Why

Sometimes "Highlight and add a note" scrolled the reader up to the top of the article, and the empty note waited, focused, further down. A new note's editor appears at the top of the article, invisible, until the margin measures it on the next frame. In about half of the tries it took focus while it was still up there, and the browser could scroll to the caret.

What changes

• In the margin, a new note's editor takes focus only once it stands beside its highlight, one frame later than before. Editing an existing note, the floating editor, the phone sheet and Home are unchanged.
• An editor that already has focus keeps its caret if the margin lays out again while you type.
• The textarea fallback (editor chunk unavailable, e.g. offline) focuses itself the same way. Its native autoFocus acts only on mount, so it would have stayed unfocused.

Verification

• The extended e2e test "Highlight and add a note" adds five notes further down the article. For each one it checks where the editor stands when it takes focus and that the page did not scroll. Against the production build:
  • with origin/main's components it failed 3 of 3 runs ("editor at -996");
  • with the fix it passed 3 of 3.
• All of highlights.spec.ts, home-highlights.spec.ts and the notebook specs pass, and pnpm verify passes.
• Fallback: a scratch spec that blocks the editor chunk showed the textarea focused beside its highlight with the page still. Without the change, it never took focus. Not kept: it needs service workers blocked.
• Fresh-context review ran (task, tests, public repo). Fixed from it: the exact focus count failed under the dev server's StrictMode, which focuses twice; the fallback focus; more notes and a scroll check in the test. Dismissed: an editor whose highlight is never measured is never focused. That case is theoretical, it was invisible before too, and the next click closes it with nothing lost.
• Not verified: the browser's own scroll to the caret. Automated Chromium and WebKit never scrolled, even with the editor focused 2,000 px above the screen, so the test checks the cause: where the editor is when it takes focus.