Use this skill whenever code interacts with the `@atproto/lex` SDK family. This family covers `@atproto/lex` and its companion packages: `@atproto/lex-client`, `@atproto/lex-data`, `@atproto/lex-json`, and `@atproto/lex-schema` (all re-exported by `@atproto/lex`), plus `@atproto/lex-cbor` and `@atproto/xrpc-server` (related companion packages that must be imported directly — they are NOT re-exported by `@atproto/lex`). Trigger on ANY of the following (OR logic — match any one): (1) XRPC calls with `Client`, `xrpc`, or `xrpcSafe`; (2) defining XRPC server routes (`createServer`, `server.add`); (3) validating lexicon-derived data (`$build`, `$matches`, `$isTypeOf`, `$parse`, `$safeParse`, `$validate`); (4) processing AT Protocol data: JSON ↔ Lex with `lexParse` / `lexStringify` / `jsonToLex` / `lexToJson`, or CBOR via the separate `@atproto/lex-cbor` package; (5) installing or building lexicons (`lex install`, `lex build`); (6) working with branded strings (`DidString`, `HandleString`, `AtUriString`, `Cid`, `Da
Testing practices for this monorepo — choosing between unit and end-to-end tests, where test files live, how tsconfig.test.json fits in, how to drive Playwright, to to write/adapt UI/end-to-end tests, and which test runner (vitest vs jest) to use. MUST be invoked BEFORE any code search or file reads whenever the user asks to add, write, or extend a test, add coverage, create a test file, set up testing in a new package, mentions vitest/jest, or refers to an existing `*.test.ts` file. Applies equally to unit tests and to end-to-end / UI tests — the skill routes to a Playwright-MCP-first discovery flow for the latter, which differs from normal code-search workflow.