Sketch types, function signatures, class shapes, and module boundaries with not implemented bodies and pseudocode. Synthesize across multiple model perspectives, then fill in code against the chosen sketch.
Start
Open a worklist with one entry per phase before starting.
- Ground
- Sketch
- Agree
- Implement
- Scrap
Phase A: Ground the problem
Build a real mental model of every system the new code touches. Use the how skill on the relevant subsystems.
Naming a file isn't grounding. Produce the architectural explanation how prescribes. If the design redefines ownership or layering, also use the why skill on the existing shape so the rationale becomes a constraint, not a guess.
Skip Phase A only when the work is genuinely greenfield with no surrounding system to integrate.
Phase B: Sketch
Use the arena skill with the design-sketch task and the Phase A grounding artifacts. Pass references/runner-prompt.md as each runner's prompt.
Take the runners from the architect runners role in place of arena runners. Its default is fable, opus, sonnet. Alias and rejected entries follow the runner rules in the arena skill's Phase A. Use the pstack-harness skill for the spawn. Its Spawn a role section resolves the role and builds this CLI's spawn call.
Design it twice. Require at least two structurally distinct candidates before synthesis, even when the first looks sufficient. This is the exhaust-the-design-space principle skill made concrete. Whole-shape alternatives, not point fixes inside one shape.
Screen every candidate against references/design-red-flags.md before synthesis. Assume the next contributor is an agent that sees only the files it opened, copies the nearest example, and takes the shortest path that compiles. Prefer the design where a change that looks right from one file is right for the whole repo.
Compare viable candidates on interface depth. Prefer the design that hides more complexity behind a smaller, simpler public surface. A rich interface can keep call chains short by concentrating capability instead of scattering it across layers.
Arena returns one synthesized design package. Its synthesis decision fills the rationale's "Synthesis decision" section.
Phase C: Agree (opt-in)
Default: proceed directly to implementation with the synthesized design. No human checkpoint.
Opt in to a checkpoint when the invoker explicitly asks: "/architect with checkpoint," "stop and show me before implementing," or similar. Then surface the synthesized design and pause for sign-off.
Without a checkpoint, or once the invoker signs off, the synthesis can ship as its own commit, as the "scaffold first" mode of the foundational-thinking principle skill. Planned and scoped breakage during fill-in is fine, per the outcome-oriented-execution principle skill. For adversarial pressure on the design before implementing, use the interrogate skill on the synthesized sketch.
If the human pushes back on the shape (in a checkpoint or after the fact), treat that as Phase A evidence. Re-ground and re-run Phase B before writing more code.
Phase D: Implement against the sketch
Replace not implemented bodies with code, pseudocode with logic. The synthesized sketch is the contract. Deviations from it are signal to surface, not friction to absorb silently. If a function needs a parameter the sketch didn't anticipate, ask whether the sketch was wrong, the requirement was missed, or the implementation is overreaching.
Phase E: Scrap when the architecture is wrong
If implementation keeps producing friction the sketch can't absorb, throw the sketch out. Don't bolt fixes onto a wrong design, per the redesign-from-first-principles and fix-root-causes principle skills.
The signal is a pattern, not single instances. Tells:
- The same shape of workaround appearing repeatedly across unrelated code.
- Multiple unrelated edge cases that all need special-case branches.
- Types that need escape hatches (
any, casts, optional fields always set in practice) to compile. - The "we need a lock" reflex when the sketch said the state wasn't shared.
- Callers having to know the abstraction's internal rules to use it.
- Two or more independent Phase D deviations of the same shape across the implementation.
Use judgment. A few edge cases don't condemn an architecture. Some problems are legitimately complex. Complexity in the data is not complexity in the design.
When you scrap:
- Use the how skill again on what's been built.
- Redesign as if the new constraints had been day-one assumptions, per redesign-from-first-principles.
- Subtract before adding, per the subtract-before-you-add principle skill. The new sketch should be smaller than the old one before it grows.
- Return to Phase B and re-run arena.
Outputs
The caller's usage is written first and the type sketch derived from it. One file with new types and signatures for small changes. Module map plus type definitions for larger work. The rationale ships alongside, shaped per references/rationale-template.md, including the usage sketch and the synthesis decision.