VS Code extension: chat diff blocks hardcode Monaco theme "vs-dark", ignoring light themes

Summary

Chat diff blocks in the VS Code extension are always dark, ignoring both the VS Code color theme and the Claude Code theme setting. On a light VS Code theme the entire chat UI is light while every tool-call diff renders on a black background.

Environment

• Extension: anthropic.claude-code 2.1.246 (win32-x64)
• VS Code on Windows 11 Pro 26100
• VS Code color theme: light
• Claude Code theme: tried light via both /config theme=light and "theme": "light" in ~/.claude/settings.json — no effect

Cause

In webview/index.js, the two Monaco diff editors used for tool-call diffs are constructed with a hardcoded theme:

monaco.createDiffEditor(ref.current, {
  readOnly: true, renderSideBySide: true, renderOverviewRuler: false,
  scrollBeyondLastLine: false, minimap: { enabled: false }, automaticLayout: true,
  theme: "vs-dark",            // <-- hardcoded
  fontSize: 12, lineNumbers: "off", wordWrap: "on", ...
})

Both call sites pass the literal "vs-dark"; there are zero occurrences of theme:"vs" in the bundle. Nothing in contributes.configuration or in the settings schema (claude-code-settings.schema.json, which does define theme) reaches these editors.

Expected

The Monaco theme should follow the resolved Claude Code theme setting, or at minimum the host window's ColorThemeKind:

• light / light-* → "vs"
• dark / dark-* → "vs-dark"
• high contrast → "hc-light" / "hc-black"

theme: "auto" should track the VS Code theme live.

Repro

1. Set VS Code to any light color theme.
2. Run /config theme=light in the Claude Code panel.
3. Have Claude edit any file.
4. The diff block in the chat renders on a black background.

Workaround

Replacing both theme:"vs-dark" literals with theme:"vs" in the installed webview/index.js fixes it after a window reload, but is wiped on every extension update.