diff --git a/backend/packages/harness/deerflow/community/exa/tools.py b/backend/packages/harness/deerflow/community/exa/tools.py
index 974280402f..015d5f3f99 100644
--- a/backend/packages/harness/deerflow/community/exa/tools.py
+++ b/backend/packages/harness/deerflow/community/exa/tools.py
@@ -1,10 +1,38 @@
 import json
+import logging
 
 from exa_py import Exa
 from langchain.tools import tool
 
 from deerflow.config import get_app_config
 
+logger = logging.getLogger(__name__)
+
+DEFAULT_MAX_RESULTS = 5
+DEFAULT_CONTENTS_MAX_CHARACTERS = 1000
+
+
+def _coerce_positive_int(value: object, default: int, option: str) -> int:
+    """Normalize a config value before handing it to the Exa SDK.
+
+    ``$VAR`` references in config.yaml resolve to strings, and exa-py rejects a
+    string ``num_results`` outright, so every search would fail. Only an integer
+    or an integer-form string is accepted: ``int()`` would silently truncate a
+    float such as an unquoted ``3.5`` and turn ``true`` into 1. Anything else
+    (blank, non-numeric, fractional, boolean, zero or negative) warns and keeps
+    the default instead.
+    """
+    if isinstance(value, int) and not isinstance(value, bool):
+        count = value
+    elif isinstance(value, str) and value.strip().isdecimal():
+        count = int(value.strip())
+    else:
+        count = 0
+    if count <= 0:
+        logger.warning("Invalid Exa %s=%r; using default %s", option, value, default)
+        return default
+    return count
+
 
 def _get_exa_client(tool_name: str = "web_search") -> Exa:
     config = get_app_config().get_tool_config(tool_name)
@@ -23,13 +51,17 @@ def web_search_tool(query: str) -> str:
     """
     try:
         config = get_app_config().get_tool_config("web_search")
-        max_results = 5
+        max_results = DEFAULT_MAX_RESULTS
         search_type = "auto"
-        contents_max_characters = 1000
+        contents_max_characters = DEFAULT_CONTENTS_MAX_CHARACTERS
         if config is not None:
-            max_results = config.model_extra.get("max_results", max_results)
+            max_results = _coerce_positive_int(config.model_extra.get("max_results", max_results), DEFAULT_MAX_RESULTS, "max_results")
             search_type = config.model_extra.get("search_type", search_type)
-            contents_max_characters = config.model_extra.get("contents_max_characters", contents_max_characters)
+            contents_max_characters = _coerce_positive_int(
+                config.model_extra.get("contents_max_characters", contents_max_characters),
+                DEFAULT_CONTENTS_MAX_CHARACTERS,
+                "contents_max_characters",
+            )
 
         client = _get_exa_client()
         res = client.search(
diff --git a/backend/tests/test_exa_tools.py b/backend/tests/test_exa_tools.py
index b7196918ee..bd1778cbc5 100644
--- a/backend/tests/test_exa_tools.py
+++ b/backend/tests/test_exa_tools.py
@@ -133,6 +133,52 @@ class TestWebSearchTool:
 
         assert result == "Error: API rate limit exceeded"
 
+    def test_search_accepts_env_var_string_limits(self):
+        """``$VAR`` config references resolve to strings; exa-py rejects a string num_results."""
+        from exa_py import Exa
+
+        with patch("deerflow.community.exa.tools.get_app_config") as mock_config:
+            tool_config = MagicMock()
+            tool_config.model_extra = {"max_results": "10", "contents_max_characters": "2000", "api_key": "test-key"}
+            mock_config.return_value.get_tool_config.return_value = tool_config
+
+            sent = {}
+
+            def fake_request(self, endpoint, data=None, *args, **kwargs):
+                sent.update(data or {})
+                return {"results": [], "requestId": "req"}
+
+            # The real SDK does the type check, so only its HTTP layer is replaced.
+            with patch.object(Exa, "request", fake_request):
+                from deerflow.community.exa.tools import web_search_tool
+
+                result = web_search_tool.invoke({"query": "test query"})
+
+        assert json.loads(result) == []
+        assert sent["numResults"] == 10
+        assert sent["contents"] == {"highlights": {"maxCharacters": 2000}}
+
+    @pytest.mark.parametrize("raw", [None, "", "many", "3.5", 3.5, 10.0, True, False, 0, -2, "-2"])
+    def test_search_invalid_limits_fall_back_to_defaults(self, mock_exa_client, raw):
+        """An unusable value warns and keeps the default instead of failing the search."""
+        with patch("deerflow.community.exa.tools.get_app_config") as mock_config:
+            tool_config = MagicMock()
+            tool_config.model_extra = {"max_results": raw, "contents_max_characters": raw, "api_key": "test-key"}
+            mock_config.return_value.get_tool_config.return_value = tool_config
+            mock_exa_client.search.return_value = MagicMock(results=[])
+
+            from deerflow.community.exa.tools import web_search_tool
+
+            result = web_search_tool.invoke({"query": "test query"})
+
+        assert json.loads(result) == []
+        mock_exa_client.search.assert_called_once_with(
+            "test query",
+            type="auto",
+            num_results=5,
+            contents={"highlights": {"max_characters": 1000}},
+        )
+
 
 class TestWebFetchTool:
     def test_basic_fetch(self, mock_app_config, mock_exa_client):
diff --git a/backend/tests/test_feishu_parser.py b/backend/tests/test_feishu_parser.py
index 27bbca91d2..5acc1896f2 100644
--- a/backend/tests/test_feishu_parser.py
+++ b/backend/tests/test_feishu_parser.py
@@ -563,6 +563,8 @@ def _make_file_event(
 def test_feishu_batches_top_level_file_messages_from_same_user(monkeypatch):
     async def go():
         monkeypatch.setattr("app.channels.feishu.FEISHU_INBOUND_BATCH_WINDOW_SECONDS", 0.01)
+        # Keep both callbacks inside the batch window even on a busy CI runner.
+        monkeypatch.setattr("app.channels.feishu.time.time", lambda: 1_000.0)
         bus = MessageBus()
         channel = FeishuChannel(bus, {"app_id": "test", "app_secret": "test"})
         channel._main_loop = asyncio.get_running_loop()