typescript-error-code-mapping

Answer

The SDK harness errorResponse() hardcoded INTERNAL_ERROR for every status code, so a 400 arrived as INTERNAL_ERROR instead of the documented INVALID_REQUEST. Fix = a union-keyed STATUS_TO_ERROR_CODE map + deriving the code from it, plus flipping the test assertion that had codified the bug.

src/error-codes.ts — the map, keyed by the HttpStatusCode union type (exhaustive at compile time):

export type HttpStatusCode = 400 | 404 | 500;
export type SdkErrorCode = "INVALID_REQUEST" | "SESSION_NOT_FOUND" | "INTERNAL_ERROR";

export const STATUS_TO_ERROR_CODE: Record<HttpStatusCode, SdkErrorCode> = {
    400: "INVALID_REQUEST",
    404: "SESSION_NOT_FOUND",
    500: "INTERNAL_ERROR",
};
export const DEFAULT_ERROR_CODE: SdkErrorCode = "INTERNAL_ERROR";

src/harness.ts — the errorResponse() fix:

// BEFORE (bug): code was hardcoded, so every status returned INTERNAL_ERROR
//   return { statusCode, body: { error: { code: "INTERNAL_ERROR", message } } };

// AFTER (fix): code is derived from the union-keyed map (undefined-safe)
export function errorResponse(statusCode: HttpStatusCode, message: string): ErrorResponse {
    return {
        statusCode,
        body: {
            error: {
                code: STATUS_TO_ERROR_CODE[statusCode] ?? DEFAULT_ERROR_CODE,
                message,
            },
        },
    };
}

test/error-response.test.ts — the flipped assertion (was INTERNAL_ERROR for all codes, now asserts the documented mapping):

it.each<[HttpStatusCode, SdkErrorCode]>([
    [400, "INVALID_REQUEST"],
    [404, "SESSION_NOT_FOUND"],
    [500, "INTERNAL_ERROR"],
])("maps HTTP %i to %s", (statusCode, expectedCode) => {
    const response = errorResponse(statusCode, `request failed with ${statusCode}`);
    expect(response.statusCode).toBe(statusCode);
    expect(response.body.error.code).toBe(expectedCode);
});