TodoList reminder misses turn-end reconciliation (unfinished todos after turn end)

Problem

The TodoListReminderInjector (packages/agent-core/src/agent/injection/todo-list.ts) only nudges after 10 assistant turns since the last TodoList write (and 10 since the last reminder).

This misses a common case: the agent finishes the actual work, ends the turn, but forgets to mark todos done. The turn is over in well under 10 turns, so no reminder ever fires — the todo list stays stale (pending/in_progress) with nothing to reconcile it.

Expected behavior

When a turn ends (the latest assistant step made no tool calls) with unfinished todos and no TodoList write on the way out, the next step should get a reminder right away instead of waiting out the full cadence:

• If the work is actually complete → mark items done / clear the stale list
• If items remain → continue with them

To keep it from nagging, the turn-end rule has its own spacing (3 assistant turns since the last reminder) and does not fire when every todo is done or when the final step was itself a TodoList write. The existing 10-turn cadence rule is unchanged.

Notes

• The change is confined to TodoListReminderInjector plus tests.
• Mid-turn detection uses the existing history shape: the latest assistant message having no tool calls means the turn completed.

I have a patch ready with tests (10 injector tests passing, typecheck/lint clean) and will open a PR referencing this issue.

Start with packages/agent-core/src/agent/injection/todo-list.ts and the existing injector tests. Check the history shape used to detect a completed turn and the current reminder cadence, then run the injector tests, typecheck, and lint. Done means unfinished todos trigger the turn-end reminder with the specified spacing while completed lists and final TodoList writes do not.