fix: add polyfill for getDefaultHighWaterMark to support VS Code 1.85.x

[roomote]

Summary

This PR fixes issue #6240 where the Roo Code extension fails to load on VS Code 1.85.x due to a missing Node.js API.

Problem

VS Code 1.85.x bundles Node.js 16.14.2, which doesn't include the getDefaultHighWaterMark function that was introduced in Node.js 16.7.0. The execa dependency (v9.5.2+) uses this API, causing the extension to fail during activation with:

TypeError: (0 , rBn.getDefaultHighWaterMark) is not a function

Solution

Added a polyfill for getDefaultHighWaterMark at the very beginning of extension.ts before any imports. The polyfill:

• Only adds the function if it doesn't already exist
• Uses the default values from Node.js source (16 for object mode, 16KB for regular mode)
• Is fully tested with comprehensive unit tests

Testing

• Added unit tests to verify the polyfill behavior
• All existing tests pass
• Linting and type checks pass

Impact

This fix allows users on older VS Code versions (1.84.0 - 1.85.x) to continue using the Roo Code extension without upgrading VS Code.

Fixes #6240

---

Important

Adds a polyfill for getDefaultHighWaterMark in extension.ts to support VS Code 1.85.x, with tests in extension-polyfill.spec.ts.

• Behavior:
  • Adds polyfill for getDefaultHighWaterMark in extension.ts to support VS Code 1.85.x using Node.js 16.14.2.
  • Polyfill uses default values from Node.js source (16 for object mode, 16KB for regular mode).
• Testing:
  • Adds unit tests in extension-polyfill.spec.ts to verify polyfill behavior.
  • Tests ensure the function is added if missing and does not override existing implementations.
• Impact:
  • Fixes issue Roocode does not load #6240, allowing Roo Code extension to work on VS Code 1.84.0 - 1.85.x without requiring a VS Code upgrade.

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[daniel-lxs]

Closing for now while we scope the issue