implement

implement

Use this skill to implement an approved PRD or a clearly scoped task end to end.

This is the execution counterpart to prd.

implement owns the loop that drives a task to done, including fixing. It does not reimplement verification: it delegates judgment to verify as the gate of its loop (see Final Verification). verify stays the single source of truth for how to judge done, and can still be run standalone for an independent audit on any diff.

Inputs

When the task came from prd, read the artifacts under .dev/<topic-slug>/:

• prd.md - the contract: scope, non-goals, requirements, acceptance criteria, tasks, and the verification plan. The acceptance criteria are the rubric the verifier checks against.
• checklist.md - the task checklist. Adopt it as the live checklist instead of regenerating one.
• context-notes.md - project grounding. Read it to avoid re-exploring what prd already established.

If those artifacts do not exist (the user handed a scoped task, linked spec, or request directly), fall back to that single source document and build the checklist from it.

Readiness Check

Before editing code:

1. Read the inputs above (the .dev/<slug>/ artifacts, or the single source document on the fallback path).
2. Identify scope, non-goals, requirements, acceptance criteria, and verification.
3. Check git status --short.
4. Read the actual files likely to be touched.
5. Stop and ask if required pre-work, credentials, product decisions, destructive data changes, or structural approval are missing.

Live Checklist

Adopt checklist.md as the working checklist when it exists. Otherwise create one from the source document.

Track:

• requirements
• acceptance criteria
• implementation tasks
• verification commands
• browser or runtime QA scenarios
• human checks

Do not mark a task complete until its acceptance criteria have evidence or a concrete blocker.

Seed A Structured Task List

When checklist.md exists and has 3 or more tasks, seed a structured task list from it with TaskCreate instead of a flat TodoWrite. This keeps requirement traceability, ordering, and evidence attached to each task through the loop.

For each T<n> task in checklist.md:

1. TaskCreate one task. Carry the checklist tags into metadata:
   • metadata.req - the (req: ...) ids.
   • metadata.ac - the (ac: ...) ids it is responsible for.
   • metadata.checklistId - the T<n> id, so after: can be resolved.
2. After all tasks exist, wire ordering: for each (after: T1) tag, set addBlockedBy on the dependent task pointing at the prerequisite's task id.
3. Leave acceptance criteria and human checks in the markdown checklist; the task list tracks the buildable work, the verifier judges the criteria.

Fall back to TodoWrite when there is no checklist.md, the task count is small, or the work is a single straightforward change. Do not seed a structured task list for trivial tasks - the ceremony is not worth it.

Implementation Loop

Work tasks in dependency order. When using the structured task list, pick the next task whose blockedBy is empty (lowest checklistId first); never start a task that is still blocked.

For each task:

1. Mark it in_progress (TaskUpdate) before editing, so progress is visible.
2. Re-read the relevant files.
3. Make the smallest change that satisfies the mapped requirement (metadata.req).
4. Avoid unrelated refactors.
5. Preserve user-owned worktree changes.
6. Run the smallest useful check after meaningful edits.
7. Verify the mapped acceptance criteria (metadata.ac) inline, at the level the criterion actually needs - do not defer all verification to the final pass:
   • Machine-checkable criteria (SQL query, curl, build, unit test, generated output) -> run the check now and capture the real output.
   • Runtime/browser criteria -> exercise the flow now if you can (the same playwright-cli the verifier would use); if a real prerequisite blocks it (e.g. an OAuth login you cannot automate), record it as a concrete blocker rather than assuming it passes.
8. Record evidence as you go - store it on the task (metadata.evidence: command run, file:line, observed result) so the final verifier can build on it instead of starting from zero.
9. Mark completed only when the mapped acceptance criteria (metadata.ac) have real evidence or a concrete blocker. Reading the code and assuming it works is not evidence. A partial or unproven change keeps the task in_progress.

If a new task is needed, add it (TaskCreate) only when it maps to an approved requirement or is pure verification/release hygiene; tag its metadata.req. Ask before adding new product scope or materially changing the approved structure.

Final Verification

Finish the implementation first. Then, once, delegate the completion verdict to an independent verifier instead of judging it yourself.

The same context that wrote the change is the worst judge of it. So when the build is done, spawn a fresh verifier that did not write the code and let it judge against the acceptance criteria.

1. Spawn one independent verifier subagent with the Task tool. Give it:
   • the acceptance criteria from prd.md (or the task) as the rubric - every criterion, not a subset,
   • both the PRD's Verification - Agent and Verification - Human sections as the available methods. The verifier has the same tooling you do, including playwright-cli, so a criterion filed under Verification - Human is not automatically out of scope: if a browser/API/DB step can be driven without a human, the verifier runs it.
   • the changed scope (git status --short / the diff) and relevant files,
   • the evidence you collected while building. Instruct it to follow the verify skill: judge each acceptance criterion with the right verification level and report in the verify output format - an overall verdict plus a per-criterion result (checked / failed / not checked) with evidence. A criterion it can only confirm by reading code - never by running it - must be reported as Blocked (names the missing prerequisite, e.g. "needs an authenticated session"), not silently passed. The verifier is report-only - it does not modify code.
2. Read the verdict. verify returns Pass | Partial | Fail | Blocked plus the per-criterion detail. A Pass is only valid if every criterion has real evidence; treat a Pass that leaves runtime/browser criteria unchecked as Partial and push the verifier to actually run them.
   • Pass (all criteria met with evidence) -> done.
   • Partial or Fail -> fix the concrete gap (file, line, failing case) the verifier named, then run the verifier once more to confirm. Stop after that second pass; if it still fails, report the remaining gap rather than looping.
   • Blocked -> stop and report the blocker that needs a human or a decision. Surface it as a remaining item; do not bury it under a Pass.

Do not claim completion on a verdict you produced yourself, on skipped verification, or on a weaker target than the criteria asked for. Report the concrete gap.

Final Report

## Status

Done | Partially Done | Blocked

## Changed

- ...

## Acceptance Criteria

- AC1: Met | Not Met | Blocked - evidence

## Verification

- Command or scenario:
- Result:

## Human Check

- ...

## Risks

- ...