- The model seat decides before consuming: a focused control that is not a row
(a retry button) keeps the browser's traversal, and Tab enters the list only
from the trigger.
- A launcher-opened menu is a fresh intent, so the dismissal that closed the
same token earlier no longer silences it.
- Comments and JSDoc now match the implementation: the near-end entry resumes
from the walk's last index, Shift+Tab leaves whenever the menu is open, and
the anchor hand-back names the control that opened the menu.
- The e2e focus assertions all go through `expect.poll`.
- Regression coverage for a rowless pane (the trigger keeps the keyboard) and
for a focused retry keeping its Tab, in the seat and the popup shell.
- The PR records the two public-surface changes (`SessionInput.focus()` in,
`bindComposerFocus` out) and the row-fill focus decision.
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