Migrate the diff renderer to @pierre/diffs

docs/architecture.md

@@ -60,7 +60,7 @@ That keeps the viewer static-hosting friendly while removing the brittle parts o
 
 ## Bundle tradeoffs
 
-The largest remaining deferred cost is still the diff renderer stack, primarily `@git-diff-view/*` and its highlighting internals. Its vendor stylesheet is served from `public/vendor/diff-view-pure.css` with a precompressed `.css.br` variant and injected only when a rich diff mounts, so the empty shell and non-diff artifacts do not pay that CSS cost. The stack remains because it still provides the best review-style UX for multi-file git patches, split/unified modes, and syntax-aware rendering with less product code than a bespoke replacement.
+The largest remaining deferred cost is still the diff renderer stack, now `@pierre/diffs` with its Shiki grammars. There is no vendor stylesheet: styles ship inside the library's shadow roots, so the empty shell and non-diff artifacts pay no diff CSS or JS cost at all — the whole stack loads only when a diff artifact mounts, behind the existing `next/dynamic` boundary.
 
 The JSON and markdown paths are now substantially lighter because:
 
@@ -71,12 +71,13 @@ The JSON and markdown paths are now substantially lighter because:
 
 ## Diff choice
 
-`agent-render` uses `@git-diff-view/react` plus git-diff `DiffFile` instances instead of `@codemirror/merge`.
+`agent-render` uses `@pierre/diffs` (`PatchDiff` per parsed patch file, `MultiFileDiff` for before/after contents) instead of `@codemirror/merge`.
 
-- `@git-diff-view/*` matches the product goal better because it is already shaped like a GitHub-style review surface
-- split and unified views are built in
-- syntax highlighting and diff affordances are stronger out of the box for artifact viewing
-- individual file patches can be rendered as a sequence while preserving filenames and boundaries
+- `@pierre/diffs` matches the product goal better because it is already shaped like a review surface
+- split and unified views are built in (`diffStyle` option)
+- Shiki-based syntax highlighting is stronger out of the box for artifact viewing
+- individual file patches can be rendered as a sequence while preserving filenames and boundaries via the repo's own `parseGitPatchBundle`
+- before/after content diffs are computed by the library itself, which the previous stack could not do from raw contents
 - CodeMirror remains the better fit for full source artifacts and markdown code fences
 
 `@codemirror/merge` stays a reasonable future option if the project ever needs a more editor-centric comparison workflow, but it is not the best default for shareable review artifacts.

docs/dependency-notes.md

@@ -10,7 +10,7 @@
 - `rehype-sanitize` - MIT
 - `@codemirror/*` - MIT
 - `@replit/codemirror-indentation-markers` - MIT
-- `@git-diff-view/*` - MIT
+- `@pierre/diffs` - Apache-2.0
 - `papaparse` - MIT
 - `lz-string` - MIT
 - `fflate` - MIT
@@ -30,7 +30,7 @@
 - `next` pins its nested `postcss` dependency to `8.5.14` via `package.json` overrides so Tailwind CSS v4's `postcss ^8.5.6` peer range is satisfied in the Next.js toolchain.
 - CodeMirror handles source artifacts and markdown code fences because it is excellent at read-only code presentation; JSON, markdown raw, and CSV raw views use lighter native source blocks.
 - `@replit/codemirror-indentation-markers` replaces custom indent-guide logic with a maintained CM6 extension.
-- `@git-diff-view/*` fits review-style diffs better than a generic merge editor for the current viewer. Its pure CSS file is mirrored into `public/vendor/diff-view-pure.css` with a Brotli-compressed `public/vendor/diff-view-pure.css.br` copy by `npm run assets:compress`, and loaded only by the diff renderer; `tests/diff-style-asset.test.ts` keeps those assets in sync with the package copy.
+- `@pierre/diffs` (diffs.com) renders review-style diffs from patch strings (`PatchDiff`) or raw before/after contents (`MultiFileDiff`). It is Shiki-based, styles itself inside shadow DOM (no vendor stylesheet to mirror or serve), and is themed through `--diffs-*` CSS custom properties set on `.diff-renderer-frame`. It is imported only through the `src/lib/diff/pierre-react.ts` bridge so the deferred chunk stays stable across webpack graphs.
 - `papaparse` handles CSV parsing; CSV rendering uses a native read-only table to avoid a data-grid dependency for the shipped static viewer.
 - `fflate` provides portable deflate/inflate support across iOS Safari and Android Chromium without relying on browser-specific compression streams.
 - `brotli-wasm` provides the arx/arx2/arx3 Brotli compression layer, including streaming decompression used to cap expanded output before allocating oversized decoded payloads.

docs/testing.md

@@ -47,7 +47,7 @@ The suite is intentionally split by responsibility:
 - visual tests protect empty state, artifact views, theme presentation, and compact-content spacing
 - component tests protect selector/disclosure UI contracts
 - unit tests protect transport codecs, envelope validation, diff parsing, and language inference
-- `npm run assets:compress` regenerates minified/precompressed public assets, including the ARX dictionaries and mirrored diff-view stylesheet
+- `npm run assets:compress` regenerates minified/precompressed public assets (the ARX dictionaries)
 - `npm run bench:codecs` protects arx/arx2 compressed-byte ratios and arx3 visible-character wins against the committed `scripts/bench-baseline.json`; its corpus is fixed in `scripts/bench-codecs.mjs` so unrelated source, docs, or package metadata edits do not create false codec regressions
 - `npm run check:build-budgets` reads the generated `.next` manifests after `npm run build` and fails if the homepage shell or key deferred renderer chunks exceed their gzip budgets