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fix(gateway): use git HEAD SHA, not file mtimes, for stale-code check (#19740)

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The stale-code self-check (Issue #17648) used sentinel-file mtimes to
decide whether the gateway survived a `hermes update` with stale
`sys.modules`. That signal false-positives on any write to the
sentinel files — including agent-driven edits during Hermes-on-Hermes
dev sessions. Telling the agent to patch `run_agent.py` would flip
the check to True on the next user message and force a gateway
restart even though no update happened.

Switch the signal to `git rev-parse HEAD`. Agent file edits don't
move HEAD; `hermes update` (git pull) always does. Reading .git/HEAD
directly (no subprocess) with a 5s cache keeps the overhead negligible
on bursty chats. Non-git installs short-circuit to False — the
stale-modules class can't occur without a git-backed update path, so
there's nothing to detect.

The legacy `_compute_repo_mtime` helper is kept but unused by
detection, reserved as a fallback hook for future pip-install update
paths.

- _read_git_head_sha(): resolves HEAD across main checkout, worktree
  (follows `gitdir:` + `commondir` pointers), and packed-refs layouts.
- _current_git_sha_cached(): per-runner 5s SHA cache.
- _detect_stale_code(): boot SHA vs current SHA, returns False when
  either is unavailable.
- Tests cover all four layouts, the agent-edits-don't-trigger
  regression, and cache behavior.

Refs #17648.
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Teknium 2026-05-04 12:33:21 -07:00 • committed by GitHub
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gateway/run.py
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@ -101,10 +101,21 @@ _AUTO_CONTINUE_FRESHNESS_SECS_DEFAULT = 60 * 60
# already-loaded stale module object and raises ``ImportError`` — see
# Issue #17648. Rather than papering over the import failure site-by-site
# in every tool file, detect the stale state centrally and auto-restart
# so the gateway reloads with fresh code. The sentinel files below are
# the canonical repo-level markers that every update touches; if any is
# newer than the gateway's boot time, we know the running process is out
# of date.
# so the gateway reloads with fresh code.
#
# The signal we use is ``git rev-parse HEAD`` — the only thing ``hermes
# update`` moves that is NOT moved by agent-driven file edits. Earlier
# revisions of this check compared file mtimes across a sentinel set
# (run_agent.py, gateway/run.py, ...), but that produced false positives
# whenever the agent edited its own source files during a session:
# mtime jumps, stale-check fires, gateway restarts, user must retype.
# See the conversation at PR #<this> for the motivating incident.
#
# The legacy mtime sentinels are kept ONLY as a last-resort fallback for
# non-git installs (pip install from wheel, sparse clones with no .git
# dir). In those environments ``hermes update`` is not a supported path,
# so the check effectively no-ops — which is the safe behavior: better
# to ship one broken import than to restart on every agent-edit.
_STALE_CODE_SENTINELS: tuple[str, ...] = (
"hermes_cli/config.py",
"hermes_cli/__init__.py",
@ -113,10 +124,106 @@ _STALE_CODE_SENTINELS: tuple[str, ...] = (
"pyproject.toml",
)
# Cache git HEAD reads across consecutive messages so a chat burst doesn't
# spawn one subprocess per message. 5s is long enough to collapse a burst
# and short enough that the real post-update detection still fires within
# the user's perceived "next message" window.
_GIT_SHA_CACHE_TTL_SECS = 5.0
def _read_git_head_sha(repo_root: Path) -> Optional[str]:
"""Return the git HEAD SHA for ``repo_root``, or None if unavailable.
Reads ``.git/HEAD`` directly (and follows one level of ref) instead
of shelling out to ``git`` — cheaper, no subprocess tax, works on
gateway hosts that don't have a ``git`` binary on PATH. Returns
None for non-git installs (no ``.git`` dir) or any I/O error; callers
treat None as "can't tell" and skip the check.
Supports the three layouts we care about:
1. Main checkout: ``<repo>/.git/`` is a directory.
2. Git worktree: ``<repo>/.git`` is a file ``gitdir: <path>`` that
points at ``<main>/.git/worktrees/<name>/``. The worktree's
gitdir has HEAD + index but NOT refs/heads/ — those live in
the main checkout, and ``<worktree-gitdir>/commondir`` points
at the main ``.git``. We search both locations for refs.
3. Packed refs: ``refs/heads/<branch>`` is absent on disk but
listed in ``<main-git-dir>/packed-refs``.
"""
try:
git_dir = repo_root / ".git"
# Worktrees store ``.git`` as a file pointing at gitdir: <path>
if git_dir.is_file():
try:
content = git_dir.read_text().strip()
if content.startswith("gitdir:"):
git_dir = Path(content.split(":", 1)[1].strip())
if not git_dir.is_absolute():
git_dir = (repo_root / git_dir).resolve()
except OSError:
return None
if not git_dir.is_dir():
return None
# Figure out the "common" git dir — the one that owns shared refs.
# For a worktree, commondir points at it (relative path, resolve
# against git_dir). For a main checkout, common_dir == git_dir.
common_dir = git_dir
commondir_file = git_dir / "commondir"
if commondir_file.is_file():
try:
rel = commondir_file.read_text().strip()
candidate = (git_dir / rel).resolve() if rel else git_dir
if candidate.is_dir():
common_dir = candidate
except OSError:
pass
head_path = git_dir / "HEAD"
if not head_path.is_file():
return None
head_content = head_path.read_text().strip()
if head_content.startswith("ref:"):
# Symbolic ref — follow one level (e.g. ref: refs/heads/main).
# Worktree-local refs (bisect, rebase-merge state) live under
# git_dir; shared refs (refs/heads/*, refs/tags/*) live under
# common_dir. Try git_dir first, then common_dir.
ref_rel = head_content.split(":", 1)[1].strip()
for base in (git_dir, common_dir) if git_dir != common_dir else (git_dir,):
ref_path = base / ref_rel
if ref_path.is_file():
try:
sha = ref_path.read_text().strip()
except OSError:
continue
if sha:
return sha
# Packed refs fallback — always stored in the common dir.
packed = common_dir / "packed-refs"
if packed.is_file():
try:
for line in packed.read_text().splitlines():
line = line.strip()
if not line or line.startswith("#") or line.startswith("^"):
continue
parts = line.split(None, 1)
if len(parts) == 2 and parts[1] == ref_rel:
return parts[0] or None
except OSError:
return None
return None
# Detached HEAD — content is the SHA directly.
return head_content or None
except Exception:
return None
def _compute_repo_mtime(repo_root: Path) -> float:
"""Return the newest mtime across the stale-code sentinel files.
Legacy fallback used only for non-git installs (``.git`` missing).
Missing files are ignored (they may not exist on older checkouts).
Returns 0.0 if no sentinel file is readable — treat that as "can't
tell", which downstream callers interpret as "not stale" to avoid
@ -1005,6 +1112,7 @@ class GatewayRunner:
# running __init__ don't crash when _handle_message reads these.
_boot_wall_time: float = 0.0
_boot_repo_mtime: float = 0.0
_boot_git_sha: Optional[str] = None
_stale_code_restart_triggered: bool = False
def __init__(self, config: Optional[GatewayConfig] = None):
@ -1020,15 +1128,23 @@ class GatewayRunner:
try:
self._boot_wall_time: float = time.time()
self._repo_root_for_staleness: Path = Path(__file__).resolve().parent.parent
self._boot_git_sha: Optional[str] = _read_git_head_sha(
self._repo_root_for_staleness,
)
self._boot_repo_mtime: float = _compute_repo_mtime(
self._repo_root_for_staleness,
)
except Exception:
self._boot_wall_time = 0.0
self._repo_root_for_staleness = Path(".")
self._boot_git_sha = None
self._boot_repo_mtime = 0.0
self._stale_code_notified: set[str] = set()
self._stale_code_restart_triggered: bool = False
# Cached current-SHA read, refreshed at most every
# _GIT_SHA_CACHE_TTL_SECS so bursty chats don't hammer the filesystem.
self._cached_current_sha: Optional[str] = self._boot_git_sha
self._cached_current_sha_at: float = self._boot_wall_time
# Load ephemeral config from config.yaml / env vars.
# Both are injected at API-call time only and never persisted.
@ -2737,36 +2853,69 @@ class GatewayRunner:
task.add_done_callback(self._background_tasks.discard)
return True
def _current_git_sha_cached(self) -> Optional[str]:
"""Return the current HEAD SHA, cached for _GIT_SHA_CACHE_TTL_SECS.
A bursty chat (user mashes "hello?" three times) would otherwise
re-read ``.git/HEAD`` on every message. Caching collapses that
into a single read and still re-checks within the user's
perceived "next message" window.
"""
now = time.time()
if (
self._cached_current_sha is not None
and (now - self._cached_current_sha_at) < _GIT_SHA_CACHE_TTL_SECS
):
return self._cached_current_sha
try:
sha = _read_git_head_sha(self._repo_root_for_staleness)
except Exception:
sha = None
self._cached_current_sha = sha
self._cached_current_sha_at = now
return sha
def _detect_stale_code(self) -> bool:
"""Return True if source files on disk are newer than the running process.
"""Return True if the git HEAD moved since this process booted.
A gateway that survives ``hermes update`` (manual SIGTERM never
escalated, systemd restart race, detached-process respawn failed,
etc.) keeps pre-update modules cached in ``sys.modules``. Later
imports of names added post-update — e.g. ``cfg_get`` from PR
#17304 — raise ImportError against the stale module object (see
Issue #17648). Detecting this at the source — "the code on disk
is newer than me" — lets us auto-restart instead of serving
broken responses until the user notices and runs
``hermes gateway restart`` manually.
Issue #17648).
Returns False when the boot-time snapshot is unavailable or no
sentinel file is readable, to avoid false-positive restart loops
in unusual checkouts (sparse clones, read-only filesystems).
We compare the git HEAD SHA at boot to the current SHA on disk.
``hermes update`` always moves HEAD forward via ``git pull``;
agent file edits (the agent patching ``run_agent.py`` or
``gateway/run.py`` during a self-dev session) never move HEAD.
That makes SHA comparison free of the false-positive class that
the old mtime check suffered from — the agent can edit any file
without triggering a phantom restart.
Returns False when:
- the boot SHA is unavailable (non-git install, first call
during partial init, etc.); we can't tell and refuse to loop
- the current SHA matches the boot SHA
- reading the current SHA fails for any reason
"""
if not self._boot_wall_time or not self._boot_repo_mtime:
if not self._boot_wall_time:
return False
if not self._boot_git_sha:
# Non-git install. ``hermes update`` is git-based, so a
# non-git install can't experience the stale-modules class
# this check exists to catch. Return False — no check, no
# false positives. (If we ever ship a pip-install update
# path, we'd add a persistent update marker here and compare
# its timestamp to self._boot_wall_time.)
return False
try:
current = _compute_repo_mtime(self._repo_root_for_staleness)
current = self._current_git_sha_cached()
except Exception:
return False
if current <= 0.0:
if not current:
return False
# 2-second slack guards against filesystems with coarse mtime
# resolution (FAT32, some NFS mounts). Real updates always move
# the newest-file mtime forward by minutes, so this doesn't hide
# genuine staleness.
return current > self._boot_repo_mtime + 2.0
return current != self._boot_git_sha
def _trigger_stale_code_restart(self) -> None:
"""Idempotently kick off a graceful restart after stale-code detection.
@ -2782,12 +2931,17 @@ class GatewayRunner:
if self._stale_code_restart_triggered:
return
self._stale_code_restart_triggered = True
current_sha = None
try:
current_sha = self._current_git_sha_cached()
except Exception:
pass
logger.warning(
"Stale-code self-check: source files newer than gateway boot "
"time (boot=%.0f, newest=%.0f) — requesting graceful restart. "
"Stale-code self-check: git HEAD moved since gateway boot "
"(boot=%s, current=%s) — requesting graceful restart. "
"See Issue #17648.",
self._boot_repo_mtime,
_compute_repo_mtime(self._repo_root_for_staleness),
(self._boot_git_sha or "?")[:12],
(current_sha or "?")[:12],
)
try:
self.request_restart(detached=False, via_service=True)