refactor: use context.saveFile() for file writing

Updates take_snapshot and evaluate_script to use context.saveFile()
instead of direct writeFile() calls, following the pattern established
in PR #250.

Changes:
- Removed direct fs/promises imports
- Convert string data to Uint8Array using TextEncoder
- Use context.saveFile() for consistent file writing
- Update response messages to use returned filename

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: aberemia24

src/tools/script.ts

@@ -3,7 +3,6 @@
  * Copyright 2025 Google LLC
  * SPDX-License-Identifier: Apache-2.0
  */
-import {writeFile} from 'node:fs/promises';
 
 import type {JSHandle} from 'puppeteer-core';
 import z from 'zod';
@@ -69,9 +68,11 @@ Example with arguments: \`(el) => {
         );
 
         if (request.params.filePath) {
-          await writeFile(request.params.filePath, result);
+          const encoder = new TextEncoder();
+          const data = encoder.encode(result);
+          const file = await context.saveFile(data, request.params.filePath);
           response.appendResponseLine(
-            `Saved script result to ${request.params.filePath}.`,
+            `Saved script result to ${file.filename}.`,
           );
         } else {
           response.appendResponseLine('Script ran on page and returned:');

src/tools/snapshot.ts

@@ -4,8 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import {writeFile} from 'node:fs/promises';
-
 import {Locator} from 'puppeteer-core';
 import z from 'zod';
 
@@ -41,10 +39,10 @@ identifier (uid). Always use the latest snapshot. Prefer taking a snapshot over
     const formattedSnapshot = formatA11ySnapshot(snapshot.root);
 
     if (request.params.filePath) {
-      await writeFile(request.params.filePath, formattedSnapshot);
-      response.appendResponseLine(
-        `Saved snapshot to ${request.params.filePath}.`,
-      );
+      const encoder = new TextEncoder();
+      const data = encoder.encode(formattedSnapshot);
+      const file = await context.saveFile(data, request.params.filePath);
+      response.appendResponseLine(`Saved snapshot to ${file.filename}.`);
     } else {
       response.setIncludeSnapshot(true);
     }