**Problem:**
GitHub Copilot API returns 400 error "missing required Copilot-Vision-Request
header for vision requests" when requests contain image content blocks, even
though the requests are valid Claude API calls.
**Root Cause:**
The GitHub Copilot executor was not detecting vision content in requests and
did not add the required `Copilot-Vision-Request: true` header.
**Solution:**
- Added `detectVisionContent()` function to check for image_url/image content blocks
- Automatically add `Copilot-Vision-Request: true` header when vision content is detected
- Applied fix to both `Execute()` and `ExecuteStream()` methods
**Testing:**
- Tested with Claude Code IDE requests containing code context screenshots
- Vision requests now succeed instead of failing with 400 errors
- Non-vision requests remain unchanged
Fixes issue where GitHub Copilot executor fails all vision-enabled requests,
causing unnecessary fallback to other providers and 0% utilization.
Co-Authored-By: Claude (claude-sonnet-4.5) <noreply@anthropic.com>
Enhance model definitions by including supported API endpoints for each model. This allows for better integration and usage tracking with the GitHub Copilot API.
Updated `applyPayloadConfig` to `applyPayloadConfigWithRoot` across payload translation logic, enabling validation against the original request payload when available. Added support for improved model normalization and translation consistency.
Add complete GitHub Copilot support including:
- Device flow OAuth authentication via GitHub's official client ID
- Token management with automatic caching (25 min TTL)
- OpenAI-compatible API executor for api.githubcopilot.com
- 16 model definitions (GPT-5 variants, Claude variants, Gemini, Grok, Raptor)
- CLI login command via -github-copilot-login flag
- SDK authenticator and refresh registry integration
Enables users to authenticate with their GitHub Copilot subscription and
use it as a backend provider alongside existing providers.
