test(ai): guard prompt max on the editor endpoint and the wizard min boundary

- Assert GeneratePostContentRequest rejects a prompt over the shared max, so the
  editor's limit is pinned explicitly (not only implied by the create wizard).
- Assert the create wizard accepts a prompt at exactly the minimum length,
  complementing the below-minimum rejection.

tests/Feature/Ai/PostAiCreateTest.php

@@ -44,6 +44,19 @@
     Bus::assertNotDispatched(StreamPostCreation::class);
 });
 
+test('start accepts a prompt at the minimum length', function () {
+    Bus::fake();
+
+    $this->actingAs($this->user)
+        ->postJson(route('app.posts.ai.create'), [
+            'prompt' => str_repeat('a', AiPromptRules::PROMPT_MIN_LENGTH),
+            'format' => 'x_post',
+        ])
+        ->assertStatus(Response::HTTP_ACCEPTED);
+
+    Bus::assertDispatched(StreamPostCreation::class);
+});
+
 test('start rejects a prompt longer than the maximum length', function () {
     Bus::fake();
 

tests/Feature/Ai/PostAiGenerateTest.php

@@ -7,6 +7,7 @@
 use App\Models\Post;
 use App\Models\User;
 use App\Models\Workspace;
+use App\Support\AiPromptRules;
 use Illuminate\Support\Facades\Bus;
 use Symfony\Component\HttpFoundation\Response;
 
@@ -34,6 +35,19 @@
         ->assertJsonValidationErrors(['prompt']);
 });
 
+test('endpoint rejects a prompt longer than the maximum length', function () {
+    Bus::fake();
+
+    $this->actingAs($this->user)
+        ->postJson(route('app.posts.ai.generate', $this->post), [
+            'prompt' => str_repeat('a', AiPromptRules::PROMPT_MAX_LENGTH + 1),
+        ])
+        ->assertStatus(Response::HTTP_UNPROCESSABLE_ENTITY)
+        ->assertJsonValidationErrors(['prompt']);
+
+    Bus::assertNotDispatched(StreamPostContent::class);
+});
+
 test('endpoint blocks access to other workspace posts', function () {
     Bus::fake();
     $otherWorkspace = Workspace::factory()->create();