diff --git a/server/service/post-comments/guest-fields.test.ts b/server/service/post-comments/guest-fields.test.ts
index 601632a..7884a4c 100644
--- a/server/service/post-comments/guest-fields.test.ts
+++ b/server/service/post-comments/guest-fields.test.ts
@@ -32,11 +32,11 @@ describe("resolveGuestFields", () => {
     ).toEqual({ guestEmail: null, guestIsAnonymous: false });
   });
 
-  test("legacy payload without guest email fields falls back to anonymous", () => {
-    expect(
+  test("guest with undefined anonymous flag defaults to non-anonymous and requires email", () => {
+    expect(() =>
       resolveGuestFields({
         viewerPresent: false,
       }),
-    ).toEqual({ guestEmail: null, guestIsAnonymous: true });
+    ).toThrow(GuestCommentValidationError);
   });
 });
diff --git a/server/service/post-comments/guest-fields.ts b/server/service/post-comments/guest-fields.ts
index 57f13fd..3463b72 100644
--- a/server/service/post-comments/guest-fields.ts
+++ b/server/service/post-comments/guest-fields.ts
@@ -14,10 +14,7 @@ export function resolveGuestFields(input: {
     return { guestEmail: null, guestIsAnonymous: false };
   }
 
-  // 兼容过渡策略：旧客户端尚未上送 guestEmail/guestIsAnonymous 时，按匿名处理，避免发布窗口内全量 400。
-  // 待所有客户端完成升级后可移除此分支，恢复严格“默认非匿名且邮箱必填”语义。
-  const isLegacyGuestPayload = input.guestEmail == null && input.guestIsAnonymous === undefined;
-  const guestIsAnonymous = input.guestIsAnonymous === true || isLegacyGuestPayload;
+  const guestIsAnonymous = input.guestIsAnonymous === true;
   const guestEmail = validateGuestCommentEmail(input.guestEmail, guestIsAnonymous);
   return { guestEmail, guestIsAnonymous };
 }