CI does not run format:check; 23 files are Prettier-dirty

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.github/workflows/tests.yml runs type-check, lint, npm run verify, the unit suite and a production build — but not npm run format:check.

This was deliberate and is recorded in §14 2026-07-18 (m):

format:check is deliberately omitted until the 25 pre-existing Prettier-dirty files are fixed, so CI is not born red.

The count is now 23 files (npx prettier --check .), so the debt is real and roughly static. Until the step is enabled, formatting drift is unpoliced and the gap will keep growing.

Scope

1. One formatting-only commit: npm run format, no functional edits, so the diff stays reviewable and never mixes with behaviour changes.
2. Add the format:check step to tests.yml in the same pull request, so the debt cannot silently return.

Worth doing as its own pull request rather than alongside a feature, since it will touch a large number of files.

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Landed on main in 1396f3b.

The backlog had drifted from the 23 files in the issue body to 35 by the time this was picked up — the drift argument making its own case. npm run format fixes all 35, and format:check now runs in the quality job of tests.yml after verify.

One thing worth recording, because it means this was not purely mechanical: eslint.config.js re-asserts curly: ['error', 'multi-line'] after eslint-config-prettier disables it, so a braceless if body is legal on one line but not once wrapped. Six long bodies in browser-smoke.mjs, inserts/effects.ts and GridCanvas.tsx were under the print width only because they were unformatted; Prettier wrapped them and curly then rejected all six. They took braces, which satisfies both tools — relaxing the rule would have settled it the wrong way. This is also why the reformat and the CI step had to land in one commit: either half alone leaves the tree failing the other check.

Removed the testing label — no spec §11 verification work happened here; it is CI/tooling, which github already covers.

type-check, lint, npm run verify, format:check, 1014 unit tests and the production build all pass. Spec §14 2026-07-18 (ab) records it.