Five review findings folded:
- schema cache writes via utils.atomic_json_write (fsync; was bare
tmp+replace), file moved to cache/mcp_schema_cache.json with 0o600
(sibling precedent: registry discovery cache)
- phantom-tool reconciliation: after a lazy server's first-use connect,
cached tools the live server no longer offers are deregistered (were
permanent registry ghosts burning circuit-breaker strikes on every
'Unknown tool' round-trip); stale fingerprint logged
- cache-load path now runs _scan_mcp_description like the eager path
(cache file is user-writable JSON; defense-in-depth)
- write-through skips the disk rewrite when the entry is unchanged
(a flapping stdio server was rewriting byte-identical JSON per
revival)
- _lazy_server_fingerprints no longer write-only dead state (consumed
by the reconciliation logging)
444 mcp tests green (440 pre-fold + 4 new guards); phantom-dereg and
write-skip mutation-checked.
Stores per-server tool manifests in ~/.hermes/mcp_schema_cache.json so
tools can be registered into the agent snapshot without spawning the
stdio child at startup. Entries are keyed by server name plus a
fingerprint of the connection-defining config (command/args/url/
transport/tool filters), so any config change invalidates the entry.
Extracted from #56832.
kshitij
Vansh Gilhotra