feat: support workspace variable interpolation in Provider Custom Headers

[roomote]

Summary

This PR attempts to address Issue #11165 by adding support for VS Code variable interpolation in Provider Custom Headers.

Changes

New Features

• Added interpolateHeaders function to src/utils/config.ts that supports:
  • ${workspaceFolder} - Full path to the workspace root
  • ${workspaceFolderBasename} - Just the folder name (e.g., my-repo-name)
  • ${env:VAR_NAME} - Environment variables

Integration Points

• Integrated header interpolation in buildApiHandler (src/api/index.ts) so all providers benefit automatically
• Updated getOpenAiModels function to interpolate headers when fetching models

Tests

• Added comprehensive tests for the interpolateHeaders function covering:
  • Basic variable interpolation
  • Environment variable interpolation
  • Mixed variables in headers
  • Edge cases (undefined, empty, missing variables)

Usage Example

After this change, users can configure a custom header like:

X-App-ID: ${workspaceFolderBasename}

And when working in a project at /home/user/projects/my-awesome-app, the actual header sent would be:

X-App-ID: my-awesome-app

Related Issues

Closes #11165

Feedback

Feedback and guidance are welcome!

---

Important

Add support for VS Code variable interpolation in provider custom headers via interpolateHeaders function.

• New Features:
  • Added interpolateHeaders function in config.ts to support ${workspaceFolder}, ${workspaceFolderBasename}, and ${env:VAR_NAME} in headers.
• Integration:
  • Integrated interpolateHeaders in buildApiHandler in index.ts and getOpenAiModels in openai.ts for automatic header interpolation.
• Tests:
  • Added tests for interpolateHeaders in config.spec.ts covering variable interpolation, environment variables, mixed variables, and edge cases.

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[roomote]

Rooviewer   See task on Roo Cloud

Review complete. No issues found.

The implementation correctly adds support for VS Code variable interpolation in Provider Custom Headers. The interpolateHeaders function properly handles ${workspaceFolder}, ${workspaceFolderBasename}, and ${env:VAR_NAME} patterns. All 28 tests pass.

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