plugins/context_engine.load_context_engine scanned only the bundled directory. An engine
dropped into $HERMES_HOME/plugins/<name> with `context.engine: <name>` was reachable only
through the general plugin system, which skips any user plugin not listed in
plugins.enabled — so every agent init logged "Context engine '<name>' not found — falling
back to built-in compressor" although the engine was installed and named in config.
Live probe on base (fake HOME, plugins/ctx_demo with register(ctx), context.engine:
ctx_demo): the warning fired on EVERY init, not only the first; adding the plugin to
plugins.enabled made it load through the general fallback. `context.engine` is the
activation signal (as memory.provider / cron.provider are for their kinds), so the engine
loader now resolves bundled then user dirs the way plugins/cron_providers does: same
`user_plugins_dir()` seam, cheap source heuristic (register_context_engine / ContextEngine),
user engines imported under a synthetic namespace, bundled wins on collision, and
discover_context_engines() lists them for `hermes plugins` / the dashboard.
Fixes#61839
credit: @giggling-ginger #61995
The Sep 2026 decomposition (PR #102117) makes internal import paths a non-API: names now live in
the focused modules that define them. This commit is the ONLY thing keeping the old paths alive,
so external plugins have time to update. It is deliberately a single, unsquashed commit:
git revert <this sha>
removes every shim, stub and manifest at once on the announced date. Nothing in-tree may depend on
these pointers: scripts/check_compat_pointers.py (wired into lint.yml) fails CI if it does.
What it adds (see COMPAT_MANIFEST.md, compat_manifest.json):
- 332 facade modules get one delimited `PLUGIN-COMPAT` block appended at the end of the file
- 1,172 moved names resolved lazily via a module `__getattr__` (PEP 562) — never a top-level import,
so no import cycles; facades that already had `__getattr__` get a chained one
- 592 third-party/stdlib names the old modules used to expose, with their original import statements
- 266 public definitions that had been deleted as unused, restored byte-for-byte from the pre-decomposition
tree (+40 private helpers and 16 imports pulled in only because a restored definition needs them)
- 3 deleted modules recreated as re-export stubs (gateway/startup_watchdog, hermes_cli/observability/
relay_runtime, tools/environments/modal_utils)
- private names (`_x`) get no pointer: they were never API (3,792 skipped)
Verified: all 335 touched modules import under a fresh HERMES_HOME and every manifest name resolves;
the lint reports zero in-tree uses; ruff clean; targeted suites unchanged.
Condenses the substance of PRs #16453, #17453, #16451, #17600, and #13373
into a minimal generic host contract that external context engine plugins
(e.g. hermes-lcm) need to integrate cleanly. Drops scaffolding that
duplicated existing infrastructure or had marginal value.
Five concrete changes:
1. `_transition_context_engine_session()` on AIAgent — generic lifecycle
helper that fires on_session_end → on_session_reset → on_session_start
→ optional carry_over_new_session_context. Engines implement only the
hooks they need; missing hooks are skipped. Built-in compressor keeps
its existing reset-only behavior because callers default to no
metadata. `reset_session_state()` now optionally accepts
previous_messages / old_session_id / carry_over_context and delegates
to the transition helper when provided. (#16453)
2. `conversation_id` passed to `on_session_start()` — both the
agent-init call site and the compression-boundary call site now
forward `self._gateway_session_key` so plugin engines have a stable
conversation identity that survives session_id rotation (compression
splits, /new, resume). The key already existed on AIAgent; it just
wasn't reaching engines. (#16453)
3. Canonical cache buckets forwarded to engines — the usage dict passed
to `update_from_response()` now includes input_tokens, output_tokens,
cache_read_tokens, cache_write_tokens, and reasoning_tokens on top of
the legacy prompt/completion/total keys. Engines can make decisions on
cache-hit ratios and reasoning costs instead of only aggregates. ABC
docstring updated. (#17453)
4. Plugin-registered context engines visible in the picker —
`_discover_context_engines()` in plugins_cmd.py now also includes
engines registered via `ctx.register_context_engine()` from plugin
manifests, deduplicating by name so repo-shipped descriptions win on
collision. (#16451)
5. `_EngineCollector.register_command()` — context engines using the
standard `register(ctx)` pattern can now expose slash commands (e.g.
`/lcm`). Routes to the global plugin command registry with the same
conflict-rejection policy regular plugins use (no shadowing built-ins,
no clobbering other plugins). Previously these calls hit a no-op and
the slash commands silently never appeared. (#17600)
Dropped from the original 5 PRs:
- Compression boundary signal (`boundary_reason="compression"`) from
#16453 — already on main at `agent/conversation_compression.py:412-424`,
landed via the bg-review extraction.
- `discover_plugins()` before fallback in run_agent.py from #16451 —
redundant: `get_plugin_context_engine()` already routes through
`_ensure_plugins_discovered()` which is idempotent.
- Runtime identity diagnostics method + helpers from #13373 (+251 LOC) —
operators can already read engine state via `engine.get_status()`;
the diagnostics view added marginal value relative to its surface area.
- The 553-LOC slash-command machinery from #17600 — replaced with a
20-LOC `register_command` method on the collector that reuses the
existing plugin command registry instead of building a parallel one.
Net: ~215 LOC of host-contract changes + 282 LOC of focused tests, vs
~1,176 LOC across the original 5 PRs.
Co-authored-by: Tosko4 <1294707+Tosko4@users.noreply.github.com>
Closes#16453.
Closes#17453.
Closes#16451.
Closes#17600.
Closes#13373.
Related: stephenschoettler/hermes-lcm#68.
## Why
Hermes supports Linux, macOS, and native Windows, but the codebase grew up
POSIX-first and has accumulated patterns that silently break (or worse,
silently kill!) on Windows:
- `os.kill(pid, 0)` as a liveness probe — on Windows this maps to
CTRL_C_EVENT and broadcasts Ctrl+C to the target's entire console
process group (bpo-14484, open since 2012).
- `os.killpg` — doesn't exist on Windows at all (AttributeError).
- `os.setsid` / `os.getuid` / `os.geteuid` — same.
- `signal.SIGKILL` / `signal.SIGHUP` / `signal.SIGUSR1` — module-attr
errors at runtime on Windows.
- `open(path)` / `open(path, "r")` without explicit encoding= — inherits
the platform default, which is cp1252/mbcs on Windows (UTF-8 on POSIX),
causing mojibake round-tripping between hosts.
- `wmic` — removed from Windows 10 21H1+.
This commit does three things:
1. Makes `psutil` a core dependency and migrates critical callsites to it.
2. Adds a grep-based CI gate (`scripts/check-windows-footguns.py`) that
blocks new instances of any of the above patterns.
3. Fixes every existing instance in the codebase so the baseline is clean.
## What changed
### 1. psutil as a core dependency (pyproject.toml)
Added `psutil>=5.9.0,<8` to core deps. psutil is the canonical
cross-platform answer for "is this PID alive" and "kill this process
tree" — its `pid_exists()` uses `OpenProcess + GetExitCodeProcess` on
Windows (NOT a signal call), and its `Process.children(recursive=True)`
+ `.kill()` combo replaces `os.killpg()` portably.
### 2. `gateway/status.py::_pid_exists`
Rewrote to call `psutil.pid_exists()` first, falling back to the
hand-rolled ctypes `OpenProcess + WaitForSingleObject` dance on Windows
(and `os.kill(pid, 0)` on POSIX) only if psutil is somehow missing —
e.g. during the scaffold phase of a fresh install before pip finishes.
### 3. `os.killpg` migration to psutil (7 callsites, 5 files)
- `tools/code_execution_tool.py`
- `tools/process_registry.py`
- `tools/tts_tool.py`
- `tools/environments/local.py` (3 sites kept as-is, suppressed with
`# windows-footgun: ok` — the pgid semantics psutil can't replicate,
and the calls are already Windows-guarded at the outer branch)
- `gateway/platforms/whatsapp.py`
### 4. `scripts/check-windows-footguns.py` (NEW, 500 lines)
Grep-based checker with 11 rules covering every Windows cross-platform
footgun we've hit so far:
1. `os.kill(pid, 0)` — the silent killer
2. `os.setsid` without guard
3. `os.killpg` (recommends psutil)
4. `os.getuid` / `os.geteuid` / `os.getgid`
5. `os.fork`
6. `signal.SIGKILL`
7. `signal.SIGHUP/SIGUSR1/SIGUSR2/SIGALRM/SIGCHLD/SIGPIPE/SIGQUIT`
8. `subprocess` shebang script invocation
9. `wmic` without `shutil.which` guard
10. Hardcoded `~/Desktop` (OneDrive trap)
11. `asyncio.add_signal_handler` without try/except
12. `open()` without `encoding=` on text mode
Features:
- Triple-quoted-docstring aware (won't flag prose inside docstrings)
- Trailing-comment aware (won't flag mentions in `# os.kill(pid, 0)` comments)
- Guard-hint aware (skips lines with `hasattr(os, ...)`,
`shutil.which(...)`, `if platform.system() != 'Windows'`, etc.)
- Inline suppression with `# windows-footgun: ok — <reason>`
- `--list` to print all rules with fixes
- `--all` / `--diff <ref>` / staged-files (default) modes
- Scans 380 files in under 2 seconds
### 5. CI integration
A GitHub Actions workflow that runs the checker on every PR and push is
staged at `/tmp/hermes-stash/windows-footguns.yml` — not included in this
commit because the GH token on the push machine lacks `workflow` scope.
A maintainer with `workflow` permissions should add it as
`.github/workflows/windows-footguns.yml` in a follow-up. Content:
```yaml
name: Windows footgun check
on:
push:
branches: [main]
pull_request:
branches: [main]
jobs:
check:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- uses: actions/setup-python@v5
with: {python-version: "3.11"}
- run: python scripts/check-windows-footguns.py --all
```
### 6. CONTRIBUTING.md — "Cross-Platform Compatibility" expansion
Expanded from 5 to 16 rules, each with message, example, and fix.
Recommends psutil as the preferred API for PID / process-tree operations.
### 7. Baseline cleanup (91 → 0 findings)
- 14 `open()` sites → added `encoding='utf-8'` (internal logs/caches) or
`encoding='utf-8-sig'` (user-editable files that Notepad may BOM)
- 23 POSIX-only callsites in systemd helpers, pty_bridge, and plugin
tool subprocess management → annotated with
`# windows-footgun: ok — <reason>`
- 7 `os.killpg` sites → migrated to psutil (see §3 above)
## Verification
```
$ python scripts/check-windows-footguns.py --all
✓ No Windows footguns found (380 file(s) scanned).
$ python -c "from gateway.status import _pid_exists; import os
> print('self:', _pid_exists(os.getpid())); print('bogus:', _pid_exists(999999))"
self: True
bogus: False
```
Proof-of-repro that `os.kill(pid, 0)` was actually killing processes
before this fix — see commit `1cbe39914` and bpo-14484. This commit
removes the last hand-rolled ctypes path from the hot liveness-check
path and defers to the best-maintained cross-platform answer.
Follow-up fixes for the context engine plugin slot (PR #5700):
- Enhance ContextEngine ABC: add threshold_percent, protect_first_n,
protect_last_n as class attributes; complete update_model() default
with threshold recalculation; clarify on_session_end() lifecycle docs
- Add ContextCompressor.update_model() override for model/provider/
base_url/api_key updates
- Replace all direct compressor internal access in run_agent.py with
ABC interface: switch_model(), fallback restore, context probing
all use update_model() now; _context_probed guarded with getattr/
hasattr for plugin engine compatibility
- Create plugins/context_engine/ directory with discovery module
(mirrors plugins/memory/ pattern) — discover_context_engines(),
load_context_engine()
- Add context.engine config key to DEFAULT_CONFIG (default: compressor)
- Config-driven engine selection in run_agent.__init__: checks config,
then plugins/context_engine/<name>/, then general plugin system,
falls back to built-in ContextCompressor
- Wire on_session_end() in shutdown_memory_provider() at real session
boundaries (CLI exit, /reset, gateway expiry)
