feat(ui): Version History block/word-level diff (Compare) (PVH-6)

[eliotlim]

What & why

The last Version History slice (PVH-6): a Compare mode in the history side pane that shows a real block/word-level diff of a captured version against the current document — not just two read-only previews.

• Block alignment is an order-preserving LCS over top-level blocks keyed by stable block id: an aligned pair is unchanged/changed, an old-only block is removed, a new-only block is added.
• Changed text blocks get an intra-block word-level diff (kept/added/removed runs) rendered with semantic <ins>/<del> (never colour-only), tinted emerald / destructive / amber.
• Non-text blocks (image, chart, table, embed…) are reported opaquely as a "{Type} changed" badge rather than pretending to diff their internals.
• Long unchanged-context runs collapse behind a toggle. Pure engine (lib/blockDiff.ts, plain BlockJSON in / data out), unit-tested; no diff dependency added (the word-LCS is ~20 lines).

Before / After

Before = base main (the history pane's disabled Compare (coming soon) placeholder). After = this branch.

Behaviour	Before	After
Compare a version vs current: added + removed + inline word-level changed + an opaque non-text chip, together	read-only preview only; Compare disabled	quick→slow ins/del · removed row struck through · Image changed chip · added row
Dark mode — emerald / destructive / amber tint contrast
Preview | Compare toggle (light / dark)	text: single disabled "Compare (coming soon)" button
No-changes state (identical / empty-vs-empty version)		"No changes — this version matches the current document."

Review fixes applied (Quinn + Devon — batched)

1. Empty-doc false positive (Quinn). decodeSnapshot→ensureNotEmpty injects a lone empty paragraph with a fresh random id into each decoded-empty doc, so empty-vs-empty diffed as removed+added. The engine now drops a lone trailing bare default paragraph from each side before aligning → truly empty-vs-empty reads "No changes" (blockDiff.ts, stripTrailingBareParagraph).
2. Blank "changed" row for formatting-only changes (Quinn Q2 / Devon Rebrand to OpenBook #1). The "(empty)" fallback was gated on oldBlock (always truthy for changed), so a text block with identical text but changed props/children rendered a blank row with a lone ~. Now gated on the word runs actually containing an ins/del; all-kept runs render a "Formatting changed" hint (new i18n key) (VersionDiff.tsx).
3. Opaque chip over-promise (Devon Load workspace from filesystem #2). Downgraded the copy so nothing claims an "old→new" pair for opaque changes — a "{Type} changed" badge is the honest representation (module doc + VersionDiff comments/copy).
4. aria-label collision (Devon Navigation should update the currently open page #3). The toggle wrapper and the diff content root both used aria-label="Compare". The toggle wrapper now uses a dedicated "View mode" label; "Compare" is reserved for the button + diff content (HistoryPaneBody.tsx).
5. Dead copy/branches (Devon Novel has multiple unresolved vulnerabilities #4/Feature: use blocknote to replace novel #5). Removed the unused history.diffShowUnchanged key and the unreachable singular UnchangedRun branch + its singular diffUnchangedRun string (the run only renders for count ≥3 → plural only).
6. Tests (Quinn). Added locking tests: empty-doc-vs-empty → no change; trailing bare paragraph is not a change; and the MAX_WORD_TOKENS whole-block +/− fallback.

(Devon #6 — the "Computing changes…" flash on every Preview↔Compare toggle — left as-is: VersionDiff unmounts on toggle and refetches the live page, so a safe cache would risk staleness for marginal gain. Noted for follow-up.)

By-design (reviewer product-confirm flags)

• Nested-container edits (a change inside a table/columns/group) surface as a single opaque "{Type} changed" chip on the container, not a drill-down diff — intentional at this granularity.
• Word-diff granularity is unicode word/whitespace/punctuation tokens (grapheme-level, \p{L}\p{N}); it does not diff below the token.
• Reorders surface as remove+add (block moves are not tracked — owner listed move-tracking as optional).

Verify

build:libs · ui typecheck · ui build · ui lint · ui vitest all green (observed exit 0). Vitest: 1099 passed (incl. 14 in blockDiff.test.ts). Captures driven through the web e2e harness (seed a page whose captured version differs from current; Compare in light + dark).

Gates: design (Devon) + code (Quinn) — both CLEAR WITH NITS; all nits applied in the fix commit on this branch.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KFk2T9k3p7ghCjdzMfkA5w

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Project	Deployment	Actions	Updated (UTC)
app.book.pub	Ready	Preview, Comment	Jul 14, 2026 10:47am