Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="tests/unit/test_astr_main_agent.py" line_range="345-360" />
<code_context>

         assert req.system_prompt == "System"

+    @pytest.mark.asyncio
+    @pytest.mark.parametrize("prompt", ["", "   \n\t"])
+    async def test_apply_kb_blank_prompt(self, prompt, mock_event, mock_context):
+        """Test applying knowledge base when prompt is blank."""
+        module = ama
+        req = ProviderRequest(prompt=prompt, system_prompt="System")
+        config = module.MainAgentBuildConfig(
+            tool_call_timeout=60, kb_agentic_mode=False
+        )
+        retrieve = AsyncMock(return_value="KB result")
+
+        with patch("astrbot.core.astr_main_agent.retrieve_knowledge_base", retrieve):
+            await module._apply_kb(mock_event, req, mock_context, config)
+
+        retrieve.assert_not_awaited()
+        assert req.system_prompt == "System"
+
     @pytest.mark.asyncio
</code_context>
<issue_to_address>
**suggestion (testing):** Add a test case for prompts with surrounding whitespace that should still trigger KB retrieval

To fully exercise the new `strip()` condition, please add a case like `"  hello  "` where the prompt is non-empty after stripping. That test should assert `retrieve_knowledge_base` is awaited and receives the original prompt, confirming we don’t skip retrieval when only leading/trailing whitespace is present.

```suggestion
    @pytest.mark.asyncio
    @pytest.mark.parametrize("prompt", ["", "   \n\t"])
    async def test_apply_kb_blank_prompt(self, prompt, mock_event, mock_context):
        """Test applying knowledge base when prompt is blank."""
        module = ama
        req = ProviderRequest(prompt=prompt, system_prompt="System")
        config = module.MainAgentBuildConfig(
            tool_call_timeout=60, kb_agentic_mode=False
        )
        retrieve = AsyncMock(return_value="KB result")

        with patch("astrbot.core.astr_main_agent.retrieve_knowledge_base", retrieve):
            await module._apply_kb(mock_event, req, mock_context, config)

        retrieve.assert_not_awaited()
        assert req.system_prompt == "System"

    @pytest.mark.asyncio
    async def test_apply_kb_prompt_with_surrounding_whitespace(
        self, mock_event, mock_context
    ):
        """Test applying knowledge base when prompt has surrounding whitespace but is non-empty."""
        module = ama
        prompt = "  hello  "
        req = ProviderRequest(prompt=prompt, system_prompt="System")
        config = module.MainAgentBuildConfig(
            tool_call_timeout=60, kb_agentic_mode=False
        )
        retrieve = AsyncMock(return_value="KB result")

        with patch("astrbot.core.astr_main_agent.retrieve_knowledge_base", retrieve):
            await module._apply_kb(mock_event, req, mock_context, config)

        retrieve.assert_awaited_once_with(mock_event, req, mock_context, config)
        # Ensure we passed the original prompt object through to retrieval
        assert req.prompt == prompt
```
</issue_to_address>