fix(memory): add session-refresh guard to maybe_consolidate_by_tokens

When background consolidation runs with a stale session reference (captured
before AutoCompact replaced the session via compact_idle_session), it could
operate on outdated data. Now, after acquiring the per-session lock, the
method refreshes its session reference from SessionManager.get_or_create().
If the session was replaced, it swaps in the fresh reference before doing
any consolidation work.

This prevents a race where AutoCompact truncates an idle session while a
background maybe_consolidate_by_tokens call is in flight with the old
session object.

nanobot/agent/memory.py

@@ -683,6 +683,11 @@ class Consolidator:
 
         lock = self.get_lock(session.key)
         async with lock:
+            # Refresh session reference: AutoCompact may have replaced it.
+            fresh = self.sessions.get_or_create(session.key)
+            if fresh is not session:
+                session = fresh
+
             budget = self._input_token_budget
             target = int(budget * self.consolidation_ratio)
             last_summary = await self._consolidate_replay_overflow(