Each contract exposes numeric errors, but contributors and SDK users have no shared reference for interpreting them.
Acceptance criteria:
- Document error names and numeric codes for all four contracts.
- Describe which errors are stable public API and how SDK callers should surface them.
- Add a maintenance note requiring updates when error enums change.
Each contract exposes numeric errors, but contributors and SDK users have no shared reference for interpreting them.
Acceptance criteria: