diff --git a/docs/api/blog.md b/docs/api/blog.md
index f12278cf..3535d82c 100644
--- a/docs/api/blog.md
+++ b/docs/api/blog.md
@@ -90,7 +90,14 @@ Get a single blog post by slug.
 ### Path Parameters
 | Param | Type | Description |
 |-------|------|-------------|
-| `slug` | string | URL slug (e.g. `ashnayi-ba-bimari-diabat`) |
+| `slug` | string | URL slug (e.g. `ashnayi-ba-bimari-diabat`) or UUID |
+
+### Query Parameters
+| Param | Type | Required | Description |
+|-------|------|----------|-------------|
+| `city_id` | int | ❌ | Domain scope of the caller. Same rule as `GET /api/v1/blogs?city_id=…`: the post is returned only when it belongs to this city **or** is nationwide (`city IS NULL`). A post owned by another city — including a post assigned to the root record `نوبت 724` (id `600`) — returns **404**. Omit on the main domain (`nobat724.com`) to read any post. |
+
+> بدون این پارامتر، پستی که از لیستِ یک دامنه فیلتر شده بود همچنان با URL مستقیم روی همان دامنه ۲۰۰ می‌گرفت و یک محتوا روی چند دامنه تکرار می‌شد. سایت عمومی (`nobat724_front`) روی دامنه‌های شهری همیشه `city_id` را می‌فرستد.
 
 ### Response `200`
 ```json
@@ -115,7 +122,7 @@ Get a single blog post by slug.
 ### Errors
 | Code | HTTP | Description |
 |------|------|-------------|
-| `ERR_NOT_FOUND_001` | 404 | Blog not found or not published |
+| `ERR_NOT_FOUND_001` | 404 | Blog not found, not published, or owned by another city (when `city_id` is sent) |
 
 ---
 
diff --git a/src/Blog/Controller/BlogController.php b/src/Blog/Controller/BlogController.php
index a8793605..75918bd0 100644
--- a/src/Blog/Controller/BlogController.php
+++ b/src/Blog/Controller/BlogController.php
@@ -115,6 +115,13 @@ class BlogController extends BaseController
                 description: 'Blog slug or UUID',
                 schema: new OA\Schema(type: 'string')
             ),
+            new OA\Parameter(
+                name: 'city_id',
+                in: 'query',
+                required: false,
+                description: 'Domain scope of the caller. A post that belongs to another city is 404 here, exactly as it is absent from GET /api/v1/blogs?city_id=…. Nationwide posts (city IS NULL) are always returned. Omit on the main domain to read any post.',
+                schema: new OA\Schema(type: 'integer')
+            ),
         ],
         responses: [
             new OA\Response(
@@ -133,20 +140,36 @@ class BlogController extends BaseController
                     ]
                 )
             ),
-            new OA\Response(response: 404, description: 'Blog post not found or not published'),
+            new OA\Response(response: 404, description: 'Blog post not found, not published, or owned by another city'),
         ]
     )]
     #[Route('/api/v1/blog/{slug}', methods: ['GET'])]
-    public function detail(string $slug): JsonResponse
+    public function detail(string $slug, Request $request): JsonResponse
     {
         $blog = $this->blogRepo->findBySlug($slug) ?? $this->blogRepo->findByUuid($slug);
         if ($blog === null || $blog->getStatus() !== Blog::STATUS_PUBLISHED) {
             return $this->error(ErrorCodes::ERR_NOT_FOUND_001, 'مقاله یافت نشد', 404);
         }
 
+        // یک پستِ شهریافته فقط روی دامنهٔ خودش وجود دارد. بدون این شرط، پستی که از
+        // لیستِ دامنه حذف شده بود همچنان با URL مستقیم روی هر دامنه‌ای ۲۰۰ می‌گرفت و
+        // همان محتوا روی چند دامنه تکرار می‌شد. پست سراسری (city IS NULL) استثناست.
+        $cityId = $request->query->get('city_id');
+        if ($cityId !== null && $cityId !== '' && !$this->isVisibleOnCity($blog, (int) $cityId)) {
+            return $this->error(ErrorCodes::ERR_NOT_FOUND_001, 'مقاله یافت نشد', 404);
+        }
+
         return $this->success(['data' => $blog->toArray()]);
     }
 
+    /** آینهٔ BlogRepository::applyCityFilter — پست همان شهر یا پست سراسری. */
+    private function isVisibleOnCity(Blog $blog, int $cityId): bool
+    {
+        $owner = $blog->getCity();
+
+        return $owner === null || $owner->getId() === $cityId;
+    }
+
     // ── Admin CRUD ────────────────────────────────────────────────────────────
 
     #[OA\Get(
diff --git a/tests/Blog/BlogCityScopeTest.php b/tests/Blog/BlogCityScopeTest.php
index 75e83438..4a361186 100644
--- a/tests/Blog/BlogCityScopeTest.php
+++ b/tests/Blog/BlogCityScopeTest.php
@@ -108,6 +108,57 @@ class BlogCityScopeTest extends ApiTestCase
         $this->assertNull($natDetail['city']);
     }
 
+    /**
+     * The detail endpoint must scope exactly like the list: a post owned by
+     * another city does not exist on this domain. Without this, a post filtered
+     * out of /api/v1/blogs?city_id=… was still served with a direct URL, so the
+     * same article appeared on every city domain.
+     */
+    public function testDetailIsNotFoundOnAnotherCityDomain(): void
+    {
+        $yasuj  = $this->makeCity('یاسوج');
+        $tabriz = $this->makeCity('تبریز');
+        $post   = $this->makePost('یاسوجی ' . bin2hex(random_bytes(3)), $yasuj);
+        $this->em->flush();
+
+        $this->client->request('GET', '/api/v1/blog/' . $post->getSlug() . '?city_id=' . $tabriz->getId());
+        $this->assertSame(404, $this->responseCode(), 'another city\'s post must not be readable');
+    }
+
+    public function testDetailIsFoundOnItsOwnCityDomain(): void
+    {
+        $yasuj = $this->makeCity('یاسوج');
+        $post  = $this->makePost('یاسوجی ' . bin2hex(random_bytes(3)), $yasuj);
+        $this->em->flush();
+
+        $this->client->request('GET', '/api/v1/blog/' . $post->getUuid() . '?city_id=' . $yasuj->getId());
+        $this->assertSame(200, $this->responseCode());
+    }
+
+    public function testNationwideDetailIsReadableFromEveryCityDomain(): void
+    {
+        $tabriz = $this->makeCity('تبریز');
+        $post   = $this->makePost('سراسری ' . bin2hex(random_bytes(3)), null);
+        $this->em->flush();
+
+        $this->client->request('GET', '/api/v1/blog/' . $post->getSlug() . '?city_id=' . $tabriz->getId());
+        $this->assertSame(200, $this->responseCode(), 'nationwide posts stay visible on city domains');
+    }
+
+    public function testDetailWithoutCityIdStaysUnscoped(): void
+    {
+        $yasuj = $this->makeCity('یاسوج');
+        $post  = $this->makePost('یاسوجی ' . bin2hex(random_bytes(3)), $yasuj);
+        $this->em->flush();
+
+        // The main domain (and any API consumer) omits city_id and sees everything.
+        $this->client->request('GET', '/api/v1/blog/' . $post->getSlug());
+        $this->assertSame(200, $this->responseCode());
+
+        $this->client->request('GET', '/api/v1/blog/' . $post->getSlug() . '?city_id=');
+        $this->assertSame(200, $this->responseCode(), 'an empty city_id must not scope the request');
+    }
+
     public function testAdminCanCreatePostWithAndWithoutCity(): void
     {
         $admin = $this->createUser(['ROLE_ADMIN']);