fix(sessions): updateLastRoute must not bump updatedAt (#49515) (#49588) updateLastRoute() used mergeSessionEntry which bumps updatedAt to Date.now() on every inbound message. This prevented session idle and daily reset from ever firing, since evaluateSessionFreshness() always saw a fresh updatedAt. The fix from #32379 patched recordSessionMetaFromInbound to use mergeSessionEntryPreserveActivity, but missed updateLastRoute() in the same inbound pipeline. Changes: - Remove explicit updatedAt from updateLastRoute basePatch - Switch from mergeSessionEntry to mergeSessionEntryPreserveActivity - Add regression test verifying updatedAt is preserved - Update existing test assertion to match corrected behavior Fixes #49515