fix(cli): pass session messages to shutdown_memory_provider (#15165 sibling)

The gateway fix in the previous commit forwards _session_messages on
gateway session teardown.  The CLI exit cleanup path had the same bug:
it read getattr(agent, 'conversation_history', None) or [] — but AIAgent
has no conversation_history attribute, so providers always received [].

Switch to _session_messages (same attribute the gateway now uses),
guarded by isinstance(..., list) to preserve the no-arg fallback for
MagicMock-based CLI test stubs.

Adds tests/cli/test_cli_shutdown_memory_messages.py (4 cases mirroring
the gateway suite).

cli.py

@@ -759,9 +759,17 @@ def _run_cleanup():
         pass
     try:
         if _active_agent_ref and hasattr(_active_agent_ref, 'shutdown_memory_provider'):
-            _active_agent_ref.shutdown_memory_provider(
-                getattr(_active_agent_ref, 'conversation_history', None) or []
-            )
+            # Forward the agent's own transcript so memory providers'
+            # ``on_session_end`` hooks see the real conversation instead of
+            # an empty list (#15165). ``_session_messages`` is set on
+            # ``AIAgent.__init__`` and refreshed every turn via
+            # ``_persist_session``. Fall back to no-arg on test stubs /
+            # partially-initialised agents where the attribute is missing.
+            _session_msgs = getattr(_active_agent_ref, '_session_messages', None)
+            if isinstance(_session_msgs, list):
+                _active_agent_ref.shutdown_memory_provider(_session_msgs)
+            else:
+                _active_agent_ref.shutdown_memory_provider()
     except Exception:
         pass