v1.40.0

Now I have enough context. Let me write the release notes based on the actual changes:

What's New

• Textbox content editing — Click, type, and edit text inside VML and DrawingML textboxes. Selection, caret rendering, and text updates work across body, header/footer, and table cell contexts.
• Zoom modes and fit-width — Set zoom as manual or fit-width (auto-fit to container). ui.zoom exposes mode, value, calculated fit-zoom, bounds, and viewport metrics; PDF documents measure at their rendered scale.
• Viewport metrics and responsive layout events — viewport-change event fires on container resize with measurements (document width, available width, fit-zoom). Consume viewport metrics from getViewportMetrics() to implement responsive zoom without polling.
• Font family combobox — Typeahead-enabled font picker in toolbar with per-document font options and substitution evidence (metric-safe vs. visual-only); dropdown stays in viewport.
• Comments API expansion — ui.comments.setActive() highlights a comment without scrolling; pendingSelection on pending comment events gives consumers the captured selection to pass to comment creation APIs.
• Text range viewport targets — ui.viewport.getRect() now accepts Document API text targets (addresses and segments), resolving to painted DOM rects for custom overlay and floating-UI anchoring.
• Scroll container exposure — ui.viewport.getScrollContainer() returns the actual scrollable ancestor (or null for document/window scroll), letting overlay consumers attach scroll listeners to the right element.
• Sidebar geometry signals — ui.viewport.observe fires when the comments rail opens/closes, invalidating cached viewport geometry.
• TOC interactions — Hover highlighting and section-link navigation for table of contents.

Improvements

• Column balancing at continuous breaks — Multi-column sections now balance correctly at continuous section breaks, matching Word's layout. Explicit column widths (equal or unequal) and per-column spacing extract accurately.
• Tracked change granularity — Inline cell changes within a whole-table tracked change consolidate into one logical change in the review API (groupTrackedChanges), mirroring the comments containment rule.
• Line break handling in mutations — Generated newlines in text-mode mutations serialize as Word-native <w:br/> elements; read model treats lineBreak nodes as \n so search/query/rewrite stay consistent.
• Caret geometry for tabs and soft breaks — Tab carets anchor to line top; soft-break continuation carets position at line start with alignment-aware offset instead of the page right edge.
• Page break suppression — Style-driven pageBreakBefore directly after an explicit page break no longer renders a redundant blank page, matching Word's structural rule.
• Textbox table content rendering — Tables inside textboxes render with correct alignment and text flow.
• Plan-engine block identity repair — Runtime self-healing of duplicate block identities on compile, preventing stale cross-document references.
• Font substitution evidence — Font reports carry per-face evidence (metric-safe, visual-only, glyph exceptions) from the docfonts registry, giving consumers the fidelity detail behind each substitution.

Fixes

• Table cell selection collapse — Dragging a body selection into an empty table cell no longer collapses the selection; prosemirror-tables normalization guard keeps the extended range.
• Multiline selection rendering — Interior lines of multi-line selections now render the full width highlight instead of slivers; per-line rect computation handles absolutely-positioned .superdoc-line elements across browsers.
• Empty cell geometry — Empty table cell paragraphs (no runs) resolve to their PM start instead of null, preventing frozen selections during active drags.
• Image alpha export — Process alphaModFix for images on export, preserving transparency properties.
• Text selection in generated lineBreak contexts — Search and offset resolution now treat lineBreak nodes as \n, so a match spanning text+lineBreak+text coalesces to one contiguous range.
• Font toolbar updates — Document font toolbar rebuilds and layout re-renders on fonts-changed events; dropdown state persists through editor handoff.
• UV-deprecated legacy visual testing infrastructure — Removed /devtools/visual-testing; layout validation now runs in the standard test suite.