diff --git a/services/cards-server/src/lib/errors.ts b/services/cards-server/src/lib/errors.ts
index cb4a26aee..f013b358e 100644
--- a/services/cards-server/src/lib/errors.ts
+++ b/services/cards-server/src/lib/errors.ts
@@ -1,51 +1,63 @@
 /**
- * Domain errors — caught by serviceErrorHandler from @mana/shared-hono
- * and translated to JSON responses with the right status code.
+ * Domain errors — caught by `serviceErrorHandler` from @mana/shared-hono.
+ *
+ * The shared handler only translates Hono `HTTPException`s; anything
+ * else degrades to 500. So our errors extend HTTPException directly
+ * rather than maintaining a parallel hierarchy.
+ *
+ * `details` (e.g. zod issue tree) is passed via `cause` because the
+ * shared handler picks that up and surfaces it in the JSON body.
  */
 
-export class HttpError extends Error {
-	constructor(
-		public status: number,
-		message: string,
-		public code?: string,
-		public details?: unknown
-	) {
-		super(message);
-		this.name = 'HttpError';
-	}
+import { HTTPException } from 'hono/http-exception';
+import type { ContentfulStatusCode } from 'hono/utils/http-status';
+
+function makeException(
+	status: ContentfulStatusCode,
+	message: string,
+	code?: string,
+	details?: unknown
+) {
+	return new HTTPException(status, {
+		message,
+		cause: details ? { code, details } : code ? { code } : undefined,
+	});
 }
 
-export class UnauthorizedError extends HttpError {
+export class HttpError extends HTTPException {}
+
+export class UnauthorizedError extends HTTPException {
 	constructor(message = 'Unauthorized') {
-		super(401, message, 'unauthorized');
-		this.name = 'UnauthorizedError';
+		super(401, { message, cause: { code: 'unauthorized' } });
 	}
 }
 
-export class ForbiddenError extends HttpError {
+export class ForbiddenError extends HTTPException {
 	constructor(message = 'Forbidden') {
-		super(403, message, 'forbidden');
-		this.name = 'ForbiddenError';
+		super(403, { message, cause: { code: 'forbidden' } });
 	}
 }
 
-export class NotFoundError extends HttpError {
+export class NotFoundError extends HTTPException {
 	constructor(message = 'Not found') {
-		super(404, message, 'not_found');
-		this.name = 'NotFoundError';
+		super(404, { message, cause: { code: 'not_found' } });
 	}
 }
 
-export class ConflictError extends HttpError {
+export class ConflictError extends HTTPException {
 	constructor(message = 'Conflict') {
-		super(409, message, 'conflict');
-		this.name = 'ConflictError';
+		super(409, { message, cause: { code: 'conflict' } });
 	}
 }
 
-export class BadRequestError extends HttpError {
+export class BadRequestError extends HTTPException {
 	constructor(message = 'Bad request', details?: unknown) {
-		super(400, message, 'bad_request', details);
-		this.name = 'BadRequestError';
+		super(400, {
+			message,
+			cause: details ? { code: 'bad_request', details } : { code: 'bad_request' },
+		});
 	}
 }
+
+// Keep makeException exported in case future code wants the raw factory.
+export { makeException };