symfony-code-contributionlisted

## When to Activate Use when writing, modifying, or reviewing **PHP** code for a contribution to Symfony core or any Symfony-maintained PHP package (bundles, UX PHP side, AI, Mailer, Messenger, Recipes' PHP, etc.). Do **not** apply these rules to JavaScript/TypeScript projects such as **Webpack Encore** or the Stimulus/UX frontend assets — follow that project's own `CONTRIBUTING` and standards instead. For documentation (`.rst`) changes, use the `symfony-docs-contribution` skill. ## Core Rules 1. **Run PHP CS Fixer before every commit.** Most style below is auto-enforced by the project's `.php-cs-fixer.dist.php` — never hand-format against it: `php ./vendor/bin/php-cs-fixer fix -v`. 2. **Never break the backward-compatibility promise on a maintenance/minor branch.** Public and protected APIs are frozen: deprecate, never remove or change signatures. Breaking changes land only on the next major branch. 3. **Target the right branch.** Bug fixes -> oldest maintained branch that still has the bug (it merges up automatically). New features and deprecations -> current development branch. Never add a feature on a patch branch. 4. **Ship every deprecation complete, in the same PR:** a `trigger_deprecation()` call, an `@deprecated` PHPDoc tag, a `CHANGELOG.md` entry, and the `UPGRADE-*.md` entries. 5. **Add the MIT license header** at the top of every new PHP file, before the `namespace`. 6. **One class per file. Add tests.** Do not write PHPDoc that only restates the signature. #