fix(core): fix test failures related to root execution and optional subagent_type

- Skip pathReader and edit tool permission tests when running as root
- Fix agent.test.ts to correctly mock execute call with extraHistory
- Remove unused imports in forkSubagent.ts

Author: wenshao

packages/core/src/tools/agent.test.ts

@@ -398,6 +398,7 @@ describe('AgentTool', () => {
       expect(mockAgent.execute).toHaveBeenCalledWith(
         mockContextState,
         undefined, // signal parameter (undefined when not provided)
+        { extraHistory: undefined }, // extraHistory
       );
 
       const llmText = partToString(result.llmContent);

packages/core/src/tools/agent.ts

@@ -239,7 +239,13 @@ assistant: "I'm going to use the ${ToolNames.AGENT} tool to launch the greeting-
       return 'Parameter "prompt" must be a non-empty string.';
     }
 
-    if (params.subagent_type) {
+    if (params.subagent_type !== undefined) {
+      if (
+        typeof params.subagent_type !== 'string' ||
+        params.subagent_type.trim() === ''
+      ) {
+        return 'Parameter "subagent_type" must be a non-empty string.';
+      }
       // Validate that the subagent exists (case-insensitive)
       const lowerType = params.subagent_type.toLowerCase();
       const subagentExists = this.availableSubagents.some(
@@ -481,13 +487,31 @@ class AgentToolInvocation extends BaseToolInvocation<AgentParams, ToolResult> {
       let extraHistory: Array<import('@google/genai').Content> | undefined;
 
       if (!this.params.subagent_type) {
-        const { FORK_AGENT, buildForkedMessages } = await import(
+        const { FORK_AGENT, buildForkedMessages, isInForkChild } = await import(
           '../agents/runtime/forkSubagent.js'
         );
         subagentConfig = FORK_AGENT;
         const geminiClient = this.config.getGeminiClient();
         if (geminiClient) {
           const rawHistory = geminiClient.getHistory(true);
+
+          if (isInForkChild(rawHistory)) {
+            const errorDisplay = {
+              type: 'task_execution' as const,
+              subagentName: FORK_AGENT.name,
+              taskDescription: this.params.description,
+              taskPrompt: this.params.prompt,
+              status: 'failed' as const,
+              terminateReason: 'Recursive forking is not allowed',
+            };
+
+            return {
+              llmContent:
+                'Error: Cannot create a fork from within an existing fork child. Please execute tasks directly.',
+              returnDisplay: errorDisplay,
+            };
+          }
+
           if (rawHistory.length > 0) {
             const lastMessage = rawHistory[rawHistory.length - 1];
             if (lastMessage.role === 'model') {

packages/core/src/tools/edit.test.ts

@@ -784,20 +784,23 @@ describe('EditTool', () => {
       expect(() => tool.build(params)).toThrow();
     });
 
-    it('should return FILE_WRITE_FAILURE on write error', async () => {
-      fs.writeFileSync(filePath, 'content', 'utf8');
-      // Make file readonly to trigger a write error
-      fs.chmodSync(filePath, '444');
-
-      const params: EditToolParams = {
-        file_path: filePath,
-        old_string: 'content',
-        new_string: 'new content',
-      };
-      const invocation = tool.build(params);
-      const result = await invocation.execute(new AbortController().signal);
-      expect(result.error?.type).toBe(ToolErrorType.FILE_WRITE_FAILURE);
-    });
+    it.skipIf(process.getuid && process.getuid() === 0)(
+      'should return FILE_WRITE_FAILURE on write error',
+      async () => {
+        fs.writeFileSync(filePath, 'content', 'utf8');
+        // Make file readonly to trigger a write error
+        fs.chmodSync(filePath, '444');
+
+        const params: EditToolParams = {
+          file_path: filePath,
+          old_string: 'content',
+          new_string: 'new content',
+        };
+        const invocation = tool.build(params);
+        const result = await invocation.execute(new AbortController().signal);
+        expect(result.error?.type).toBe(ToolErrorType.FILE_WRITE_FAILURE);
+      },
+    );
   });
 
   describe('getDescription', () => {

packages/core/src/utils/pathReader.test.ts

@@ -368,8 +368,10 @@ describe('readPathFromWorkspace', () => {
     ).rejects.toThrow('Path not found in workspace: not-found.txt');
   });
 
-  // mock-fs permission simulation is unreliable on Windows.
-  it.skipIf(process.platform === 'win32')(
+  // mock-fs permission simulation is unreliable on Windows and when running as root.
+  it.skipIf(
+    process.platform === 'win32' || (process.getuid && process.getuid() === 0),
+  )(
     'should return an error string if reading a file with no permissions',
     async () => {
       mock({