[baseballyama]

Summary

This fixes editor bugs found by adversarially testing the /editor canvas. Several of them lost text, or made the screen differ from the saved document. Others acted on the wrong place: the previous caret, the paragraph above a table, or the whole run instead of a word.

Motivation

The maintainer reported that editing "still behaves strangely" and asked for thorough adversarial testing. Every finding below was reproduced in Chromium with a harness. After each action, the harness checks three things:

• each rendered paragraph and table cell against the model;
• that the serialized package is valid;
• the DOM caret against the model caret.

There is no linked issue.

Changes

Lost or diverging text (canvas)

• A key pressed right after a click acted on the previous caret, because selectionchange had not fired yet. For example, Enter + typing landed at the top of the document. The selection is now synced on every keydown and beforeinput.

• Typing into a paragraph with no runs was rendered but never reached the model. This covers Word's empty <w:p/> and the cells of a row added with Tab. Typing and IME there now go through insertTextCommand.

• These inputs used to let the browser restructure the DOM, and the model silently diverged from the screen:

  • ⌥⌫ / ⌘⌫ (word or line delete across runs);
  • Enter while an IME is composing;
  • a delete that empties a run;
  • insertParagraph from virtual keyboards;
  • spelling suggestions;
  • text drops;
  • Undo from the browser menu.

  beforeinput now leaves only plain typing, composition and one-character deletes inside a run to the browser. Everything else maps to the matching command, using getTargetRanges().

• ⌘A selected the page box, so typing over it wrecked the pages. ⌘A now selects the story: the body, or the open header or footer.

• ⌘↑ / ⌘↓ / ⌘Home / ⌘End left the caret between paragraphs. They now jump paragraph by paragraph and to the document start and end, as in Word.

• A click in the header or footer margin left the caret where it was. It now moves to the nearest body line.

Model commands (@office-kit/docx-editor)

• deleteSelectionCommand across table cells threw "not supported", and the canvas ignored the throw. Now:
  • within one table, the covered cells are emptied;
  • a selection that leaves the table deletes the rows it touches, and the text outside up to the table.
• mergeBackCommand after a table joined the paragraph to the one above the table. Now a paragraph with text stays put. An empty one is removed, unless it is the body's last paragraph, and the caret moves to the end of the last cell.
• Character formatting with a caret formatted the whole run. It now works as in Word:
  • inside a word, it formats the word (Intl.Segmenter, so Japanese works);
  • elsewhere, an empty run at the caret carries the formatting for the next typed text.
• runPoint steps over the zero-width placeholder of an empty run, so typing there stays in that run.
• New export: isEmptyParagraph.

Word behaviour (canvas)

• Enter in an empty list item moves it up a level, and at the top level ends the list.
• Backspace at the start of a list item removes its number.
• Backspace and Delete at paragraph edges never fall through to the browser.

Testing

• New unit tests:
  • range-edit.test.ts: cross-cell delete, delete from a paragraph into a table and from a table out of it, Backspace after a table (3 cases).
  • text-selection.test.ts: caret formatting for a word, a Japanese word, text typed next, and a double toggle.
• commands.test.ts: two bold tests used to pass only because a caret bolded the whole run. They now select the text they mean.
• pnpm test: 1278 passed, 8 skipped. pnpm typecheck, pnpm -r run typecheck, svelte-check, check:api-page and check:tree-shake all pass. oxlint reports the 2 known warnings.
• Chromium, /editor, en and ja: every scenario above was reproduced before the fix and passes after it. That includes CDP IME composition, Track Changes on, vertical text, a document with a bare <w:p/>, and a 40-paragraph two-page document.
• Random key fuzzing: 5 seeds, 200–250 steps each, plus 2 seeds with Track Changes on. The steps mix typing, Enter, Backspace/Delete, word delete, arrows, Shift selection, undo/redo, Bold, Tab, ⌘ jumps, ⌘A, IME and clicks. No DOM/model mismatch and no invalid package.

Breaking changes

None. Character formatting at a caret behaves differently, as described above, to match Word.

Checklist

• I have read CLAUDE.md and followed the project's conventions.
• I have added or updated tests for the change.
• I have added or updated documentation where user-visible behavior changed.
• If this is a breaking change, I have added a changeset / CHANGELOG entry and flagged it above.
• I have re-read my own diff and removed dead code, debug prints, and stale comments.
• If I used an LLM to draft this PR, I have verified each change myself, the PR represents real work that warrants a maintainer's review, and I am willing to defend each line in review.

🤖 Generated with Claude Code

https://claude.ai/code/session_01UAiVj14HzKtRDqK12BXTr6

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