fix: use platform path separator in attachment validation (#149)

isValidAttachmentPath() used hardcoded '/' separator which fails on
Windows where paths use '\'. Replace with node:path sep to support
both platforms. Also fix test to use join() instead of hardcoded '/'.

Co-authored-by: Dmitry Butko <dmitrybutko@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

src/lib/server/ws/attachment-validation.test.ts

@@ -43,7 +43,7 @@ describe('isValidAttachmentPath', () => {
 
 	it('rejects paths that match the prefix as a substring but are not inside it', () => {
 		// e.g. /tmp/copilot-uploads-evil/file.txt should not match /tmp/copilot-uploads/
-		expect(isValidAttachmentPath(UPLOAD_PREFIX + '-evil/file.txt')).toBe(false);
+		expect(isValidAttachmentPath(join(UPLOAD_PREFIX + '-evil', 'file.txt'))).toBe(false);
 	});
 });
 

src/lib/server/ws/attachments.ts

@@ -1,4 +1,4 @@
-import { resolve } from 'node:path';
+import { resolve, sep } from 'node:path';
 import { logSecurity } from '../security-log.js';
 import { UPLOAD_DIR_PREFIX } from './constants.js';
 
@@ -12,7 +12,7 @@ export type SdkAttachment =
 /** Validate that an attachment path is an absolute path inside the upload directory (prevents arbitrary file reads). */
 export function isValidAttachmentPath(filePath: string): boolean {
   const resolved = resolve(filePath);
-  return resolved.startsWith(UPLOAD_DIR_PREFIX + '/');
+  return resolved.startsWith(UPLOAD_DIR_PREFIX + sep);
 }
 
 /** Map client-sent attachments to the SDK format, validating paths and filtering invalid entries. */