fix(agent): eliminate race condition in auto compact summary retrieval

Make Consolidator.archive() return the summary string directly instead
of writing to history.jsonl then reading back via get_last_history_entry().
This eliminates a race condition where concurrent _archive calls for
different sessions could read each other's summaries from the shared
history file (cross-user context leak in multi-user deployments).

Also removes Consolidator.get_last_history_entry() — no longer needed.

nanobot/agent/auto_compact.py

@@ -53,9 +53,7 @@ class AutoCompact:
                 return
             n = len(msgs)
             last_active = session.updated_at
-            await self.consolidator.archive(msgs)
+            summary = await self.consolidator.archive(msgs) or ""
-            entry = self.consolidator.get_last_history_entry()
-            summary = (entry or {}).get("content", "")
             if summary and summary != "(nothing)":
                 self._summaries[key] = (summary, last_active)
                 session.metadata["_last_summary"] = {"text": summary, "last_active": last_active.isoformat()}
@@ -71,6 +69,8 @@ class AutoCompact:
         if key in self._archiving or self._is_expired(session.updated_at):
             logger.info("Auto-compact: reloading session {} (archiving={})", key, key in self._archiving)
             session = self.sessions.get_or_create(key)
+        # Hot path: summary from in-memory dict (process hasn't restarted).
+        # Also clean metadata copy so stale _last_summary never leaks to disk.
         entry = self._summaries.pop(key, None)
         if entry:
             session.metadata.pop("_last_summary", None)

nanobot/agent/memory.py

@@ -374,10 +374,6 @@ class Consolidator:
             weakref.WeakValueDictionary()
         )
 
-    def get_last_history_entry(self) -> dict[str, Any] | None:
-        """Return the most recent entry from history.jsonl."""
-        return self.store._read_last_entry()
-
     def get_lock(self, session_key: str) -> asyncio.Lock:
         """Return the shared consolidation lock for one session."""
         return self._locks.setdefault(session_key, asyncio.Lock())
@@ -437,13 +433,13 @@ class Consolidator:
             self._get_tool_definitions(),
         )
 
-    async def archive(self, messages: list[dict]) -> bool:
+    async def archive(self, messages: list[dict]) -> str | None:
         """Summarize messages via LLM and append to history.jsonl.
 
-        Returns True on success (or degraded success), False if nothing to do.
+        Returns the summary text on success, None if nothing to archive.
         """
         if not messages:
-            return False
+            return None
         try:
             formatted = MemoryStore._format_messages(messages)
             response = await self.provider.chat_with_retry(
@@ -463,11 +459,11 @@ class Consolidator:
             )
             summary = response.content or "[no summary]"
             self.store.append_history(summary)
-            return True
+            return summary
         except Exception:
             logger.warning("Consolidation LLM call failed, raw-dumping to history")
             self.store.raw_archive(messages)
-            return True
+            return None
 
     async def maybe_consolidate_by_tokens(self, session: Session) -> None:
         """Loop: archive old messages until prompt fits within safe budget.

tests/agent/test_auto_compact.py

@@ -101,7 +101,7 @@ class TestAutoCompact:
         loop.sessions.save(s2)
 
         async def _fake_archive(messages):
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
         loop.auto_compact.check_expired(loop._schedule_background)
@@ -126,7 +126,7 @@ class TestAutoCompact:
 
         async def _fake_archive(messages):
             archived_messages.extend(messages)
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
 
@@ -147,12 +147,9 @@ class TestAutoCompact:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "User said hello."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User said hello.",
-        }
 
         await loop.auto_compact._archive("cli:test")
 
@@ -174,7 +171,7 @@ class TestAutoCompact:
         async def _fake_archive(messages):
             nonlocal archive_called
             archive_called = True
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
 
@@ -201,7 +198,7 @@ class TestAutoCompact:
         async def _fake_archive(messages):
             nonlocal archived_count
             archived_count = len(messages)
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
 
@@ -243,12 +240,9 @@ class TestAutoCompactIdleDetection:
 
         async def _fake_archive(messages):
             archived_messages.extend(messages)
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         # Simulate proactive archive completing before message arrives
         await loop.auto_compact._archive("cli:test")
@@ -311,7 +305,7 @@ class TestAutoCompactIdleDetection:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
 
@@ -340,12 +334,9 @@ class TestAutoCompactSystemMessages:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         # Simulate proactive archive completing before system message arrives
         await loop.auto_compact._archive("cli:test")
@@ -428,12 +419,9 @@ class TestAutoCompactEdgeCases:
 
         async def _fake_archive(messages):
             archived_messages.extend(messages)
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         # Simulate proactive archive completing before message arrives
         await loop.auto_compact._archive("cli:test")
@@ -518,12 +506,9 @@ class TestAutoCompactIntegration:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         # Simulate proactive archive completing before message arrives
         await loop.auto_compact._archive("cli:test")
@@ -586,12 +571,9 @@ class TestProactiveAutoCompact:
 
         async def _fake_archive(messages):
             archived_messages.extend(messages)
-            return True
+            return "User chatted about old things."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User chatted about old things.",
-        }
 
         await self._run_check_expired(loop)
 
@@ -635,7 +617,7 @@ class TestProactiveAutoCompact:
             archive_count += 1
             started.set()
             await block_forever.wait()
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _slow_archive
 
@@ -688,7 +670,7 @@ class TestProactiveAutoCompact:
         async def _fake_archive(messages):
             nonlocal archive_called
             archive_called = True
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
 
@@ -712,12 +694,9 @@ class TestProactiveAutoCompact:
         async def _fake_archive(messages):
             nonlocal archive_count
             archive_count += 1
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         # First tick: archives the session
         await self._run_check_expired(loop)
@@ -741,7 +720,7 @@ class TestProactiveAutoCompact:
         async def _fake_archive(messages):
             nonlocal archive_count
             archive_count += 1
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
 
@@ -769,12 +748,9 @@ class TestProactiveAutoCompact:
         async def _fake_archive(messages):
             nonlocal archive_count
             archive_count += 1
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         # First compact cycle
         await loop.auto_compact._archive("cli:test")
@@ -810,12 +786,9 @@ class TestSummaryPersistence:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "User said hello."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User said hello.",
-        }
 
         await loop.auto_compact._archive("cli:test")
 
@@ -839,12 +812,9 @@ class TestSummaryPersistence:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "User said hello."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User said hello.",
-        }
 
         # Archive
         await loop.auto_compact._archive("cli:test")
@@ -874,12 +844,9 @@ class TestSummaryPersistence:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         await loop.auto_compact._archive("cli:test")
 
@@ -908,12 +875,9 @@ class TestSummaryPersistence:
         loop.sessions.save(session)
 
         async def _fake_archive(messages):
-            return True
+            return "Summary."
 
         loop.consolidator.archive = _fake_archive
-        loop.consolidator.get_last_history_entry = lambda: {
-            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
-        }
 
         await loop.auto_compact._archive("cli:test")
 

tests/agent/test_consolidator.py

@@ -46,7 +46,7 @@ class TestConsolidatorSummarize:
             {"role": "assistant", "content": "Done, fixed the race condition."},
         ]
         result = await consolidator.archive(messages)
-        assert result is True
+        assert result == "User fixed a bug in the auth module."
         entries = store.read_unprocessed_history(since_cursor=0)
         assert len(entries) == 1
 
@@ -55,14 +55,14 @@ class TestConsolidatorSummarize:
         mock_provider.chat_with_retry.side_effect = Exception("API error")
         messages = [{"role": "user", "content": "hello"}]
         result = await consolidator.archive(messages)
-        assert result is True  # always succeeds
+        assert result is None  # no summary on raw dump fallback
         entries = store.read_unprocessed_history(since_cursor=0)
         assert len(entries) == 1
         assert "[RAW]" in entries[0]["content"]
 
     async def test_summarize_skips_empty_messages(self, consolidator):
         result = await consolidator.archive([])
-        assert result is False
+        assert result is None
 
 
 class TestConsolidatorTokenBudget: