Daoyuan Li
cdefd4a8aa
fix(mcp): invalidate tools cache on config content + path, not just newer mtime ( #4124 ) ...
* fix(mcp): invalidate tools cache on config content + path, not just newer mtime
The MCP tools cache invalidated only on a strict extensions-config mtime `>`
comparison and tracked no resolved config path, so `_is_cache_stale()` missed:
- content changes with an unchanged mtime (same-second edits; object-store /
network mounts that do not bump mtime);
- content changes with a backward mtime (git checkout, cp -p / backup restore,
tar / rsync preserving timestamps);
- a resolved-path switch to a different config file with mtime <= the recorded
value (structurally invisible — no path was tracked at all).
On multi-worker (uvicorn/gunicorn) or stale-mtime deployments this leaves the
LangGraph-embedded runtime and every non-writer worker serving stale MCP tools
after `PUT /api/mcp/config`, breaking the module's documented promise that
changes made through the Gateway API are reflected in the embedded runtime.
Record the resolved config path and a `(mtime, size, sha256)` content signature
at initialization and invalidate when the path OR the signature differs (`!=`),
mirroring `config/app_config.py::get_app_config()` so the two runtime-editable
config files share one content-based staleness signal. The per-call stat was
already paid, and the small-file sha256 matches the cost app_config pays per
request. The "config missing / not yet initialized" no-op behavior and the
cache reset endpoint are preserved.
Adds backend/tests/test_mcp_cache.py covering all three failure modes plus
unchanged-file and forward-edit sanity cases. Also folds in an incidental
backend/AGENTS.md doc-sync: the restart-required field list was missing
`scheduler` and `run_ownership`, both present in
reload_boundary.py::STARTUP_ONLY_FIELDS.
* test(mcp): pin cache staleness contracts raised in review
Two review observations on the content-signature cache fix, both raised as
non-blocking design questions rather than bugs:
- Whether relying on mtime+size alone (skipping the sha256) could ever be
"optimized" back in, reopening the narrow same-second / identical-length
swap gap the signature was built to close.
- Whether the extensions config being deleted entirely after a successful
init leaves the cache in a defined state, since current_signature flips
to None and _is_cache_stale() returns False.
Neither is a behavior change: both were already the intended contract,
preserved verbatim from the pre-fix mtime-only code (which also returned
False once the file could no longer be stat-ed). Record the reasoning
inline and add regression tests that pin each contract so a future change
cannot alter either silently:
- test_same_mtime_same_size_swap_is_stale: a same-length server-name swap
that leaves mtime AND size unchanged (the precise scenario from review,
sharper than the existing same-mtime test, which also changes size) is
still caught only because the sha256 is computed unconditionally.
- test_config_deleted_after_init_is_not_stale: deleting the config file
after init keeps the cache serving its last-known-good MCP tools instead
of invalidating into an unconfigured state.
Both new tests were confirmed to fail against a deliberately reintroduced
version of the regression they guard (hash short-circuit / removed
None-guard), then confirmed to pass against the real code.
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