* Vi mode P0 improvements: half-page scroll, visible cursor, gg fix
Three changes to keyboard copy mode (vi mode):
1. Ctrl+U/D now scroll half-page (was full-page). Ctrl+B/F remain
full-page. Uses Ghostty's scroll_page_fractional binding.
2. Entering copy mode now creates a 1-cell selection at the terminal
cursor via select_cursor_cell, giving the user a visible cursor
indicator. Visual mode (v) is tracked separately from Ghostty's
has_selection so the cursor selection doesn't make every motion
behave as visual. Exiting visual mode (v again) collapses back
to the cursor cell.
3. Single 'g' is now a prefix key requiring 'gg' to scroll to top,
matching standard vim behavior. Uses the same pendingG state
machine pattern as pendingYankLine for 'yy'.
Part of https://github.com/manaflow-ai/cmux/issues/846
* Fix viewport row refresh with persistent cursor selection
The 1-cell cursor selection made refreshKeyboardCopyModeViewportRowFromVisibleAnchor
always bail (has_selection was always true). Guard on keyboardCopyModeVisualActive
instead so viewport row updates work after scrolling in non-visual mode. Also
re-creates the cursor cell after refresh to preserve visibility.
Additionally: use performBindingAction(_:repeatCount:) for scrollHalfPage,
add state-reset assertion to testGGWithSelectionAdjustsToHome.
Addresses review feedback from CodeRabbit, Cubic, Codex, and Greptile.
044a3dbb64