VSC: Diagnostics consumed from VS Code, not LSP shim

[Hmbown]

Summary

The extension feeds VS Code's actual diagnostics back to the agent, which is richer than re-running an LSP shim.

Acceptance criteria

• Tool result for edits includes VS Code diagnostics for changed files.

Files

extensions/vscode/src/diagnostics.ts

Size

S

Source

Source tag: VSC. Add exact upstream/opencode source links during implementation if they are not already known. Do not copy external code blindly; port the behavior into this repo's architecture.

Filed from 2026-05-02 v0.8.8 intake.