Implement Slice

Implement Slice

Executes a single slice with unit tests and a post-implementation Reflect step. Agent-first: invoked by the slice-implementer subagent under the parent orchestrator (implement-mainspec). No human prompts.

Invocation Contract

This skill is invoked by the slice-implementer subagent, not directly by the harness dispatcher. The subagent's prompt provides:

Inputs:

• slice_path — absolute path to the slice file (may be outside the working directory).
• working_directory — absolute path to the feature branch checkout (repo root).

Outputs (uncommitted, in the working directory):

• Implemented code matching the slice's specification.
• Unit tests created/updated.
• Optional: edits under .claude/skills/expert/references/ if Reflect produced a high-bar update.

The parent orchestrator (implement-mainspec) handles git (add, commit, push) after this skill exits. Do NOT commit, do NOT run git operations, do NOT create PRs.

Result reporting (to the calling subagent):

• SUCCESS: list key files changed, tests passing, Reflect outcome (no-op | add | edit | delete).
• FAILURE: describe what went wrong. Reasons include: test_failure (unit tests red), implementation_blocked (spec contradicts the codebase).

Workflow

1. Read slice - Load the entire slice file into context.
2. Create TODO list - Three items:
   • {slice-name} - Implement
   • {slice-name} - Unit Tests
   • {slice-name} - Reflect
3. Implement - Mark in_progress, implement all code specified in the slice.
4. Unit tests - Create/update unit tests for the implemented functionality. All tests must pass before proceeding.
5. Reflect - See the Reflection Protocol below.
6. Complete - Mark all TODOs complete, stop.

The working directory is the feature branch checkout. There should be no prior partial state to resume from — work as if the slate is clean.

Reflection Protocol

Run only after Implement + Unit Tests are green.

Step A — Load long-term memory

Invoke /expert so the skill body and its reference files are pulled into your context:

skill: "expert"

If absent, Reflect is a no-op. Never fail the slice on missing /expert.

Otherwise, read the reference files that overlap with what this slice touched (architecture area, patterns used, file types modified).

Step B — Judge: add, edit, delete, or no-op

You now hold two things:

1. Your experience implementing this slice — what was confusing, what pattern you implemented, where the spec contradicted the actual codebase (already in your context window).
2. The current long-term memory — what /expert says about those areas (loaded in Step A).

High bar — default to no-op unless you have a strong reason to add, edit, or delete. Use the following table to guide your decision:

Strong signals to act: slice got stuck for many iterations, or the slice spec explicitly contradicted code that already exists. Small deviations are noise — prefer NO-OP.

Step C — Apply directly (only for add/edit/delete)

• Write the change to .claude/skills/expert/references/.
• If you added or deleted a reference file, update .claude/skills/expert/SKILL.md's one-line index.
• Do NOT touch AGENTS.md — that is owned by /learn post-merge.
• The orchestrator commits these Expert-file changes with the slice and has full authority to resolve any resulting merge conflicts.

TODO Structure

[ ] 1.3-user-auth - Implement
[ ] 1.3-user-auth - Unit Tests
[ ] 1.3-user-auth - Reflect

Guidelines

DON'T:

• Use AskUserQuestion. No human is in the loop.
• Implement beyond the slice scope.
• Proceed with failing unit tests.
• Implement dependent slices (that's for implement-mainspec).
• Run git commands or create PRs — the parent orchestrator handles git.
• Fail the slice because /expert is unavailable or Reflect produced no update.