Execute Plan Phase

Work on one phase of an existing plan, then close the loop by updating the plan and PRD to reflect reality.

Quick start

User: "Work on phase 2 of docs/plans/feature-x.md"

1. Read the plan file and the linked PRD
2. Implement
3. Update plan + PRD

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Workflow

1. Load context

• Read the plan file (e.g. docs/plans/feature-x.md)
• Find the linked PRD (Source PRD: header) and read it too
• Identify which phase to work on — if the user didn't specify, pick the first phase whose acceptance criteria are not all checked

2. Implement

Work through the phase. Use manage_todo_list to track sub-tasks within the phase.

While implementing, note:

• Deviations: implementation details that differ from the plan description
• Discoveries: new constraints or integration details surfaced during work
• Scope changes: acceptance criteria that proved unnecessary, impossible, or need splitting

3. Update the plan file

After completing the phase (or reaching a stopping point), edit the plan file:

Always do:

• Check off completed acceptance criteria: - [ ] → - [x]
• Add a ### Notes section under the phase with implementation deviations and discoveries

If scope changed:

• Rewrite the ### What to build or acceptance criteria of future phases affected by what you learned
• Add or remove phases if the work revealed the breakdown was wrong
• Mark skipped criteria with ~~strikethrough~~ and a note explaining why

Phase completion marker — append at the top of the phase block when all criteria are met:

> ✅ Completed — <brief summary of what was built>

4. Update the PRD (only if needed)

Update the source PRD only when the implementation revealed that a PRD requirement was wrong, impossible, or needs re-scoping. Do not update the PRD for normal implementation detail choices.

Triggers that warrant a PRD update:

• A user story turned out to be technically infeasible as written
• A new integration constraint changes the expected UX or data model
• Scope was explicitly approved-down by the user during this session

When updating, add an ## Amendment section at the bottom of the PRD:

## Amendment — Phase N execution (<date>)

**Changed**: <what changed and why>
**Original text**: <quote the original>
**New text**: <the replacement>

Never silently rewrite PRD body text — only append amendments.

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Rules

• Work on one phase at a time — do not bleed into the next phase
• If you hit a blocker that requires solving something from a future phase, flag it and ask the user whether to proceed or re-sequence
• Keep plan updates surgical — only change what changed; preserve untouched phases exactly
• Do not rewrite acceptance criteria that are already checked off