Summary

Adds an optional filePath parameter to evaluate_script that saves the script output to a file instead of returning it inline.

Refs #153

Motivation

Issue #153 requested filePath support for take_snapshot and evaluate_script. take_snapshot was addressed in #463. PR #248 previously attempted this but was closed due to conflicts. This PR implements the same feature on the current codebase, completing the remaining piece.

Changes

• Add optional filePath parameter to the evaluate_script schema
• Add context.validatePath(filePath) call for path validation
• Pass {filePath, context} options to performEvaluation()
• In performEvaluation(): when filePath is provided, save output via context.saveFile() with .json extension; otherwise return inline as before
• Update docs/tool-reference.md via npm run docs:generate
• Add unit test for file output

Key design decisions

• Same pattern as existing tools: Follows the context.saveFile() pattern established by take_snapshot (feat: support saving snapshots to file #463), take_screenshot, get_network_request (feat: support filePath for network request and response bodies #795), and performance tools (feat: support filePath in performance tools #686).
• Minimal change surface: Only performEvaluation() gains an optional options parameter. No new interfaces or abstractions.
• Backwards compatible: filePath is optional. When omitted, behavior is identical to before.

Testing

Unit test added (tests/tools/script.test.ts):

• Call evaluate_script with filePath set to a temp file
• Assert response contains "Output saved to"
• Assert file content matches the JSON-serialized return value
• Clean up temp file in finally block

Manual testing performed:

• () => document.title with filePath: /tmp/test.json → file contains "Example Domain"
• () => document.title without filePath → inline ```json block returned (no regression)
• () => Array.from({length: 100}, ...) with filePath → 100-item array saved correctly
• filePath pointing to non-existent directory → directory auto-created, file saved
• Relative path (test.json) → resolved to CWD, absolute path shown in response
• Function that throws → error returned, no partial file created
• Existing file as filePath → file overwritten completely