X_ERROR_CODE_UNTHROWN_STALE
Means
a code UNTHROWN_CODES lists as thrown by nothing is thrown again — delete it from UNTHROWN_CODES in packages/cli/src/unthrown-codes.ts
Typical cause
UNTHROWN_CODES in packages/cli/src/unthrown-codes.ts waives the unthrown check for a code, and shipped source constructs the code again, so the listing would excuse a code that is live
Fix
x errors explain X_ERROR_CODE_UNTHROWN_STALE --json