Contribute rewrite Phase 2: split-pane preview with mermaid

Add a rendered preview pane and split the Contribute-mode center
column. Discuss mode is now a single rendered preview (no more
read-only Tiptap mount); Contribute mode renders the CM6 raw editor
on the left and a live-updating preview on the right at 50/50, with
the existing chat + change-card panels untouched on the right.

The new MarkdownPreview component renders markdown via marked and
lazy-loads mermaid on the first encounter of a ```mermaid fence in
any rendered doc. Mermaid (~200 KB gzipped, plus dagre/graphlib
subchunks) stays out of the main bundle and is fetched only when a
diagram actually appears in the rendered content. The marked
renderer is scoped via a per-component Marked instance so the
mermaid-fence behavior does not leak to Editor.jsx / DiffView.

XSS hardening on mermaid: securityLevel: 'strict' is set explicitly
in mermaid.initialize. Verified end-to-end via a sandbox eval — a
hostile `<script>window.X=true</script>` payload inside a mermaid
fence is neutralized (no script tags in the rendered SVG, no global
side-effect, diagram still renders with the offending node label
empty).

The §8.12 selection tooltip is now sourced from window.getSelection()
inside the preview surface rather than Tiptap PM positions. The
SelectionTooltip's existing `{text, coords}` contract is unchanged;
coords come from the selection range's bounding rect. Anchor payloads
for flag threads now carry just the quote text — the PM-position
from/to fields that the Tiptap-era code attached are dropped (they
were never meaningful as durable anchors anyway; quote is what §8.12
and §8.13 specify).

Design decisions confirmed before coding (all defaults):
- PromptBar spans both panes at the bottom of the center column; it
  operates on the document, not on either pane individually.
- Start-Contributing is a hard cut — no transition animation. Phase
  6's chat-drawer collapse will redo the layout machinery anyway.
- Mermaid lazy-loads on first ```mermaid fence detected, not on
  Contribute-mode entry. Keeps the gzipped cost off any doc that has
  no diagrams.
- Below 1280px viewport, a narrow-viewport banner surfaces in
  Contribute mode. The drawer collapse that fixes this properly is
  Phase 6.

Mermaid integration is kept loose for the future authoring tool: the
placeholder DOM node carries the source as a data attribute, the
renderer takes (source) → SVG via mermaid.render, and per-block
memoization keys on source. A future authoring pane can intercept
the placeholder before SVG render without restructuring.

SPEC §8.3 updated to reflect the split-pane Contribute layout — the
smallest edit that captures the new shape.

Verification notes:
- Vite preview on :5180 — sandbox mount of MarkdownPreview confirms
  rendering, mermaid SVG output, securityLevel:'strict' XSS
  neutralization, and the window.getSelection → {text, coords}
  bridge end to end.
- Network log confirms mermaid + sub-chunks are absent from initial
  load and fetched only after first ```mermaid encounter.
- Backend was not running this session, so the manual-debounce
  save-now / accept / decline / live-preview-mirror pathways were
  not driven against a real branch; they remain verified by
  inspection. Phase 1's verification gap therefore carries forward.
- 125 backend integration tests still green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

This commit is contained in:

Ben Stull

2026-05-25 10:24:19 -07:00

parent 5dbcac8906

commit 7c3b8fc133

6 changed files with 1426 additions and 42 deletions

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