code-decompose

code-decompose (Codex edition)

Steps 4-6 of THE PROCEDURE (~/.codex/AGENTS.md). Entry condition: codebase-first already returned a BUILD gate plus the residual gap. If it hasn't run, run it first — do not re-discover here.

The point: the change must be fully understood before any code is written — the code that exists and the code you intend to write — and that understanding must be written down precisely enough that it could be executed without further judgment. Decomposition is the expensive thinking step; execution is the cheap step done at volume.

Use one bounded Codex builder per unit and a distinct auditor against the same spec when native subagents are available. Never run sibling builders concurrently in a dirty checkout. If subagents are unavailable, preserve the separation in time: finish specing, build, then re-read the diff against the spec with independent-auditor eyes.

Phase 1 — Decompose (write the specs first, no code)

Start from the codebase-first discovery artifact (.scratch/discovery/<slug>.md if present) and carry its REUSE/ADAPT/REJECT verdicts and gate forward verbatim. Then produce:

1. Understanding (3-6 lines): what exists now with file:line anchors, what we want, and the gap. Include the REUSE/ADAPT/REJECT decisions and the STOP/PLAN/BUILD gate. If the gate is STOP or PLAN, output that with its reasoning instead of Units and hand back to Ro.
2. Units — the gap split into the smallest independently-verifiable pieces. Keep splitting until each is mechanical. Each unit is self-contained:

UNIT <n>: <one-line title>
  CONTEXT  — what exists, with file:line. Exactly the code/state you will touch.
  REUSE    — the exact REUSE/ADAPT decisions + source anchors; no invented APIs;
             CHANGE covers only the residual gap.
  CHANGE   — exactly what to write/modify. One correct interpretation only.
  GOAL     — the outcome this unit produces and why.
  VERIFY   — the concrete check that proves this unit is done: the command, the test,
             the expected output, or the file state. Defined BEFORE execution.
  DEPENDS  — which units must land first (this is your execution order).