Use simple name for MCP tools where possible. (#4459)

packages/core/src/tools/mcp-tool.ts

@@ -28,15 +28,15 @@ export class DiscoveredMCPTool extends BaseTool<ToolParams, ToolResult> {
   constructor(
     private readonly mcpTool: CallableTool,
     readonly serverName: string,
-    readonly name: string,
-    readonly description: string,
-    readonly parameterSchemaJson: unknown,
     readonly serverToolName: string,
+    description: string,
+    readonly parameterSchemaJson: unknown,
     readonly timeout?: number,
     readonly trust?: boolean,
+    nameOverride?: string,
   ) {
     super(
-      name,
+      nameOverride ?? generateValidName(serverToolName),
       `${serverToolName} (${serverName} MCP Server)`,
       description,
       Icon.Hammer,
@@ -46,6 +46,19 @@ export class DiscoveredMCPTool extends BaseTool<ToolParams, ToolResult> {
     );
   }
 
+  asFullyQualifiedTool(): DiscoveredMCPTool {
+    return new DiscoveredMCPTool(
+      this.mcpTool,
+      this.serverName,
+      this.serverToolName,
+      this.description,
+      this.parameterSchemaJson,
+      this.timeout,
+      this.trust,
+      `${this.serverName}__${this.serverToolName}`,
+    );
+  }
+
   /**
    * Overrides the base schema to use parametersJsonSchema when building
    * FunctionDeclaration
@@ -166,3 +179,17 @@ function getStringifiedResultForDisplay(result: Part[]) {
 
   return '```json\n' + JSON.stringify(processedResults, null, 2) + '\n```';
 }
+
+/** Visible for testing */
+export function generateValidName(name: string) {
+  // Replace invalid characters (based on 400 error message from Gemini API) with underscores
+  let validToolname = name.replace(/[^a-zA-Z0-9_.-]/g, '_');
+
+  // If longer than 63 characters, replace middle with '___'
+  // (Gemini API says max length 64, but actual limit seems to be 63)
+  if (validToolname.length > 63) {
+    validToolname =
+      validToolname.slice(0, 28) + '___' + validToolname.slice(-32);
+  }
+  return validToolname;
+}