2E suite merges them, which is exactly how this slipped past CI.
A held port made 'hermes serve' print only uvicorn's bare
'ERROR: [Errno 98/10048] error while attempting to bind on address'
and exit 1 — indistinguishable from a broken backend for the desktop
spawn and wrapping scripts.
- Preflight bind probe (matching uvicorn's SO_REUSEADDR bind flags)
before uvicorn.Server; on conflict print machine-readable
'BACKEND_PORT_IN_USE port=<port>' + a human hint naming likely
holders, exit 75 (EX_TEMPFAIL — existing repo convention, see
gateway/restart.py, kanban_db.py).
- Probe-to-bind race covered: SystemExit(1) from uvicorn's own bind
failure is re-checked and translated on both POSIX and Windows
runner paths.
- --port 0 (ephemeral) short-circuits the probe: unchanged behavior.
- HERMES_BACKEND_READY contract untouched.
- Tests: real held-socket repro (sentinel + exit 75, sabotage-proven
to fail as bare exit 1 without the fix), free-port boot regression,
ephemeral-port regression, probe/classification units.
- Docs: port-conflict paragraph under 'hermes serve' in
reference/cli-commands.md.
kshitijk4poor