fix(mcp): eliminate duplicate config loading during startup (#69)

* fix(mcp): eliminate duplicate config loading during startup

load_mcp_config() was called twice on every startup — once in
_mcp_config_signature() to compute the cache key, and again inside
load_mcp_tools(). This caused warnings to appear twice.

Merge the two calls into _load_mcp_config_once() which returns both the
signature and the parsed config, then pass the config through to
load_mcp_tools() via a new optional parameter.

* test(mcp): fix existing cache tests and add coverage for single-load guarantee

- Update fake_load_mcp_tools to accept optional config kwarg
- Add test_load_mcp_config_called_once_per_cache_miss: verifies
  load_mcp_config is called exactly once per cache miss (the bug)
- Add test_cached_config_passed_to_load_mcp_tools: verifies the
  pre-loaded config dict is forwarded to load_mcp_tools

---------

Co-authored-by: Xi Zhang <106144707+X-iZhang@users.noreply.github.com>

EvoScientist/EvoScientist.py

@@ -89,18 +89,18 @@ def _ensure_chat_model():
 # =============================================================================
 
 
-def _mcp_config_signature() -> str:
-    """Return a stable signature for the effective MCP config."""
+def _load_mcp_config_once() -> tuple[str, dict]:
+    """Load MCP config and return ``(signature, config)``."""
     from .mcp.client import load_mcp_config
 
     cfg = load_mcp_config()
     if not cfg:
-        return ""
+        return "", {}
     try:
-        return json.dumps(cfg, sort_keys=True, ensure_ascii=True)
+        sig = json.dumps(cfg, sort_keys=True, ensure_ascii=True)
     except TypeError:
-        # Fallback for non-JSON-serializable values (should be rare)
-        return repr(cfg)
+        sig = repr(cfg)
+    return sig, cfg
 
 
 def _load_mcp_tools_cached() -> dict[str, list]:
@@ -109,7 +109,7 @@ def _load_mcp_tools_cached() -> dict[str, list]:
 
     from .mcp import load_mcp_tools
 
-    cfg_key = _mcp_config_signature()
+    cfg_key, cfg = _load_mcp_config_once()
     if not cfg_key:
         _MCP_TOOLS_CACHE_KEY = ""
         _MCP_TOOLS_CACHE_VALUE = {}
@@ -118,7 +118,7 @@ def _load_mcp_tools_cached() -> dict[str, list]:
     if _MCP_TOOLS_CACHE_KEY == cfg_key and _MCP_TOOLS_CACHE_VALUE is not None:
         return {k: list(v) for k, v in _MCP_TOOLS_CACHE_VALUE.items()}
 
-    loaded = load_mcp_tools()
+    loaded = load_mcp_tools(config=cfg)
     _MCP_TOOLS_CACHE_KEY = cfg_key
     _MCP_TOOLS_CACHE_VALUE = {k: list(v) for k, v in loaded.items()}
     return {k: list(v) for k, v in loaded.items()}

EvoScientist/mcp/client.py

@@ -660,12 +660,17 @@ async def _load_tools(config: dict[str, Any]) -> dict[str, list]:
     return server_tools
 
 
-async def aload_mcp_tools() -> dict[str, list]:
+async def aload_mcp_tools(config: dict[str, Any] | None = None) -> dict[str, list]:
     """Async version of :func:`load_mcp_tools`.
 
     Prefer this when already inside an async context (e.g. Jupyter, async CLI).
+
+    Args:
+        config: Optional pre-loaded MCP config dict.  When ``None``,
+            loads from ``~/.config/evoscientist/mcp.yaml``.
     """
-    config = load_mcp_config()
+    if config is None:
+        config = load_mcp_config()
     if not config:
         return {}
     try:
@@ -676,7 +681,7 @@ async def aload_mcp_tools() -> dict[str, list]:
     return _route_tools(config, server_tools)
 
 
-def load_mcp_tools() -> dict[str, list]:
+def load_mcp_tools(config: dict[str, Any] | None = None) -> dict[str, list]:
     """Load MCP tools and return them grouped by target agent.
 
     This is the main synchronous entry point. It:
@@ -685,12 +690,19 @@ def load_mcp_tools() -> dict[str, list]:
     3. Filters tools per server allowlist
     4. Routes tools to target agents
 
+    Args:
+        config: Optional pre-loaded MCP config dict.  When ``None``,
+            loads from ``~/.config/evoscientist/mcp.yaml``.  Passing a
+            pre-loaded config avoids duplicate env-var interpolation
+            warnings when the caller has already loaded the config.
+
     Returns:
         Dict mapping agent name -> list of LangChain ``BaseTool`` objects.
         Key ``"main"`` = main agent. Other keys = subagent names.
         Returns empty dict if no MCP servers are configured.
     """
-    config = load_mcp_config()
+    if config is None:
+        config = load_mcp_config()
     if not config:
         return {}
 

tests/test_agent_mcp_cache.py

@@ -23,7 +23,7 @@ class TestMcpToolCaching:
             lambda: {"srv": {"transport": "stdio", "command": "demo"}},
         )
 
-        def fake_load_mcp_tools():
+        def fake_load_mcp_tools(config=None):
             calls["load"] += 1
             return {"main": [tool]}
 
@@ -44,7 +44,7 @@ class TestMcpToolCaching:
         def fake_load_config():
             return state["cfg"]
 
-        def fake_load_mcp_tools():
+        def fake_load_mcp_tools(config=None):
             calls["load"] += 1
             return {"main": [f"tool-v{calls['load']}"]}
 
@@ -57,3 +57,39 @@ class TestMcpToolCaching:
 
         assert calls["load"] == 2
         assert first != second
+
+    def test_load_mcp_config_called_once_per_cache_miss(self, monkeypatch):
+        """load_mcp_config should be called exactly once per cache miss,
+        not twice (once for the signature and once inside load_mcp_tools)."""
+        calls = {"config": 0}
+
+        def counting_load_config():
+            calls["config"] += 1
+            return {"srv": {"transport": "stdio", "command": "demo"}}
+
+        monkeypatch.setattr(
+            "EvoScientist.mcp.client.load_mcp_config", counting_load_config
+        )
+        monkeypatch.setattr(
+            "EvoScientist.mcp.load_mcp_tools", lambda config=None: {"main": []}
+        )
+
+        agent_module._load_mcp_tools_cached()
+        assert calls["config"] == 1
+
+    def test_cached_config_passed_to_load_mcp_tools(self, monkeypatch):
+        """load_mcp_tools should receive the pre-loaded config dict."""
+        received = {}
+
+        def fake_load_config():
+            return {"srv": {"transport": "stdio", "command": "demo"}}
+
+        def fake_load_mcp_tools(config=None):
+            received["config"] = config
+            return {"main": []}
+
+        monkeypatch.setattr("EvoScientist.mcp.client.load_mcp_config", fake_load_config)
+        monkeypatch.setattr("EvoScientist.mcp.load_mcp_tools", fake_load_mcp_tools)
+
+        agent_module._load_mcp_tools_cached()
+        assert received["config"] == {"srv": {"transport": "stdio", "command": "demo"}}