lexification-server

Replace the codegen script with `lex build --clear --indexFile --lexicons ../../lexicons`, swap dependencies to `@atproto/lex` and `@atproto/xrpc-server`, delete the gitignored `src/lexicon/` tree, then convert route files one namespace at a time from `server.<ns>.<method>()` to `server.add(schema, …)`.

$isTypeOf reads only the `$type` tag and acts as a TypeScript type predicate, matching the behavior of legacy `isX()` guards. $matches validates the entire value against the schema and is correct for unvalidated data like firehose records or datastore values.

Use `$type` for record and object type strings such as collections and union tags, `$lxm` for XRPC method ids in auth and proxy checks, and `$nsid` for defs documents that define no main type. They can hold identical strings, so a wrong choice type-checks but fails at runtime.

The generated `src/lexicons/` directory is gitignored and does not exist until codegen runs. Run `pnpm run codegen` or a build to generate it; the error means codegen has not run, not that the import path is wrong.

No. Test call sites deliberately keep using `AtpAgent` so tests act as a regression check that the migration did not change behavior. Only test imports of types or constants from the deleted `src/lexicon/` tree must move, either to `../../src/lexicons/index.js` or to legacy equivalents in `@atproto/api`.