X_ERROR_CODE_UNTHROWN
Means
a registered error code is constructed by nothing and UNTHROWN_CODES in packages/cli/src/unthrown-codes.ts does not list it
Typical cause
a code is registered and this page presents it as live, but no shipped source constructs it, so a reader matching on it waits for an error that cannot arrive. The waiver is a list, UNTHROWN_CODES in packages/cli/src/unthrown-codes.ts, or the code's place under Reserved codes — a row's wording waives nothing. Add the code to UNTHROWN_CODES and write "registered, thrown by nothing since <version>" into its row, naming the code that replaced it — or throw it again where it belongs. Never delete the registration: a shipped code never changes meaning
Fix
x errors explain X_ERROR_CODE_UNTHROWN --json