Fix review control surfaces found on the NVCA charter

[JSv4]

Summary

GUI QA on the NVCA Model COI (50 pages) turned up several control-surface problems with tracked edits, labels and comments. The main one was the reported bug: after labelling a passage, selecting other text and clicking Label did nothing visible, or labelled the previously selected paragraph.

Root causes and fixes

Labels and selection

• An injected .annot-label counted as paragraph text. The canvas text no longer matched the native text, so every labelled paragraph became contenteditable=false. Labels are now treated as generated content, both in canvasDom and in the viewer's selection mapping.
• A selection inside a read-only block reached only onAnchorSelect. The workspace then preferred the stale editor selection (editor.selection ?? requestedAnchor), so Label applied to the wrong block. The viewer now reports text selections in read-only blocks even when a canvas editor is attached, and the workspace uses whichever selection is newest.
• Labels and comments ignored the text selection and always covered the whole paragraph. AnnotationsPanel and CommentsPanel now accept a span, preview their target ("Selected text / Selected block"), and accept a focusRequest.
• In the demo, the quick-action bar shows the quoted target, comes back for each new selection after being dismissed, and focuses the Label/Comment field.

Tracked changes

• Every pure insertion used to borrow a neighbouring character. Typing after "stock." recorded del "." + ins ". This…". Docxodus 12.6.2 accepts zero-width replaceMatch spans, so insertions are now zero-width, which yields one clean w:ins that inherits the neighbour's rPr. The borrowed write stays as a fallback if the engine refuses.
• Documents saved with w:trackRevisions reopened with tracking off. DocxSessionController.open now honours the setting unless the host passes trackedChanges explicitly.
• The workspace had no tracking indicator, the toggle was buried in the Edit sidebar, and revisions were authored "docxodus" while comments and labels used "Reviewer". There's now an always-visible tracking toggle and a single revisionAuthor.

Presentation

• Engine .annot-highlight padding (1px 2px on each run fragment) opened gaps ("General .", "“ Certificate ”"). The viewer shadow root now sets padding-inline: 0.
• annotationMode: 'above' labels covered the preceding line. The workspace now uses tooltip.
• The formatting toolbar disappeared on non-Edit panels. It now stays on every panel.

Comments

• Replies were listed at the bottom, detached from their thread. They're now threaded under the root.
• Comment cards had no context. CommentsPanel takes an optional describeComment callback; the workspace supplies the highlighted text and page order.
• "Show comment" right after reply/resolve reported "not available in the current page layout" because re-pagination was still running. The workspace now retries when pagination completes, and only non-block anchors skip select() (which raised "Choose a paragraph or heading to edit").

New public API

• useSelectionTarget hook and the SelectionTarget type
• span / focusRequest props on AnnotationsPanel and CommentsPanel
• describeComment prop on CommentsPanel and the CommentContext type

Test plan

• npm run check (lint, 92 unit tests, build, API audit)
• npm run test:browser: 74 passed, 2 skipped (opt-in NVCA stress and PDF)
• New unit tests: zero-width insertion diffs, w:trackRevisions detection
• New browser tests: tracked end-of-paragraph typing gives a single insertion; an annotated paragraph stays editable; workspace labels/comments the selected word, including inside an already-labelled paragraph, and quick actions return after dismissal
• Manual pass on the NVCA charter: tracked append/replace/delete (4 clean revisions authored "Reviewer"), span labels and comments, reply/resolve/show, save → reopen keeps tracking on, and the original document opens untracked

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