fix(filesystem): make move_file fail instead of silently overwriting the destination

src/filesystem/__tests__/lib.test.ts

@@ -14,6 +14,7 @@ import {
   getFileStats,
   readFileContent,
   writeFileContent,
+  moveFile,
   // Search & filtering functions
   searchFilesWithValidation,
   // File editing functions
@@ -310,6 +311,29 @@ describe('Lib Functions', () => {
       });
     });
 
+    describe('moveFile', () => {
+      it('moves the file when the destination does not exist', async () => {
+        const enoent = Object.assign(new Error('not found'), { code: 'ENOENT' });
+        mockFs.lstat.mockRejectedValueOnce(enoent);
+        mockFs.rename.mockResolvedValueOnce(undefined);
+
+        await moveFile('/test/source.txt', '/test/dest.txt');
+
+        expect(mockFs.rename).toHaveBeenCalledWith('/test/source.txt', '/test/dest.txt');
+      });
+
+      it('fails without overwriting when the destination already exists', async () => {
+        // lstat resolving means the destination is occupied.
+        mockFs.lstat.mockResolvedValueOnce({} as any);
+
+        await expect(moveFile('/test/source.txt', '/test/dest.txt')).rejects.toThrow(
+          'Destination already exists'
+        );
+
+        expect(mockFs.rename).not.toHaveBeenCalled();
+      });
+    });
+
   });
 
   describe('Search & Filtering Functions', () => {

src/filesystem/index.ts

@@ -21,6 +21,7 @@ import {
   getFileStats,
   readFileContent,
   writeFileContent,
+  moveFile,
   searchFilesWithValidation,
   applyFileEdits,
   tailFile,
@@ -631,7 +632,7 @@ server.registerTool(
   async (args: z.infer<typeof MoveFileArgsSchema>) => {
     const validSourcePath = await validatePath(args.source);
     const validDestPath = await validatePath(args.destination);
-    await fs.rename(validSourcePath, validDestPath);
+    await moveFile(validSourcePath, validDestPath);
     const text = `Successfully moved ${args.source} to ${args.destination}`;
     const contentBlock = { type: "text" as const, text };
     return {

src/filesystem/lib.ts

@@ -185,6 +185,25 @@ export async function writeFileContent(filePath: string, content: string): Promi
 }
 
 
+export async function moveFile(sourcePath: string, destinationPath: string): Promise<void> {
+  // The move_file tool contract (and README) state the operation fails if the
+  // destination already exists. fs.rename would silently overwrite it, which is
+  // a data-loss bug, so reject up front when anything - file, directory, or
+  // symlink - occupies the target. lstat is used so an existing symlink at the
+  // destination is detected rather than followed.
+  try {
+    await fs.lstat(destinationPath);
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
+      await fs.rename(sourcePath, destinationPath);
+      return;
+    }
+    throw error;
+  }
+  throw new Error(`Destination already exists: ${destinationPath}`);
+}
+
+
 // File Editing Functions
 interface FileEdit {
   oldText: string;