X_CONTRACT_DRIFT
Means
client and server disagree about the contract
Typical cause
three raises. Build id: the typed client holds types from one build and a server on another answered (rpc({ buildId }) against the x-ultimate-build response header). Path style: a POST reached the path an action has under a pathStyle this server does not serve — 404, the cause names the action, both styles and the served path (As of 2026-10; it was a bare X_ROUTE_NOT_FOUND). Contract test: a generated contract assertion did not hold — the OpenAPI document has no entry for the action, or its policy denial could not be proven
Fix
build id: reload the page. Path style: rpc<Api['actions']>({ baseUrl, pathStyle: 'readable' }) with the style the cause names — a browser passes none, the page states it. Contract test: the thrown fix: names the edit; x actions show <name> --json prints the schema