X_GATE_CODE_UNDOCUMENTED
Means
a code the never-ships list names has no table row, or a code scripts/ declares is missing from that list
Typical cause
the list is a hand-copy of a derived set and nothing read it. checkErrorCodeDocs is satisfied by any `X_*` in backticks anywhere on this page (documentedCodes is one whole-file regex), so being named inside the parenthesis counted as being documented — 20 codes had a name here and no row. From the other side checkErrorCodeRegistry exempts gate codes by scanning scripts/, never by reading the list, so four X_REGISTRY_* codes had rows above Reserved codes that x errors explain refuses
Fix
bun run scripts/gate-codes.ts --json — each finding names the row to write or the code to add to the list