Identify a completed merged assistant handoff from the carrier's own stop state instead of an unrelated adjacent history row. Keep carriers with pending tool calls actionable so compaction cannot abort a live tool chain.
Treat a merged assistant-role summary carrier as the driving reference handoff when it immediately follows a completed assistant stop. Its preserved prose and stale tool_calls are assistant continuity, not a fresh live user request.
Keep legitimate in-flight behavior unchanged when there is no completed stop, a real user turn follows, or a distinct later assistant tool-call row continues the loop.
Extends the #80622 active-turn guard for the merged-carrier shape reported under #42768.
Pin #80622 invariants: handoff alone must not drive a model call after
stop, pending real users are restored, and synthetic compaction rows are
never treated as user-originated turns. Also give micro-compaction
enough passes to pay back the longer SUMMARY_PREFIX marker overhead.
poisdahl