test: add prefetch_context observer-resolution test for ai_observe_others

Verify that get_prefetch_context queries user context through the
assistant observer when _ai_observe_others is enabled, matching
the fix that routes _fetch_session_context through
_resolve_observer_target.

tests/honcho_plugin/test_session.py

@@ -361,6 +361,46 @@ class TestPeerLookupHelpers:
         user_peer.context.assert_called_once_with(target=session.user_peer_id)
         ai_peer.context.assert_called_once_with(target=session.assistant_peer_id)
 
+    def test_get_prefetch_context_uses_assistant_observer_for_user_when_ai_observe_others(self):
+        """With ai_observe_others enabled, get_prefetch_context must query
+        the user context through the assistant observer, not the user peer."""
+        mgr, session = self._make_cached_manager()
+        mgr._ai_observe_others = True
+
+        assistant_peer = MagicMock()
+
+        def _assistant_context(**kwargs):
+            if kwargs.get("target") == session.user_peer_id:
+                return SimpleNamespace(
+                    representation="User via assistant",
+                    peer_card=["Name: Robert"],
+                )
+            if kwargs.get("target") == session.assistant_peer_id:
+                return SimpleNamespace(
+                    representation="AI self",
+                    peer_card=["Role: Assistant"],
+                )
+            return SimpleNamespace(representation="Unknown", peer_card=[])
+
+        assistant_peer.context.side_effect = _assistant_context
+        mgr._get_or_create_peer = MagicMock(
+            side_effect=[assistant_peer, assistant_peer],
+        )
+
+        result = mgr.get_prefetch_context(session.key)
+
+        assert result == {
+            "representation": "User via assistant",
+            "card": "Name: Robert",
+            "ai_representation": "AI self",
+            "ai_card": "Role: Assistant",
+        }
+        assert assistant_peer.context.call_count == 2
+        assistant_peer.context.assert_any_call(
+            target=session.user_peer_id, search_query=None,
+        )
+        assistant_peer.context.assert_any_call(target=session.assistant_peer_id)
+
     def test_get_ai_representation_uses_peer_api(self):
         mgr, session = self._make_cached_manager()
         ai_peer = MagicMock()