fix(session): opt the background-review fork out of session finalization

The background-review fork (fires ~every 10 turns) pins
review_agent.session_id = agent.session_id — the parent's LIVE id — for
prefix-cache parity, then calls close(). With session finalization now in
close(), that would end the still-active parent session mid-conversation.
Set _end_session_on_close = False on the fork so the real owner (CLI close /
gateway reset / cron) finalizes the session instead.

Follow-up to the #12029 fix.

agent/background_review.py

@@ -575,6 +575,13 @@ def _run_review_in_thread(
             # if a future code path bypasses the cache.
             review_agent.session_start = agent.session_start
             review_agent.session_id = agent.session_id
+            # The fork shares the parent's live session_id (pinned above for
+            # prefix-cache parity). It is single-lifecycle and calls close()
+            # right after this run_conversation(); without opting out, close()
+            # would finalize the parent's still-active session row mid
+            # conversation (the review fires every ~10 turns). Leave session
+            # finalization to the real owner (CLI close / gateway reset / cron).
+            review_agent._end_session_on_close = False
             # Never let the review fork compress. It shares the parent's
             # session_id, so if it won a compression race it would rotate the
             # parent into a NEW child that the gateway never adopts (the fork

tests/run_agent/test_background_review.py

@@ -76,6 +76,50 @@ def test_background_review_shuts_down_memory_provider_before_close(monkeypatch):
     ]
 
 
+def test_background_review_fork_opts_out_of_session_finalization(monkeypatch):
+    """The review fork shares the parent's live session_id, so it must set
+    ``_end_session_on_close = False``. Otherwise close() (now finalizing owned
+    session rows) would end the still-active parent session mid-conversation
+    every time the review fires (~every 10 turns). Regression for #12029.
+    """
+    seen = {}
+
+    class FakeReviewAgent:
+        def __init__(self, **kwargs):
+            self._session_messages = []
+            # Default matches AIAgent.__init__ (agent_init.py): owns its row.
+            self._end_session_on_close = True
+
+        def __setattr__(self, name, value):
+            object.__setattr__(self, name, value)
+            if name == "_end_session_on_close":
+                seen["end_session_on_close"] = value
+
+        def run_conversation(self, **kwargs):
+            # By the time the fork runs, the opt-out must already be applied.
+            seen["at_run_time"] = self._end_session_on_close
+
+        def shutdown_memory_provider(self):
+            pass
+
+        def close(self):
+            pass
+
+    monkeypatch.setattr(run_agent_module, "AIAgent", FakeReviewAgent)
+    monkeypatch.setattr(run_agent_module.threading, "Thread", ImmediateThread)
+
+    agent = _bare_agent()
+
+    AIAgent._spawn_background_review(
+        agent,
+        messages_snapshot=[{"role": "user", "content": "hello"}],
+        review_memory=True,
+    )
+
+    assert seen.get("end_session_on_close") is False
+    assert seen.get("at_run_time") is False
+
+
 def test_background_review_summarizer_receives_captured_messages_after_close(monkeypatch):
     """The action summarizer must see review messages even after close cleanup.