implement-slice

Command: Implement Slice

Implement only the next smallest slice from the plan using TDD.

Arguments

$slice (also available as $ARGUMENTS) optionally names the slice to implement. When empty, take the next pending slice from .claude/scratchpad.md.

Literal-token flag rule: a documented flag is active ONLY if its literal token appears in $ARGUMENTS. In particular, the no-changelog suppression flag is in effect ONLY when the literal token no-changelog was passed. Never infer it from context, and never assume it because the documentation describes it.

Pre-flight Checks

1. Confirm you are NOT on main — must be on a feature branch (feat/* or fix/*)
2. Confirm git status is clean (or explain why not)
3. Parallel subagent mode: when running as a subagent within a parallel wave (wave context provided in spawn prompt), the following rules apply for the entire execution:
   • Do NOT write to .claude/scratchpad.md — the orchestrator handles scratchpad updates
   • Do NOT write to .claude/instincts.md — it is PROTECTED identically to the scratchpad (Section 8 FR-7.2). Track deviation-rule tallies and the build-runner attempts counter in-context instead, and report them to the orchestrator for it to persist (see Step 6, Capture Instincts)
   • Do NOT auto-continue to the next slice — return to the orchestrator after committing
   • Chain git commands: git add <files> && git commit -m '...' as a single Bash command to prevent staging conflicts with sibling subagents
4. Tier-aware documentation check: confirm these documentation files exist — skipped entirely when .claude/scratchpad.md reads ## Tier: quick, since neither file is ever required for a quick-tier change, by design (FR-4.4). This check runs unmodified — exactly as written below — when ## Tier: reads full or the field is absent: absence means full is the backward-compatibility default for every scratchpad written before this tier field existed, so an absent field is never read as license to skip this check.
   • docs/qa/<feature>_test_cases.md — if not, delegate to qa-planner first
   • docs/use-cases/<feature>_use_cases.md — if not, delegate to ba-analyst first
5. Tracer gate: read the plan file and check whether any slice is marked **Tracer:** yes.
   • If a **Tracer:** yes slice exists and this invocation targets a different (non-tracer) slice, AND the tracer slice's Verify: condition has not yet been run and passed: REFUSE. Do not proceed to Step 1 (Identify the Slice) or any TDD work. State plainly that the tracer slice must be implemented and its Verify: condition passed first, name the tracer slice, and instruct the caller to run /implement-slice against the tracer slice before retrying this one. This check exists because standalone invocation of this skill bypasses /develop-feature's wave sequencing entirely — wave ordering alone cannot gate a direct, out-of-band /implement-slice call. Source of truth for "the tracer passed": the tracer slice's DONE record with a commit hash in .claude/scratchpad.md, or a fresh run of the tracer's own Verify: command. If neither is available, or the record is ambiguous, REFUSE — an unverifiable tracer is an unpassed tracer.
   • If this invocation targets the tracer slice itself: proceed normally — the tracer is exempt from its own gate.
   • Exemption (backward compatibility), tier-aware wording (FR-4.5, AC-27): if the plan carries no **Tracer:** yes marker anywhere, this check does not apply. Print the tier-appropriate line verbatim, then continue with the remaining pre-flight checks and TDD flow as normal — the exemption is never silent:
     • When .claude/scratchpad.md reads ## Tier: quick: a marker-free plan here is quick tier's own single-slice plan, exempt from the tracer requirement by design — never a legacy plan. Print exactly: