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.
Wires the fingerprint-keyed schema cache (previous commit, @Vansh5632's
design from #56832) into the startup path, re-derived onto main's
current connect machinery:
- register_mcp_servers: servers with mcp_servers.<name>.lazy=true whose
config fingerprint matches a valid cache entry register tools from
cache WITHOUT spawning; miss/stale falls back to eager connect.
- First tool use routes through _ensure_lazy_server_connected, which
composes with the connect cooldown (#50394) and _server_connecting
dedup rather than duplicating the connect path.
- resource/prompt utility handlers (list_resources/get_prompt) also
connect-on-first-use — closes the gap flagged in the original
sweeper review.
- Write-through: a live connect refreshes the cache entry.
Config gate is per-server, default OFF, matching the
idle_timeout_seconds key pattern. 24 lazy/cache tests + 440 mcp-wide
green; mutation-checked (cache-read disabled -> registration test
fails; connect bypassed -> 3 first-use tests fail).
kshitij