Greptile Summary

This PR extracts pierre theme loading into a new pierre-themes.ts module and fixes the extensions/diffs test failures caused by Node's stricter JSON module import requirements. Instead of using import … assert { type: "json" }, it reads the theme JSON files at runtime via fs.readFile and re-registers them in @pierre/diffs's internal RegisteredCustomThemes map, also clearing any stale entries in ResolvedThemes and ResolvingThemes before the next render.

• pierre-themes.ts (new): Singleton ensurePierreThemesRegistered() function that, on first call, registers lazy loaders for pierre-light and pierre-dark themes by finding @pierre/theme as a pnpm-layout sibling of @pierre/diffs and reading the JSON files with fs.readFile.
• render.ts: Adds await ensurePierreThemesRegistered() at the top of renderBeforeAfterDiff and renderPatchDiff, ensuring theme loaders are in place before preloadFileDiff / preloadMultiFileDiff run.
• Behavior change: The previous implementation (patchPierreThemeLoadersForNode24) wrapped path resolution in a try/catch and explicitly fell back to upstream loaders on any error. The new loadPierreTheme has no equivalent guard; a missing theme file will propagate as a render-time error rather than a silent fallback.

Confidence Score: 3/5

• PR is safe to merge in a pnpm environment but removes the silent-fallback safety net from the previous implementation.
• The core fix — using fs.readFile instead of JSON module imports — is sound and the pnpm path derivation mirrors what the old createRequire-based resolver produced. The one functional regression is the removal of the try/catch fallback that the previous code explicitly included to keep upstream loaders on path-resolution failures. Without it, any environment where @pierre/diffs isn't resolvable at the expected relative path will receive a render error instead of graceful degradation.
• extensions/diffs/src/pierre-themes.ts — the loadPierreTheme function lacks the error fallback that the previous implementation intentionally provided.

This is a comment left during a code review.
Path: extensions/diffs/src/pierre-themes.ts
Line: 9-16

Comment:
**Missing error fallback removed from old implementation**

The previous implementation wrapped path resolution and theme loader registration in a `try/catch` with an explicit fallback comment: `// Keep upstream loaders if theme files cannot be resolved.` That guard meant a broken theme install never caused a render failure — it gracefully degraded to the upstream loaders.

In the new code, `loadPierreTheme` calls `fs.realpath()` and `fs.readFile()` without any catch. If the resolved `@pierre/diffs` symlink doesn't exist at the expected relative location (e.g., in a flat `node_modules` or a different package manager), `fs.realpath` will throw `ENOENT`. Because `loadPierreTheme` is registered as a lazy callback in `RegisteredCustomThemes`, the error won't surface during `ensurePierreThemesRegistered()` — it will surface later as an uncaught rejection inside `preloadFileDiff` / `preloadMultiFileDiff`, causing every render to fail rather than falling back.

Consider wrapping the body of `loadPierreTheme` (or the entire registration callback) in a try/catch so that on resolution failure the slot is removed from `RegisteredCustomThemes` and `@pierre/diffs` retries with its own upstream loader:

```ts
async function loadPierreTheme(themeFileName: string, themeName: string): Promise<unknown> {
  try {
    const diffsPackageRoot = await fs.realpath(
      fileURLToPath(new URL("../node_modules/@pierre/diffs", import.meta.url)),
    );
    const themePath = path.join(diffsPackageRoot, "..", "theme", "themes", themeFileName);
    return {
      ...(JSON.parse(await fs.readFile(themePath, "utf8")) as Record<string, unknown>),
      name: themeName,
    };
  } catch {
    // Fall back to upstream loaders if theme files cannot be resolved.
    return undefined;
  }
}
```

How can I resolve this? If you propose a fix, please make it concise.

_{Last reviewed commit: 09e2e5f}

Merged via squash.

• Prepared head SHA: dd456aa32b85ce9b037141e0361e2c484efd8f0e
• Merge commit: 29674d75fb78ad8fc90e57a958268824cae68e5a

Thanks @NickHood1984!