Record the `todo-plan` snapshot scenario: a real prompt drives the model to call
todo_write, and the golden captures the resulting `plan` sessionUpdate (three
entries, priority synthesized as medium, status 1:1) plus the persisted
todo/write event. Registered in SCENARIOS; replays deterministically keyless.
Add a with-key coding-agent e2e that verifies the WORLD — a real model call to
todo_write lands a todo/write event whose snapshot is a valid, one-in-progress
list — not the agent's self-report. Wire tool-todo into the e2e harness.