Wires the host's mirror hook end-to-end: FindGeminiSessionFile resolves
~/.gemini/tmp/<workspace>/chats/session-<ISO>-<sid_prefix>.jsonl from
the session id captured into .plexum-gemini-session, picking the
most-recent match by mtime. Logs the no-op for telemetry.
Real rewrite is deferred to v2: gemini-cli's tool-call id namespace
doesn't match Plexum's canonical block format (and its on-disk shape
is `$set`-style mutation log rather than flat append-only). When
tool-call round-trip through gemini's native surface lands, the
rewriter plugs into this file's path resolver.
hzhang
dbe68a889c