## Summary
- keep cursor at end-of-line after Up/Down history recall
- allow continued history navigation when recalled text cursor is at
start or end boundary
- add regression tests and document the history cursor contract in
composer docs
## Testing
- just fmt
- cargo test -p codex-tui --lib
history_navigation_leaves_cursor_at_end_of_line
- cargo test -p codex-tui --lib
should_handle_navigation_when_cursor_is_at_line_boundaries
- cargo test -p codex-tui *(fails in existing integration test
`suite::no_panic_on_startup::malformed_rules_should_not_panic` because
`target/debug/codex` is not present in this environment)*
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