Execute Phase

Step executor for units. The unit doc (created by unit-lane) owns Tasks P1…Pn, Evidence rows, and a Progress log — these replace PLAN.md, TASKS.md, progress.md, and ACCEPTANCE.md. Each step runs as an atomic gate/commit.

Argument resolution (first match):

• <NN-slug> P<k> — exactly the step named by the triage order (P1, P2, …)
• <NN-slug> (no step) — all remaining steps, one commit each
• P<k> alone — the step by position in the current unit (last-known NN-slug)

Never infer a step ID absent from the triage block in the unit doc.

Turn contract

Tick every box before ending the turn; an unchecked box means the turn is not done:

✓ Triage verified — unit doc Evidence section header matches
  `bun scripts/unit-route.mjs --triage <slug>` output block (PREFLIGHT.md)
✓ Unit doc read and step selected (explicit P<k> or first unfinished)
✓ Step executed and committed (one commit per step, conventional format)
✓ Evidence rows updated (command → exit/digest → output → verified-by)
✓ Progress log updated with a dated `YYYY-MM-DD HH:MM` entry (what, commit, next)
✓ Diff guard passed (on implement steps) — see `diff-guard` in PREFLIGHT.md
✓ → Next: block printed as the absolute last output

When to use

• A triaged unit from unit-lane: steps include implement/tests/evidence → invoke with <NN-slug> or <NN-slug> P<k>.
• Docs-only units (triage returns only [docs, evidence]) do not load this skill — they are executed in-place by the unit-lane conductor.
• To execute all remaining steps: <NN-slug> with no step argument.
• To repair a failed step: <NN-slug> P<k> (retry the same step).

Step 0 — Discover the project

Per the agent guide's Workflow conventions + documentation map, read the unit doc at docs/features/<NN-slug>/SPEC.md. Verify it carries ## Tasks (P1…Pn), ## Evidence, and ## Progress sections. If absent, the unit is not ready — stop and suggest unit-lane triage first.

Process

1. Verify triage currency

Run bun scripts/unit-route.mjs --triage <slug> and compare its block to the Evidence section header in the unit doc. Mismatch → STOP and re-triage first. This is the gate that ensures the executor and unit-lane agree on steps.

2. Select the step

If a step argument is given (e.g. P2), use that step. Otherwise, the first unfinished step — the first P in Tasks whose checkbox is unticked. Never execute a step the triage skipped.

3. Pre-step gates

Run gates in order; any fails → STOP (see PREFLIGHT.md):

1. Path-protection checkpoint — read the committed range against protected paths (e.g. tests/, fixtures/). Exit 1 → STOP with the gate rejection block. No --force bypass (no flag can override).
2. Phase-lint — run bun scripts/phase-lint.mjs <unit-doc> only when the step is implement and the unit has Tasks P1…Pn. Parse the Tasks section (not PLAN.md/TASKS.md). Exit 1 → STOP. If the script is absent, apply the eight phase-contract rules by hand, label weaker, and disclose.
3. Pre-write mapper — for implement steps, settle the pre-write mapper contract before branch creation, planning commit, or source/test edit: (implementation-discovery): it closes the seven evidence questions and routes READY | REPLAN | NEEDS-DESIGN | BLOCKED; only READY authorizes the first write.
4. Dependency/invariant checks — per unit-lane's triage catalog rules: ensure required dependencies are merged; architectural invariants preserved or backed by an explicit recorded decision (block violates/introduces/ changes before edits).

4. Execute the step

Follow the unit-lane reference for this step (references/STEPS.md catalog): one line — read the step's reference file, perform its checklist, commit the work. For implement steps: write tests-first where they pay (core/domain, orchestration — record the failing red run's command, exit, and failing test names before implementation), then green. UI/adapter glue may test after.

5. Post-step

1. Diff guard (implement steps only): run bun scripts/diff-guard.mjs --base <last-step-commit> --unit <unit> — paste the block verbatim. BREACH → STOP (re-triage or record exception). Anti-gaming: NEVER shrink a diff by deleting comments, blank lines, docs or tests.
2. Evidence rows: one row per AC satisfied — | AC | command | exit/digest | output (≤2 lines) | verified-by |. Append to the Evidence section.
3. Progress log: append a dated entry — YYYY-MM-DD HH:MM — <what was done> → <commit sha> — next: <what is next>.
4. Commit: git add <changed files> then git commit -m "<type>(<scope>): <step-summary>" — run it, paste the SHA.

6. Red gate (repair loop)

After each step: run the project's verification gate (type-check + tests + build).

• Gate green → proceed.

• Gate red → record exit code + failing test names in the Progress log, repair the same step, retry. Default --max-attempts 3 (user value overrides).

• Exhausted → STOP with:

  UNIT LOOP — <unit> BLOCKED at <P<k>>
  Reason: <NO-PROGRESS|ATTEMPT-BUDGET> · Attempts: <n>
  Last validator: <command> → <exit/status + compact failure>
  Preserved: no red commit; acceptance blob <sha> unchanged
  
  → Next: inspect the named blocker, then re-run /execute-phase <unit> <P<k>>
    · architecture/product decision required → resolve it before resuming
    · continue atomically → /execute-phase <unit> <P<k>>
  

7. Whole-unit mode

When invoked as <NN-slug> with no step: loop all remaining steps, one commit each. After each step: gates, execute, diff guard (if implement), evidence/ progress update, commit. Skip intermediate review checkpoints; the mandatory end review covers the full accumulated diff. On gate red at any step: repair that step (up to --max-attempts), then continue the loop. Terminal:

UNIT LOOP — <unit> COMPLETE
Steps: <n> · Commits: <sha list> · Gate: PASS
PR: <url>

→ Next: /review-change on the changed HEAD — the mandatory end review
  · findings (REVIEW-FAIL) → /fold-findings repairs them; a fresh /review-change follows the fold
  · merge gate after REVIEW-PASS → /audit-pr

8. Descope guard

Before creating any issue while executing: classify with the descope test. A descope (moving an acceptance criterion or task out of scope) requires explicit user approval first, then record in the unit doc's ## References section (not a follow-up issue) as: - <YYYY-MM-DD> — descoped: "<criterion>" — approved by user. An issue may never be the first record of a descope.

Required references

These files must be loaded when their topic is active:

• PREFLIGHT.md — all gate blocks (dependency, status, pre-exec, evidence, lint, path-protection)
• EXECUTION_CONTRACT.md — step completion gate, architectural invariants
• PRE_EXECUTION_GATE.md — pre-execution review gate, normalizer order
• FOLDING.md — review finding fold cycle
• DESCOPE.md — descope test and amendment rule
• FORGE_BODY.md — forge operations (gh body-file rule)

Guardrails

Allowed:

• Only the triaged steps listed by the unit doc's Evidence header
• Changes scoped to the acceptance criteria and step tasks
• Documentation updates in the unit doc (Evidence, Progress, References)
• Conventional commit messages per the project's Workflow conventions
• The step's own reference file (read one-hop from the unit doc catalog)

Forbidden:

• Never commit red (test failure) — fix within the step's scope, or record the blocker and stop.
• Never weaken a validator (loosen assertions, reduce coverage) — a repair must keep assertions at least as strong.
• Never execute a step the triage skipped — the catalog is authoritative.
• Never edit the unit doc's Acceptance criteria (that is re-triage with user consent).
• Never expand scope beyond what Non-goals define — findings discovered during implementation never widen the unit.
• Never invent an acceptance criterion — ask the user with concrete options.

Relationship to other skills

unit-lane conducts (triage → steps → doc updates); this executes (one step at a time or all remaining). fold-findings handles review finding repairs. The review pack axes (review-implementation, review-code, review-security, review-perf, review-a11y, review-debt) compose the review step; workflow-status routes here. triage-issue feeds issues into the lane. This skill is the step executor a turn invokes to perform one triaged step of a unit under the full gate machinery.

Portability (agents other than Claude Code)

• No slash menu — open this SKILL.md and follow it literally in a fresh conversation. Where it says run, execute the shell command directly.
• No model tiers — triage and review use the strongest model; execution steps may use cheaper. Never review with a weaker model than the author.
• No /loop/subagents — invoke <NN-slug> for all remaining steps (the built-in loop), or <NN-slug> P<k> for individual steps.
• No fresh workers — execute inline and reduce state to the unit doc after each commit; never re-read prior files.

Done when

• Requested scope is implemented (all remaining steps, one explicit step), gate is green, unit doc Evidence/Progress are current, and the work is committed.
• The closing → Next: block is printed.

Closing recommendation

→ Next: /unit-lane <NN-slug> — the conductor continues with the next triaged step
  · all steps done → /review-change — the mandatory end review
  · findings (REVIEW-FAIL) → /fold-findings repairs them; a fresh /review-change follows the fold
  · merge gate after REVIEW-PASS → /audit-pr — the merge gate