Task 4.3: Verify queue API endpoints use key identifier

- Verified queue API endpoints already use 'serie_id' (key) as primary identifier
- Updated test fixtures to use explicit key values (e.g., 'test-series-key')
- Added test to verify queue items include serie_id (key) and serie_folder (metadata)
- Fixed test_queue_items_have_required_fields to find correct item by ID
- Added test_queue_item_uses_key_as_identifier for explicit key verification
- Updated instructions.md to mark Task 4.3 as complete

All 870 tests pass.

tests/api/test_queue_features.py

@@ -45,10 +45,14 @@ async def auth_headers(client: AsyncClient):
 
 @pytest.fixture
 def sample_download_request():
-    """Sample download request for testing."""
+    """Sample download request for testing.
+    
+    Note: serie_id is the primary identifier (key) used for all lookups.
+    serie_folder is metadata only used for filesystem operations.
+    """
     return {
-        "serie_id": "test-series",
-        "serie_folder": "Test Series (2024)",
+        "serie_id": "test-series-key",  # Provider key (primary identifier)
+        "serie_folder": "Test Series (2024)",  # Filesystem folder (metadata)
         "serie_name": "Test Series",
         "episodes": [
             {"season": 1, "episode": 1},
@@ -101,6 +105,11 @@ class TestQueueDisplay:
         )
         assert add_response.status_code == 201
         
+        # Get the added item IDs from response
+        add_data = add_response.json()
+        added_ids = add_data.get("added_items", [])
+        assert len(added_ids) > 0, "No items were added"
+        
         # Get queue status
         response = await client.get(
             "/api/queue/status",
@@ -113,20 +122,83 @@ class TestQueueDisplay:
         pending = data["status"]["pending_queue"]
         
         assert len(pending) > 0
-        item = pending[0]
+        
+        # Find the item we just added by ID
+        item = next((i for i in pending if i["id"] in added_ids), None)
+        assert item is not None, f"Could not find added item in queue. Added IDs: {added_ids}"
         
         # Verify required fields for display
         assert "id" in item
+        assert "serie_id" in item  # Key - primary identifier
+        assert "serie_folder" in item  # Metadata for filesystem ops
         assert "serie_name" in item
         assert "episode" in item
         assert "priority" in item
         assert "added_at" in item
         
+        # Verify serie_id (key) matches what we sent
+        assert item["serie_id"] == sample_download_request["serie_id"]
+        
         # Verify episode structure
         episode = item["episode"]
         assert "season" in episode
         assert "episode" in episode
 
+    @pytest.mark.asyncio
+    async def test_queue_item_uses_key_as_identifier(
+        self, client: AsyncClient, auth_headers: dict
+    ):
+        """Test that queue items use serie_id (key) as primary identifier.
+        
+        Verifies that:
+        - serie_id is the provider-assigned key (URL-safe identifier)
+        - serie_folder is metadata only (not used for identification)
+        - Both fields are present in queue item responses
+        """
+        # Add an item with explicit key and folder
+        request = {
+            "serie_id": "my-test-anime-key",  # Provider key (primary ID)
+            "serie_folder": "My Test Anime (2024)",  # Display name/folder
+            "serie_name": "My Test Anime",
+            "episodes": [{"season": 1, "episode": 1}],
+            "priority": "normal"
+        }
+        
+        add_response = await client.post(
+            "/api/queue/add",
+            json=request,
+            headers=auth_headers
+        )
+        assert add_response.status_code == 201
+        
+        # Get queue status
+        response = await client.get(
+            "/api/queue/status",
+            headers=auth_headers
+        )
+        assert response.status_code == 200
+        
+        data = response.json()
+        pending = data["status"]["pending_queue"]
+        
+        # Find our item by key
+        matching_items = [
+            item for item in pending
+            if item["serie_id"] == "my-test-anime-key"
+        ]
+        assert len(matching_items) >= 1, "Item should be findable by key"
+        
+        item = matching_items[0]
+        
+        # Verify key is used as identifier
+        assert item["serie_id"] == "my-test-anime-key"
+        
+        # Verify folder is preserved as metadata
+        assert item["serie_folder"] == "My Test Anime (2024)"
+        
+        # Verify serie_name is also present
+        assert item["serie_name"] == "My Test Anime"
+
 
 class TestQueueReordering:
     """Test queue reordering functionality."""
@@ -159,9 +231,9 @@ class TestQueueReordering:
             response = await client.post(
                 "/api/queue/add",
                 json={
-                    "serie_id": f"test-{i}",
-                    "serie_folder": f"Test Series {i} (2024)",
-                    "serie_name": f"Test Series {i}",
+                    "serie_id": f"reorder-test-key-{i}",  # Key (primary ID)
+                    "serie_folder": f"Reorder Test {i} (2024)",  # Metadata
+                    "serie_name": f"Reorder Test {i}",
                     "episodes": [{"season": 1, "episode": i+1}],
                     "priority": "normal"
                 },
@@ -414,7 +486,8 @@ class TestBulkOperations:
             add_response = await client.post(
                 "/api/queue/add",
                 json={
-                    "serie_id": f"bulk-test-{i}",
+                    "serie_id": f"bulk-test-key-{i}",  # Key (primary ID)
+                    "serie_folder": f"Bulk Test {i} (2024)",  # Metadata
                     "serie_name": f"Bulk Test {i}",
                     "episodes": [{"season": 1, "episode": i+1}],
                     "priority": "normal"