Retry is node-self only.
Retry keeps the same assignment.
Retry creates a new attempt.
Retry always uses `full_prompt`.
Retry durable handover comes from:
- the same assignment
- the prior terminal checkpoint written through `record_checkpoint`
- current surfaced `consumed_durable_refs`
- any optional `transient_refs`
- any relevant `task_memory_search_hints`
Do not treat same-session continuation as retry.
Do not depend on prior live session memory for retry.
