* fix(agent): search all agent stores when resolving --session-id
When `--session-id` was provided without `--to` or `--agent`, the reverse
lookup only searched the default agent's session store. Sessions created
under a specific agent (e.g. `--agent mybot`) live in that agent's store
file, so the lookup silently failed and the session was not reused.
Now `resolveSessionKeyForRequest` iterates all configured agent stores
when the primary store doesn't contain the requested sessionId.
Fixes#12881
* fix: search other agent stores when --to key does not match --session-id
When --to derives a session key whose stored sessionId doesn't match the
requested --session-id, the cross-store search now also runs. This handles
the case where a user provides both --to and --session-id targeting a
session in a different agent's store.
