feat: allow readFile tool to read images for vision-capable models

[zhanba]

Screenshot

Summary

• Extends the readFile tool to support reading image files for vision-capable AI models
• Adds MIME type detection and validation for media files
• Returns images as base64-encoded data with proper media type information
• Updates sanitize-message to handle media content types correctly
• Adds comprehensive test coverage for type safety with union return types

Implementation Details

• Added isSupportedMediaFile utility function to validate file types based on MIME types
• Modified readFile to return a union type supporting both text and media content
• Updated message sanitization logic to properly handle media types instead of just image types
• Added type guards in tests to ensure type safety when checking content

Related Issue

Fixes #539

Test Plan

• Unit tests pass for readFile with text files
• Unit tests pass for readFile with image files
• Type checking works correctly with union return types
• Pre-push hook tests pass successfully

🤖 Generated with Pochi

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (e220fd6) to head (063433f).
⚠️ Report is 720 commits behind head on main.

Additional details and impacted files

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##   main   #569   +/-   ##
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[Copilot]

Pull Request Overview

This PR adds support for reading and processing image files in the readFile tool for vision-capable AI models. The changes enable models with vision capabilities (like Google models) to receive images as base64-encoded data with proper MIME type information, extending the tool beyond text-only file reading.

Key Changes:

• Modified readFile tool to return a union type supporting both text and media content
• Added MIME type detection and validation utilities for media files
• Threaded supportedMimeTypes through the entire tool execution pipeline
• Updated message sanitization to handle media content appropriately

Reviewed Changes

Copilot reviewed 26 out of 27 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/vscode/src/tools/read-file.ts	Added media file reading logic with MIME type validation
packages/vscode/src/tools/test/read-file.test.ts	Added type guards for union return type handling in tests
packages/tools/src/read-file.ts	Converted to factory function with union output schema
packages/tools/src/index.ts	Introduced CreateToolOptions interface and threaded supportedMimeTypes
packages/common/src/tool-utils/media.ts	New utility for reading and validating media files
packages/common/src/tool-utils/fs.ts	Exported isPlainText function and added type field to ProcessedContent
packages/livekit-cf/src/lib/sanitize-message.ts	Updated to redact media data instead of just text content
packages/vendor-pochi/src/vendor.ts	Added supportedMimeTypes for Google models
Multiple integration files	Plumbed supportedMimeTypes through execution contexts

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