Architect

Design before implementing. 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. If implementation proves the sketch wrong, throw it out and redesign.

Platform note. On Codex, the Claude tool names, claude-* slugs, and Claude built-in skills named below are Claude defaults. Resolve them via codex-tools.md.

Start

Open a todolist with one entry per phase before starting. Autonomous mode without checkpoints needs the list to show phase position and keep phases from silently disappearing.

1. Ground
2. Sketch
3. Agree
4. Implement
5. Scrap

Phase A: Ground the problem

Build a real mental model of every system the new code touches. Run the how skill over the relevant subsystems. Critique mode if existing structure is the constraint or the design must push back on it.

Naming a file isn't grounding. Produce the traced model how prescribes. If the design redefines ownership or layering, also run 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

Run the arena skill with the design-sketch task and the Phase A grounding artifacts. Pass references/runner-prompt.md as each runner's prompt. Each candidate produces a design package shaped per references/rationale-template.md: the caller's usage written first, then the type sketch, function signatures, module map, and prose rationale derived from it.

Use your configured architect runners (defaults in Models).

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. Reject or revise shallow modules, information leakage, temporal decomposition, and pass-through methods.

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. The synthesis decision populates 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.

The synthesis can ship as its own commit either way. That's the "scaffold first" mode of the foundational-thinking principle skill; subsequent commits read as filling in bodies against a stable contract. Planned and scoped breakage during fill-in is fine, per the outcome-oriented-execution principle skill. For adversarial pressure on the design before implementing, run 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 the sketch are signal worth surfacing, 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. Surface it; don't bolt it on.

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. Surfacing deviations is Phase D's job; a repeated pattern of them is Phase E's trigger.

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. The rewrite signal is repeated friction of the same shape, not single hard cases.

When you scrap:

1. Re-run the how skill over what's been built. The implementation lessons enter the new design as inputs, not vibes.
2. Redesign as if the new constraints had been day-one assumptions, per redesign-from-first-principles.
3. Subtract before adding, per the subtract-before-you-add principle skill. The new sketch should be smaller than the old one before it grows.
4. 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.

Models

Role defaults live in repo-root models.json. /setup-fstack writes a per-harness override sheet that wins at runtime.

• architect runners: claude-opus-5, claude-fable-5, claude-sonnet-5