Save or resume a small delegated-task handoff in the existing plan

For a task that spans sessions, use the existing .pi/PLAN.md; do not introduce a second task database. Read it before changing anything. Preserve the user's plan and all content outside the bounded section below. If the marker already exists more than once, or its closing marker is missing, report the ambiguity rather than rewriting the file. Create the file only when it does not exist.

On save (the default), update only one section between these exact markers:

<!-- delegated-task:start -->
## Delegated task handoff
- Objective:
- Authorized scope and explicit approval boundaries:
- Target: repository, base/head, dirty-state fingerprint when available:
- Completed acceptance evidence: criterion, command/result, source transcript:
- Remaining work and unexercised criteria:
- Blocker or required decision:
- Next action:
<!-- delegated-task:end -->

Keep it short: source pointers rather than pasted logs; distinguish execution completion from verified acceptance. Preserve existing evidence with its original revision instead of silently relabeling it current. Do not copy credentials.

On resume, read the section and relevant evidence, then compare its revision and scope with current Git state and the user's latest request. Stale evidence must be rerun when needed; missing fingerprints mean identity is unverified. Report the next concrete action and unresolved decision. Reading the record does not authorize new work, enable subagents, launch children or resume them. Continue only work already authorized in the current conversation.