Consume Finish Today (Wrap-up Guidance) V1 in headsdown-pi

[jsmestad]

What

Implement Finish Today (Wrap-up Guidance) V1 consumption in headsdown-pi so Pi can automatically steer toward the smallest safe shippable outcome when wrap-up is active, while preserving an explicit per-task full-depth override.

Why

headsdown-pi is a primary behavior surface for HeadsDown-guided agent execution. Once the shared API/SDK contract lands, Pi should consume the same structured guidance so behavior is consistent with VS Code and Claude surfaces.

Acceptance Criteria

1. headsdown_status output includes wrapUpGuidance when present, and keeps current output shape backward compatible.
2. before_agent_start context injection includes a concise, explicit Finish Today summary when active (state, remaining time/deadline, and intent).
3. headsdown_propose supports a per-task delivery override (auto, wrap_up, full_depth) and passes it through to SDK proposal input when provided.
4. HeadsDown skill guidance is updated so Pi behavior changes when wrap-up is active: completion-first execution, defer non-critical decisions, concise handoff.
5. Opt-out behavior is explicit and local to the task/session by default (no silent global disable).
6. Tests cover active/inactive guidance parsing, context formatting, and override pass-through behavior.
7. Existing non-wrap-up behavior remains unchanged for users on older APIs or with inactive guidance.

Developer Notes

Dependency: https://github.com/headsdownapp/heads_down/issues/812

Approach: Keep server guidance semantic and client behavior deterministic. Do not implement provider-specific model switching in this ticket.

Likely files:

• extensions/headsdown/index.ts
• extensions/headsdown/policy.ts (formatting only if needed)
• skills/headsdown/SKILL.md
• test/extension.test.ts
• test/availability-compat.test.ts

Testing:

• Unit tests for wrap-up fields in status/context payloads.
• Unit tests for deliveryMode (or equivalent) proposal input wiring.
• Compatibility tests for missing guidance fields.