- Fire on_session_finalize and on_session_reset in gateway _handle_reset_command()
- Fire on_session_finalize during gateway stop() for each active agent
- Move CLI test from tests/ root to tests/cli/ (matches recent restructure)
- Add 5 gateway tests covering reset hooks, ordering, shutdown, and error handling
- Place on_session_reset after new session is guaranteed to exist (covers
the get_or_create_session fallback path)
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