build — implement spec

Single-thread native plan→execute. You are main Claude. No swarm.

LOAD

1. Read SPEC.md. If missing → tell user to invoke the spec skill first. Stop.
2. Read FORMAT.md once if not loaded.
3. Read §R if present — external facts the build must honor, ⊥ re-derive or contradict.
4. Parse invocation args:
   • §T.n → that task only
   • --next → lowest-numbered row with status . or ~
   • --all or empty → every . row in §T order

High blast radius (shared module, auth, data, money, public §I)? Run /review first. Trivial & reversible? Skip planning ceremony, just do step EXECUTE.

PLAN

Native plan mode — you delegate to it, you do not reinvent task breakdown. For chosen task(s):

1. Cite every §V invariant that applies. Plan must respect all.
2. Cite every §I interface touched. Plan must preserve shape.
3. List files to create / edit.
4. Verification contract — name the EXACT test(s) / acceptance criteria that prove each §V touched. Which test, not "add tests". "Do TDD" alone backfires; the spec says what to check. Each §V touched → a named test that fails first.
5. Name verification command (test, build, lint) — this is the external oracle. Green = done; ⊥ "looks done".

Show plan. Wait for user OK unless auto mode.

EXECUTE

Per task in order:

1. Flip §T.n status cell . → ~. Just write to SPEC.md.
2. Edit code per plan.
3. Run verification command.
4. Pass → flip ~ → x. Next task.
5. Fail → invoke backprop skill. Do NOT retry blindly.

FAIL → BACKPROP

On test/build failure:

1. Read failure output.
2. Ask: is failure (a) my code bug, (b) spec wrong, or (c) unspecified edge case?
3. If (a) → fix code, re-run. No spec change.
4. If (b) or (c) → invoke spec skill with bug: <cause> first, let it update §V and §B, then resume build against updated spec.

Rule: never silently fix root-cause without considering backprop. §B is the memory that stops recurrence.

WRITE POLICY

• Only flip §T status. No other SPEC.md edits from build.
• Other spec edits → invoke spec skill.
• Commit after each §T completes. Message: T<n>: <goal line> + §V cites.

VERIFICATION

Task x only if:

• Verification command (the oracle) exits 0.
• Every §V touched has its named test from the verification contract, and it passes.
• No §V invariant regressed (run full test suite at end).

NON-GOALS

• No sub-agents. No parallel workers. Main thread only.
• No progress dashboards. cat SPEC.md | grep §T is the dashboard.
• No speculative work beyond chosen task scope.