fix: skip arg whitelist for handlers accepting **kwargs (#572) (#684)

* fix: skip arg whitelist for handlers accepting **kwargs (#572)

The schema-based argument filter (from #647) strips all kwargs not
declared in input_schema. This breaks handlers that accept **kwargs
for pass-through to ChromaDB or other backends.

Add inspect.Parameter.VAR_KEYWORD check before filtering — handlers
with **kwargs receive all arguments unfiltered.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: guard inspect.signature failure, default to filtering

Wrap inspect.signature() in try/except — on failure, default to
filtering (safe fallback). Addresses Copilot feedback on fragility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

mempalace/mcp_server.py

@@ -1350,8 +1350,21 @@ def handle_request(request):
             }
         # Whitelist arguments to declared schema properties only.
         # Prevents callers from spoofing internal params like added_by/source_file.
+        # Skip filtering if handler explicitly accepts **kwargs (pass-through).
+        # Default to filtering on inspect failure (safe fallback).
+        import inspect
+
         schema_props = TOOLS[tool_name]["input_schema"].get("properties", {})
-        tool_args = {k: v for k, v in tool_args.items() if k in schema_props}
+        try:
+            handler = TOOLS[tool_name]["handler"]
+            sig = inspect.signature(handler)
+            accepts_var_keyword = any(
+                p.kind == inspect.Parameter.VAR_KEYWORD for p in sig.parameters.values()
+            )
+        except (ValueError, TypeError):
+            accepts_var_keyword = False
+        if not accepts_var_keyword:
+            tool_args = {k: v for k, v in tool_args.items() if k in schema_props}
         # Coerce argument types based on input_schema.
         # MCP JSON transport may deliver integers as floats or strings;
         # ChromaDB and Python slicing require native int.