[CI] Verify generated error codes stay in sync with errors.config.ts

[msluszniak]

Problem description

scripts/generate-errors.ts (run via yarn codegen:errors) is the single source of truth for error codes. It reads scripts/errors.config.ts and writes two generated files:

• packages/react-native-executorch/src/errors/ErrorCodes.ts
• packages/react-native-executorch/common/rnexecutorch/ErrorCodes.h

.github/workflows/ci.yml runs only lint, typecheck, and build-library. Nothing verifies that the committed generated files actually match errors.config.ts. A contributor who edits errors.config.ts (or hand-edits a generated file) without rerunning codegen will commit sources that silently disagree.

Because the same numeric codes cross the JSI boundary, drift is not cosmetic: a code thrown from C++ can resolve to a different name — or to no enum member — on the TS side. This exact failure mode is already documented in the RnExecutorchError class doc comment in src/errors/errorUtils.ts, which notes codes "flow through as a raw number" when the generated files drift.

Proposed solution

Add a CI step (cheapest to fold into the existing lint job — no native build needed) that regenerates and diffs:

- name: Verify error codes are up to date
  run: |
    yarn codegen:errors
    git diff --exit-code -- \
      packages/react-native-executorch/src/errors/ErrorCodes.ts \
      packages/react-native-executorch/common/rnexecutorch/ErrorCodes.h \
      || { echo "::error::Error codes are stale. Run 'yarn codegen:errors' and commit the result."; exit 1; }

Alternative solutions

A lefthook pre-commit hook could regenerate + stage automatically, but it's bypassable with --no-verify and does nothing for changes made via the GitHub web UI or introduced during a rebase. CI is the authoritative gate; a hook is a complementary convenience, not a replacement.

Benefits to React Native ExecuTorch

Guarantees the C++/TS error-code contract cannot silently diverge, protecting the error-handling path every module depends on. Effectively free (TS-only, no emulator/native toolchain).

Additional context

Generated outputs and their writer are at scripts/generate-errors.ts:84-117. Root script: codegen:errors in the top-level package.json.