Slicewise

slicewise

The everyday discipline for building one slice at a time in an existing codebase. You write the code yourself, but every commit unit is objectively verified — a full test gate plus two independent reviewers reconciled against each other — and the human, not the agent, decides what lands.

한국어 안내는 README.ko.md를 참고하세요.

Principles (non-negotiable)

1. No auto-commit. You never run git commit. You hand the user exact, file-disjoint git blocks and they run them, on a fresh branch for the current issue. (Only commit yourself if the user explicitly says "commit it" / "do it".)
2. Always dual review. Every commit unit is reviewed by two independent reviewers in parallel, then reconciled. No risk-based gating — the small unit that "looks trivial" is where the subtle bug hides. If only one reviewer is available, run it and warn that this invariant is relaxed.
3. Tests are the ground truth. A build/compile floor for every unit; the full suite green before anything lands. Risky changes get real integration tests, not mocks or fakes.
4. No scope creep. Only the current issue. Anything outside the plan — extra features, new dependencies, edits to unrelated files — you ask first.

Checklist (make each a todo)

1. Read first, report drift.
2. Plan file-disjoint commit units.
3. Implement → test gate (per unit).
4. Dual review → reconcile (per unit, always).
5. Re-verify → commit handoff.
6. Doc sync + drift sweep.
7. PR / merge unblocking (only if you hit it).

• (cross-cutting) Log reusable troubleshooting the moment you hit it.

Configuration

Read .slicewise.yml (or .json) at the repo root if present; otherwise auto-detect the toolchain from the ecosystem. See docs/configuration.md for the schema and the detect table. The keys you care about: build, test, integration, lint, docs (globs to read in Phase 1), reviewers (the roster for Phase 4), troubleshooting_log, commit_convention. When a key is absent, detect it (package.json→npm, Cargo.toml→cargo, go.mod→go test, pom.xml/build.gradle→mvn/gradle, pyproject.toml→pytest, Makefile→make) and state what you detected so the user can correct you.

Phase 1 — Read first, report drift (before any code)

• Read the configured docs globs (default: docs/**, **/*.md, plus any OpenAPI/schema/ADR files), the related code, and any design notes for this slice. Understand the contract before touching it.
• Drift detection is a first-class deliverable. If two docs disagree, or a doc contradicts the code (a spec that no longer matches the schema, a data model that drifted from the migration), you report it and get a decision before writing code. Silently "fixing" it the wrong way is the classic trap.
• State scope in one line: what you will build, and what is explicitly out of scope.

Phase 2 — Plan file-disjoint commit units

• Split the work into small units whose file sets do not overlap (e.g. infra/port · domain logic · docs). If one file is touched by two units, merge them into one unit.
• For genuinely hard logic (auth/social login, pairing, IoT, RAG, aggregation, external integrations), lay down the skeleton with // TODO(impl) markers and fill it in deliberately — don't fake it.

Phase 3 — Implement → test gate (per unit)

• Write it yourself, matching the surrounding style. Cross-context references go by ID; external systems go through a port/adapter, not a direct call.
• Run the build/compile floor (build command). It must pass — that's the floor, not the goal.
• For risky changes, add real integration tests, not mocks: raw SQL / complex queries, JSONB or document mapping, concurrency and locking, migrations, money, auth/authorization, anything with a data-loss or ownership-boundary failure mode. Assert hard — exercise boundary values, ownership checks, time/ordering — so a false green can't sneak through.
• Before the unit is final, run the full test suite and confirm it is green (failures = 0).

Phase 4 — Dual review → reconcile (per unit, always)

Dispatch the reviewer roster in parallel, in one message. All reviewers are read-only (they report; they never edit). The zero-config default roster is the bundled code-reviewer agent run twice with different lenses:

• Lens A — correctness, security, concurrency / data-safety.
• Lens B — simplicity / DRY, project conventions, test adequacy.

For cross-model diversity, set reviewers: ["codex", "code-reviewer"] in config to use one Codex reviewer (via the codex plugin, if installed) plus one Claude reviewer. If a configured reviewer isn't available, degrade to single and warn that the always-dual-review invariant is relaxed.

Shared prompt template (same for every reviewer, only the lens differs):

• Target: the git diff of the working tree + the list of changed/new file paths + a couple of reference files showing the pattern to match.
• Design context: state the decisions that are already settled, so reviewers check consistency, bugs, and security within that design instead of re-litigating the architecture.
• Output contract: prioritized findings — 🔴 must-fix / 🟡 should-fix / 🟢 nit — each with file:line and a concrete fix. Explicit instruction: "If it's sound, say it's sound. Do not fabricate issues."
• Scrutiny points: data loss, JSONB/serialization mapping, IDOR / authorization, concurrency TOCTOU, migration safety, test adequacy, doc↔code consistency.

Reconcile (this step is the whole point). Compare the two reports; don't just concatenate them. See docs/reconcile-rubric.md for the full decision table. In short:

• 🔴 → verify it's real, then apply, then prove the fix with a new test. If the two reviewers disagree, resolve by evidence, not by vote.
• Over-engineering / speculative asks → reject with a stated reason (name the rejection as explicitly as the adoption). "Deterministic key, so a per-segment HEAD check is unnecessary — rejected."
• Every adopted fix is reflected in code and proven by a test that would fail without it.

Phase 5 — Re-verify → commit handoff

• After applying reconciled fixes, run the test suite again — green.
• Do not commit. Present numbered, file-disjoint blocks:

  git add <exact paths for this unit>
  git commit -m "<conventional subject>" -m "<body>"
  

  Add a trailer (sign-off, issue ref, co-author) only if the project already uses one. The user runs the blocks. If they say "do it", then you run them.

Phase 6 — Doc sync + drift sweep

• If behavior or a contract changed, update the docs it touched (endpoint schemas, error cases, status, ER diagrams, counts/summaries).
• Sweep the mirrors: when you change one field/column, grep for its old name across every doc and generated artifact (overview docs, exported schema JSON, SVG diagrams) so no straggler survives. Mark generated artifacts (SVGs, etc.) for regeneration. Historical changelog lines are history — leave them.

Phase 7 — PR / merge unblocking (only if you hit it)

• Classify the blocker: gh pr view <n> --json mergeable,mergeStateStatus,reviewDecision → CONFLICTING (conflicts) / UNSTABLE or BLOCKED (checks) / review.
• For conflicts: merge origin/<base> in, resolve only the conflicts (union / consistency), confirm zero markers, and get the whole merge tree green before handing off the push.
• For count/summary conflicts, recompute from the underlying groups and reconcile to the true number.

Cross-cutting — Troubleshooting log

When you hit a real troubleshooting trap (build, test, runtime, or a design pitfall), append it to the configured troubleshooting_log (default TROUBLESHOOTING.md). Create it if missing; append to the bottom if it exists — never a fresh file each time. Format each entry as: a one-line title (date + feature/branch), then Cause / Resulting problem / Fix / Alternatives considered. Record only reusable traps, not one-off typos — this is an accumulating asset so the next person doesn't hit the same wall.

Tooling notes

• Reviewers see uncommitted work via git diff (assume a clean baseline before the unit).
• Codex unavailable → single Claude reviewer + a stated note that the full-review invariant is broken.
• build/test/lint and gh run via Bash. Prefer the repo's own scripts over ad-hoc commands.
• If a decision won't show up in a later code scan (a design fork, a rejection rationale, a schema switch), write it down where the project keeps such notes so it isn't lost.