fix: improve error handling in GitHub Copilot provider

[CZH-THU]

📝 Description

This PR improves error handling in the GitHub Copilot provider by:

1. Fixing ignored error: The SendAndWait method's error return value was previously ignored using _. Now it's properly handled and wrapped in a descriptive error message.

2. Improving error message: Enhanced the error message for the unimplemented stdio mode to provide clearer guidance to users, suggesting they use grpc mode instead.

3. Adding documentation: Added a TODO comment with a reference link to help future contributors implement the stdio mode.

These changes improve code reliability and user experience by ensuring errors are properly propagated and users receive helpful guidance.

🗣️ Type of Change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 📖 Documentation update
• ⚡ Code refactoring (no functional changes, no api changes)

🤖 AI Code Generation

• 🤖 Fully AI-generated (100% AI, 0% Human)
• 🛠️ Mostly AI-generated (AI draft, Human verified/modified)
• 👨‍💻 Mostly Human-written (Human lead, AI assisted or none)

🔗 Related Issue

📚 Technical Context (Skip for Docs)

• Reference URL:
  • https://github.com/github/copilot-sdk/blob/main/docs/getting-started.md
• Reasoning:
  • The SendAndWait method returns an error that should be checked to ensure proper error propagation
  • Ignoring errors can lead to silent failures and make debugging difficult
  • Better error messages help users understand what went wrong and how to fix it

🧪 Test Environment

• Hardware: PC
• OS: Windows 10
• Model/Provider: GitHub Copilot (not tested with actual provider, code review only)
• Channels: N/A (provider-level change)

📸 Evidence (Optional)

Click to view Logs/Screenshots

Before:

resp, _ := session.SendAndWait(ctx, copilot.MessageOptions{
    Prompt: string(fullcontent),
})

After:

resp, err := session.SendAndWait(ctx, copilot.MessageOptions{
    Prompt: string(fullcontent),
})

if err != nil {
    return nil, fmt.Errorf("failed to send message to copilot: %w", err)
}

☑️ Checklist

• My code/docs follow the style of this project.
• I have performed a self-review of my own changes.
• I have updated the documentation accordingly (added TODO comment with reference).
• Code passes linting checks (verified with read_lints).
• Commit message follows Conventional Commits format.

[nikolasdehor]

Review: fix: improve error handling in GitHub Copilot provider

Clean, focused fix. All three changes are improvements.

Analysis

1. SendAndWait error handling -- The original resp, _ := session.SendAndWait(...) silently discarded errors. This is a real bug -- if the Copilot session fails (network timeout, auth issue, rate limit), the code would proceed with a nil resp and hit the "empty response" error instead of the actual failure reason. The fix properly propagates the error with context ("failed to send message to copilot: %w").

2. Improved stdio error message -- Adding "please use 'grpc' mode instead" is helpful user guidance. The TODO with reference link is good for future contributors.

3. Error wrapping -- Using %w for error wrapping is correct Go convention, allowing callers to use errors.Is/errors.As for error inspection.

Minor Notes

4. The resp == nil check after the new error check is still valuable as a defensive guard (SDK could theoretically return nil response without error).

5. No test changes, but this is a provider that is hard to unit test without mocking the Copilot SDK. The fix is mechanical and safe.

LGTM. Straightforward correctness improvement.