add fallback code

Signed-off-by: Anxhela Coba <acoba@redhat.com>

Author: Anxhela21

config/system.yaml

@@ -54,7 +54,7 @@ api:
       filesystem-tools:
         env_var: API_KEY              # Environment variable containing the token/key
 
-  # Legacy authentication (fallback when mcp_headers.enabled is false)
+  # Legacy authentication (fallback when mcp_headers is not configured or disabled)
   # Authentication via API_KEY environment variable only for MCP server
 
   # Retry configuration for 429 Too Many Requests API errors

src/lightspeed_evaluation/core/api/client.py

@@ -139,10 +139,16 @@ def _build_mcp_headers(self) -> dict[str, dict[str, str]]:
                 mcp_headers[server_name] = {header_name: header_value}
 
             if not mcp_headers:
-                raise APIError(
-                    "MCP headers are enabled, but no valid server credentials were resolved. "
-                    "Check mcp_headers.servers and required environment variables."
-                )
+                # Fallback to API_KEY if MCP headers are enabled but no credentials found
+                api_key = os.getenv("API_KEY")
+                if not api_key:
+                    raise APIError(
+                        "MCP headers are enabled, but no valid server credentials were resolved "
+                        "and no API_KEY environment variable is set. Check mcp_headers.servers "
+                        "and required environment variables, or set API_KEY as fallback."
+                    )
+                # Return empty dict to signal fallback to API_KEY authentication
+                return {}
             return mcp_headers
 
         # No MCP headers configured