## What
**ag-cw2y item 4** — the 4th and last new-skill gate that cost
`/burndown` #600 a CI round. A new skill previously tripped
`validate-codex-override-coverage` ("source skill missing from Codex
catalog"). skill-builder now adds the catalog entry automatically.
## How
- **`scripts/append-codex-override-entry.sh`** — idempotent, JSON-aware:
appends a `parity_only` entry
(`name`/`treatment`/`wave=catalog-parity`/`reason`) to
`skills-codex-overrides/catalog.json` if the skill is absent.
`parity_only` is correct for skill-builder's canonical-derived codex
form; author flips to `bespoke` + scaffolds the override dir only if a
Codex-only divergence is needed. Repo-root-injectable.
- **`init.sh`** — calls it in the new-skill plumbing block alongside the
dispositions row (#609/#610) and `--fix-counts` (#610). All three gates
now pre-empted at scaffold time.
## Tests (TDD, red→green)
`tests/scripts/append-codex-override-entry.bats` — appends parity_only /
stays valid JSON / idempotent / no-dup-on-existing. 4/4 green.
shellcheck clean.
## Codex artifact
Refreshed **only skill-builder's** hash (6 unrelated pre-existing `main`
drifts untouched). PR-scope codex validation passes.
## ag-cw2y status after this
Item 1 (#609 check + #610 scaffold) ✅ · Item 2 (#610) ✅ · **Item 4
(here)** ✅ · **Item 3** (codex desc token budget / `ag-vzbt`) is the
only remaining piece. Once item 3 lands, a new skill — and therefore
`ag-hdqu0.8` + `/burndown` #600 — is fully one-shot-green.
Closes-scenario: ag-cw2y#override-catalog-scaffold
Bounded-context: BC4-factory
Evidence: tests/scripts/append-codex-override-entry.bats
Bo