refactor(core): centralize path validation and allow temp dir access for tools (#17185)

Co-authored-by: Your Name <joshualitt@google.com>

packages/core/src/tools/write-file.ts

@@ -5,6 +5,7 @@
  */
 
 import fs from 'node:fs';
+import fsPromises from 'node:fs/promises';
 import path from 'node:path';
 import * as Diff from 'diff';
 import { WRITE_FILE_TOOL_NAME } from './tool-names.js';
@@ -245,6 +246,18 @@ class WriteFileToolInvocation extends BaseToolInvocation<
   }
 
   async execute(abortSignal: AbortSignal): Promise<ToolResult> {
+    const validationError = this.config.validatePathAccess(this.resolvedPath);
+    if (validationError) {
+      return {
+        llmContent: validationError,
+        returnDisplay: 'Error: Path not in workspace.',
+        error: {
+          message: validationError,
+          type: ToolErrorType.PATH_NOT_IN_WORKSPACE,
+        },
+      };
+    }
+
     const { content, ai_proposed_content, modified_by_user } = this.params;
     const correctedContentResult = await getCorrectedFileContent(
       this.config,
@@ -282,8 +295,10 @@ class WriteFileToolInvocation extends BaseToolInvocation<
 
     try {
       const dirName = path.dirname(this.resolvedPath);
-      if (!fs.existsSync(dirName)) {
-        fs.mkdirSync(dirName, { recursive: true });
+      try {
+        await fsPromises.access(dirName);
+      } catch {
+        await fsPromises.mkdir(dirName, { recursive: true });
       }
 
       await this.config
@@ -453,12 +468,9 @@ export class WriteFileTool
 
     const resolvedPath = path.resolve(this.config.getTargetDir(), filePath);
 
-    const workspaceContext = this.config.getWorkspaceContext();
-    if (!workspaceContext.isPathWithinWorkspace(resolvedPath)) {
-      const directories = workspaceContext.getDirectories();
-      return `File path must be within one of the workspace directories: ${directories.join(
-        ', ',
-      )}`;
+    const validationError = this.config.validatePathAccess(resolvedPath);
+    if (validationError) {
+      return validationError;
     }
 
     try {