revert(api): drop generated-API handler guard from this PR

The deprecated ErrorResponseHandlerForGeneratedAPIs guard broke toAPIError's
defaultMessage fallback (which relied on the handler crashing), regressing the
error UX in ServiceAccount/Roles screens. Moved to a stacked PR + tracked in
engineering-pod#5761. Keeps this PR scoped to ErrorResponseHandlerV2 +
convertToApiError, and the strengthened V2 handler tests remain.

frontend/src/api/ErrorResponseHandlerForGeneratedAPIs.ts

@@ -62,9 +62,7 @@ export function convertToApiError(
 	return new APIError({
 		httpStatusCode: response?.status || error.status || 500,
 		error: {
-			code:
-				errorData?.code ||
-				String(response?.status || error.code || 'unknown_error'),
+			code: errorData?.code || 'UPSTREAM_UNAVAILABLE',
 			message:
 				errorData?.message ||
 				response?.statusText ||

frontend/src/api/ErrorResponseHandlerV2.ts

@@ -2,19 +2,38 @@ import { AxiosError } from 'axios';
 import { ErrorV2Resp } from 'types/api';
 import APIError from 'types/api/error';
 
+function isErrorV2Resp(data: unknown): data is ErrorV2Resp {
+	return (
+		typeof data === 'object' &&
+		data !== null &&
+		'error' in data &&
+		typeof (data as ErrorV2Resp).error?.code === 'string'
+	);
+}
+
 // reference - https://axios-http.com/docs/handling_errors
 export function ErrorResponseHandlerV2(error: AxiosError<ErrorV2Resp>): never {
 	const { response, request } = error;
 	// The request was made and the server responded with a status code
 	// that falls out of the range of 2xx
 	if (response) {
+		// response.data isn't guaranteed to be a V2 envelope (e.g. a gateway 5xx
+		// with an HTML/empty body during a deploy), so verify the shape first.
+		const data: unknown = response.data;
+		if (isErrorV2Resp(data)) {
+			const { code, message, url, errors } = data.error;
+			throw new APIError({
+				httpStatusCode: response.status || 500,
+				error: { code, message, url, errors },
+			});
+		}
 		throw new APIError({
 			httpStatusCode: response.status || 500,
 			error: {
-				code: response.data.error.code,
-				message: response.data.error.message,
-				url: response.data.error.url,
-				errors: response.data.error.errors,
+				code: 'UPSTREAM_UNAVAILABLE',
+				message: error.message || 'Something went wrong',
+				url: '',
+				errors: [],
 			},
 		});
 	}

frontend/src/api/__tests__/ErrorResponseHandlerV2.test.ts

@@ -0,0 +1,126 @@
+import { ErrorResponseHandlerV2 } from 'api/ErrorResponseHandlerV2';
+import { AxiosError } from 'axios';
+import { ErrorV2Resp } from 'types/api';
+import APIError from 'types/api/error';
+
+function asAxiosError(partial: Partial<AxiosError>): AxiosError<ErrorV2Resp> {
+	return partial as AxiosError<ErrorV2Resp>;
+}
+
+// ErrorResponseHandlerV2 always throws — capture the APIError so assertions stay
+// unconditional.
+function runHandler(error: AxiosError<ErrorV2Resp>): APIError {
+	try {
+		ErrorResponseHandlerV2(error);
+	} catch (thrown) {
+		return thrown as APIError;
+	}
+	throw new Error('expected ErrorResponseHandlerV2 to throw');
+}
+
+type ExpectedError = {
+	httpStatusCode: number;
+	code: string;
+	message: string;
+	errors: { message: string }[];
+};
+
+// One row per response shape the handler must normalize. New shapes (with
+// different bodies) can be added here without a new test block.
+const cases: {
+	name: string;
+	error: AxiosError<ErrorV2Resp>;
+	expected: ExpectedError;
+}[] = [
+	{
+		name: 'well-formed V2 error envelope',
+		error: asAxiosError({
+			message: 'Request failed with status code 400',
+			response: {
+				status: 400,
+				data: {
+					error: {
+						code: 'bad_request',
+						message: 'Invalid dashboard payload',
+						url: 'https://signoz.io/docs',
+						errors: [{ message: 'name is required' }, { message: 'name too long' }],
+					},
+				},
+			} as AxiosError['response'],
+		}),
+		expected: {
+			httpStatusCode: 400,
+			code: 'bad_request',
+			message: 'Invalid dashboard payload',
+			errors: [{ message: 'name is required' }, { message: 'name too long' }],
+		},
+	},
+	{
+		// Regression: during a deployment the gateway returns a 5xx with a
+		// non-envelope body. Reading response.data.error.code used to throw a
+		// TypeError from inside the handler itself. See engineering-pod#5760.
+		name: '5xx with a non-envelope HTML body',
+		error: asAxiosError({
+			message: 'Request failed with status code 503',
+			response: {
+				status: 503,
+				data: '<html><body>503 Service Temporarily Unavailable</body></html>',
+			} as AxiosError['response'],
+		}),
+		expected: {
+			httpStatusCode: 503,
+			code: 'UPSTREAM_UNAVAILABLE',
+			message: 'Request failed with status code 503',
+			errors: [],
+		},
+	},
+	{
+		name: '5xx with an empty body',
+		error: asAxiosError({
+			message: 'Request failed with status code 502',
+			response: {
+				status: 502,
+				data: undefined,
+			} as AxiosError['response'],
+		}),
+		expected: {
+			httpStatusCode: 502,
+			code: 'UPSTREAM_UNAVAILABLE',
+			message: 'Request failed with status code 502',
+			errors: [],
+		},
+	},
+	{
+		name: 'no response received (network error)',
+		error: asAxiosError({
+			message: 'Network Error',
+			code: 'ERR_NETWORK',
+			name: 'AxiosError',
+			request: {},
+		}),
+		expected: {
+			httpStatusCode: 500,
+			code: 'ERR_NETWORK',
+			message: 'Network Error',
+			errors: [],
+		},
+	},
+];
+
+describe('ErrorResponseHandlerV2', () => {
+	it.each(cases)(
+		'normalizes $name into a consistent APIError',
+		({ error, expected }) => {
+			const apiError = runHandler(error);
+
+			expect(apiError).toBeInstanceOf(APIError);
+			expect(apiError.getHttpStatusCode()).toBe(expected.httpStatusCode);
+			expect(apiError.getErrorCode()).toBe(expected.code);
+			expect(apiError.getErrorMessage()).toBe(expected.message);
+			// The sub-error messages feed several parts of the UI, so assert them.
+			expect(apiError.getErrorDetails().error.errors).toStrictEqual(
+				expected.errors,
+			);
+		},
+	);
+});

frontend/src/pages/DashboardPageV2/DashboardContainer/PanelsAndSectionsLayout/Panel/PanelStatus/__tests__/utils.test.ts

@@ -1,6 +1,8 @@
-import type { RenderErrorResponseDTO } from 'api/generated/services/sigNoz.schemas';
+import type {
+	Querybuildertypesv5QueryWarnDataDTO as WarningDTO,
+	RenderErrorResponseDTO,
+} from 'api/generated/services/sigNoz.schemas';
 import type { AxiosError } from 'axios';
-import type { Querybuildertypesv5QueryWarnDataDTO as WarningDTO } from 'api/generated/services/sigNoz.schemas';
 import { StatusCodes } from 'http-status-codes';
 
 import { panelStatusFromError, panelStatusFromWarning } from '../utils';
@@ -44,7 +46,7 @@ describe('panelStatusFromError', () => {
 
 	it('falls back to the error message when there is no structured body', () => {
 		expect(panelStatusFromError(new Error('boom'))).toStrictEqual({
-			code: 'unknown_error',
+			code: 'UPSTREAM_UNAVAILABLE',
 			message: 'boom',
 			docsUrl: undefined,
 			messages: [],