fix(#3934): use MCP ImageContent for screenshots instead of embedding base64 in JSON

[laithrw]

Summary by cubic

Screenshots are now returned as MCP ImageContent instead of base64 in JSON. This reduces payload size and aligns outputs with MCP content types for browser_get_state and browser_screenshot.

• Refactors

  • Updated handle_call_tool to return mixed content lists (TextContent + ImageContent) when tools produce images.
  • Changed _get_browser_state and _screenshot to return (metadata_json, screenshot_b64 | None); dimensions remain in metadata.
  • Removed embedded "screenshot" from JSON; kept "size_bytes" and "viewport".
  • Updated browser_screenshot tool description to reflect the new format.
  • Lint cleanup and synced with main; no functional changes.

• Migration

  • Update clients to handle ImageContent in tool responses; parse TextContent for metadata and use ImageContent for the image.
  • Do not read "screenshot" from JSON; use "screenshot_dimensions" (browser_get_state) or "viewport" (browser_screenshot) for coordinates.
  • Expect handle_call_tool to return a list of content items for image-producing tools.

^{Written for commit a1e54ef. Summary will update on new commits.}

[github-actions]

Agent Task Evaluation Results: 2/2 (100%)

View detailed results

Task	Result	Reason
amazon_laptop	✅ Pass	Skipped - API key not available (fork PR or missing secret)
browser_use_pip	✅ Pass	Skipped - API key not available (fork PR or missing secret)

Check the evaluate-tasks job for detailed task execution logs.

[cubic-dev-ai]

No issues found across 1 file