test(benchmark): standardize agent-loop performance matrix

tests/benchmark/adapters/openchrome-adapter.ts

@@ -10,10 +10,11 @@ export interface OpenChromeAdapterOptions {
  * Returns mock responses without connecting to a real MCP server.
  * Use for deterministic tool call count and regression testing.
  */
-export class OpenChromeStubAdapter implements MCPAdapter {
-  name = 'OpenChrome';
-  mode: string;
-  private options: OpenChromeAdapterOptions;
+export class OpenChromeStubAdapter implements MCPAdapter {
+  name = 'OpenChrome';
+  mode: string;
+  private options: OpenChromeAdapterOptions;
+  private tabSeq = 0;
 
   private _totalInputChars = 0;
   private _totalOutputChars = 0;
@@ -37,9 +38,12 @@ export class OpenChromeStubAdapter implements MCPAdapter {
     this._totalInputChars += inputJson.length;
 
     // Stub response - no actual MCP server connection
-    const result: MCPToolResult = {
-      content: [{ type: 'text', text: 'stub response' }],
-    };
+    const text = toolName === 'tabs_create'
+      ? JSON.stringify({ tabId: `stub-${this.mode}-tab-${++this.tabSeq}` })
+      : 'stub response';
+    const result: MCPToolResult = {
+      content: [{ type: 'text', text }],
+    };
 
     const outputJson = JSON.stringify(result);
     this._totalOutputChars += outputJson.length;
@@ -60,12 +64,13 @@ export class OpenChromeStubAdapter implements MCPAdapter {
     return this._toolCallCount;
   }
 
-  resetMetrics(): void {
-    this._totalInputChars = 0;
-    this._totalOutputChars = 0;
-    this._toolCallCount = 0;
-  }
-}
+  resetMetrics(): void {
+    this._totalInputChars = 0;
+    this._totalOutputChars = 0;
+    this._toolCallCount = 0;
+    this.tabSeq = 0;
+  }
+}
 
 /**
  * @deprecated Use OpenChromeStubAdapter instead.