fix(agent): enforce guide-only tool policy (#3088)

tests/test_chat_preprocess_tool_policy.py

@@ -0,0 +1,54 @@
+import pytest
+from types import SimpleNamespace
+
+from src.chat_handler import ChatHandler
+
+
+class _UploadHandler:
+    def resolve_upload(self, *_args, **_kwargs):
+        raise AssertionError("attachments must not be resolved when tool preprocessing is disabled")
+
+    def is_image_file(self, *_args, **_kwargs):
+        raise AssertionError("images must not be inspected when tool preprocessing is disabled")
+
+
+@pytest.mark.asyncio
+async def test_preprocess_can_skip_external_context_and_attachment_work(monkeypatch):
+    async def _fail_transcript(*_args, **_kwargs):
+        raise AssertionError("YouTube transcripts must not be fetched")
+
+    async def _fail_comments(*_args, **_kwargs):
+        raise AssertionError("YouTube comments must not be fetched")
+
+    monkeypatch.setattr("src.chat_handler.extract_transcript_async", _fail_transcript)
+    monkeypatch.setattr("src.chat_handler.fetch_youtube_comments", _fail_comments)
+    monkeypatch.setattr(
+        "src.chat_handler.model_supports_vision",
+        lambda *_args, **_kwargs: (_ for _ in ()).throw(
+            AssertionError("vision support must not be probed")
+        ),
+    )
+
+    handler = ChatHandler(
+        session_manager=None,
+        memory_manager=None,
+        chat_processor=None,
+        research_handler=None,
+        preset_manager=None,
+        upload_handler=_UploadHandler(),
+    )
+    sess = SimpleNamespace(model="text-only", endpoint_url="", owner="user", id="session")
+
+    enhanced, user_content, text_ctx, youtube, attachment_meta = await handler.preprocess_message(
+        "Do not use tools. https://www.youtube.com/watch?v=dQw4w9WgXcQ",
+        ["image-id"],
+        sess,
+        auto_opened_docs=[],
+        allow_tool_preprocessing=False,
+    )
+
+    assert enhanced.startswith("Do not use tools.")
+    assert user_content == enhanced
+    assert text_ctx == enhanced
+    assert youtube == []
+    assert attachment_meta == []