fix(crawl4ai): report a format error for non-object 200 payloads (#7065)

Crawl4AI's client assumed a JSON 200 was an object and indexed it. A reverse
proxy, a version-skewed server or an error document delivered with HTTP 200
can return a list or a bare scalar instead, and then:

- `data.get(...)` raised "'list' object has no attribute 'get'", and the
  generic handler echoed that Python text to the agent;
- a non-string `markdown` field reached `.strip()` and raised the same way
  one level in (["# heading"], 123, {"text": ...}).

Both now report "Crawl4AI returned an unexpected response format" and log
the unexpected type. This matches the sibling providers' contract -- tavily's
`_response_objects` returns a format error for a non-object payload -- and
the same containment the search providers already apply.

Measured: 8 new parameterised cases fail on the base revision (5 for the
payload, 3 for the markdown field); 39 tests in the file, 122 across the
crawl4ai/browserless/sanitization neighbourhood, ruff check/format clean.
Each guard was mutation-checked separately.

backend/packages/harness/deerflow/community/crawl4ai/crawl4ai_client.py

@@ -44,10 +44,22 @@ class Crawl4AiClient:
                     content_type = resp.headers.get("content-type", "unknown")
                     return f"Error: Crawl4AI returned a non-JSON 200 response (content-type: {content_type}): {resp.text[:200]}"
 
+                # A JSON 200 that is not an object is a format error, not a
+                # success: indexing it raised "'list' object has no attribute
+                # 'get'" and the generic handler below echoed that Python text
+                # to the agent. Sibling providers (tavily's _response_objects)
+                # report a format error instead.
+                if not isinstance(data, dict):
+                    logger.error("Crawl4AI returned an unexpected payload type: %s", type(data).__name__)
+                    return "Error: Crawl4AI returned an unexpected response format"
+
                 if not data.get("success", False):
                     return f"Error: Crawl4AI reported failure for {url}"
 
                 markdown = data.get("markdown") or ""
+                if not isinstance(markdown, str):
+                    logger.error("Crawl4AI returned an unexpected 'markdown' payload type: %s", type(markdown).__name__)
+                    return "Error: Crawl4AI returned an unexpected response format"
                 if not markdown.strip():
                     return "Error: Crawl4AI returned empty markdown"
 

backend/tests/test_crawl4ai_tools.py

@@ -168,6 +168,67 @@ class TestCrawl4AiClient:
             assert result.startswith("Error: Crawl4AI returned a non-JSON 200 response")
             assert "text/html" in result
 
+    @pytest.mark.parametrize(
+        "payload",
+        [[{"markdown": "# ok"}], "maintenance window", 42, None, True],
+        ids=["payload-is-a-list", "payload-is-a-string", "payload-is-an-int", "payload-is-null", "payload-is-a-bool"],
+    )
+    async def test_fetch_markdown_non_object_200_reports_a_format_error(self, payload):
+        """A JSON 200 that is not an object is a format error, not a Python traceback.
+
+        Crawl4AI answers with a JSON object on success. A reverse proxy, a
+        version-skewed server or an error document delivered with HTTP 200 can
+        return a list or a bare scalar instead; indexing it directly raised
+        ``'list' object has no attribute 'get'`` and the generic handler echoed
+        that Python text to the agent. Sibling providers (tavily's
+        ``_response_objects``) report a format error instead.
+        """
+        with patch("deerflow.community.crawl4ai.crawl4ai_client.httpx.AsyncClient") as mock_cls:
+            mock_ctx = MagicMock()
+            mock_cls.return_value.__aenter__.return_value = mock_ctx
+
+            mock_resp = MagicMock()
+            mock_resp.status_code = 200
+            mock_resp.json.return_value = payload
+            mock_resp.headers = {"content-type": "application/json"}
+            mock_resp.text = json.dumps(payload)[:200]
+            mock_ctx.post = AsyncMock(return_value=mock_resp)
+
+            client = Crawl4AiClient(base_url="http://crawl4ai:11235")
+            result = await client.fetch_markdown("https://example.com")
+
+        assert result.startswith("Error: Crawl4AI returned an unexpected response format"), result
+        assert "object has no attribute" not in result
+
+    @pytest.mark.parametrize(
+        "markdown",
+        [["# heading"], 123, {"text": "# heading"}],
+        ids=["markdown-is-a-list", "markdown-is-an-int", "markdown-is-an-object"],
+    )
+    async def test_fetch_markdown_non_string_payload_reports_a_format_error(self, markdown):
+        """A non-string ``markdown`` field is the same format error, one level in.
+
+        ``data.get("markdown") or ""`` passes a list/dict/int straight through to
+        ``.strip()``, which raised ``'list' object has no attribute 'strip'`` --
+        the container guard above does not cover this field.
+        """
+        with patch("deerflow.community.crawl4ai.crawl4ai_client.httpx.AsyncClient") as mock_cls:
+            mock_ctx = MagicMock()
+            mock_cls.return_value.__aenter__.return_value = mock_ctx
+
+            mock_resp = MagicMock()
+            mock_resp.status_code = 200
+            mock_resp.json.return_value = {"success": True, "markdown": markdown}
+            mock_resp.headers = {"content-type": "application/json"}
+            mock_resp.text = "{}"
+            mock_ctx.post = AsyncMock(return_value=mock_resp)
+
+            client = Crawl4AiClient(base_url="http://crawl4ai:11235")
+            result = await client.fetch_markdown("https://example.com")
+
+        assert result.startswith("Error: Crawl4AI returned an unexpected response format"), result
+        assert "object has no attribute" not in result
+
 
 @pytest.mark.asyncio
 class TestCrawl4AiTools: