## What & why
We used to enforce the BSD-2-Clause license banner on every source file
via `eslint-plugin-header`. That check was lost when we migrated from
ESLint to Biome (#7033), which has no equivalent rule. This PR
reinstates it as a standalone node script, modelled on the existing
`etc/scripts/check-frontend-imports.js`.
### Why a script rather than a Biome rule
Biome 2.x has no built-in license/header rule and no plugin equivalent
to `eslint-plugin-header`; its experimental GritQL plugins aren't suited
to whole-file-prefix matching. A script needs zero new dependencies and
gives full control over scope and exemptions.
## The check (`etc/scripts/check-license-headers.js`)
A file "has an appropriate banner" if, ignoring an optional shebang, it
opens with a `// Copyright (c) …` line **and** contains the BSD-2-Clause
disclaimer body. The year and copyright holder are intentionally **not**
constrained — the tree legitimately has many holders (Compiler Explorer
Authors, Arm, Microsoft, HRT, individuals). The `(c)`/`(C)` marker is
matched case-insensitively.
**Scope:** `.ts/.js/.mjs/.cjs` under `lib/ static/ shared/ types/ test/
cypress/`.
**Exempt:** generated files (`lib/asm-docs/generated`), vendored
(`docenizer/vendor`), `.d.ts`, and three third-party ports that carry
their own upstream license — `static/ansi-to-html.ts` (MIT),
`lib/node-graceful.ts` (MIT), `shared/rison.ts` (Nanonid/rison port).
**Wired into:** CI (`test-and-deploy.yml`), `npm run check`, the `make
pre-commit` target, the husky pre-commit hook, and `lint-staged` (per
staged file).
Usage:
```
node ./etc/scripts/check-license-headers.js # scan the tracked tree
node ./etc/scripts/check-license-headers.js <files...> # scan specific files (lint-staged)
```
## Backfill
The check surfaced **42 CE-authored files** missing the banner. This PR
backfills them all with the standard `Copyright (c) <year>, Compiler
Explorer Authors` banner, using each file's **git creation year**
(added-at-this-path, so no `--follow` rename artifacts).
## Verification
- `check-license-headers` → clean (was 42 failures)
- `biome check` on all source → no fixes needed (banner format matches
existing convention)
- `tsc` backend + frontend + tests → clean
- pre-commit gauntlet (lint, ts-check, related tests: 528 passed) ran on
commit
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: mattgodbolt-molty <mattgodbolt-molty@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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