Reserve prompt rows during automatic less paging - #3999
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September 7, 2026 18:28
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Add --paging-reserve=N and PrettyPrinter::paging_reserve to reserve terminal rows for a multiline shell prompt during automatic paging. This implements the prompt-reservation use case in #1620; negative offsets remain outside this option's scope.
Use less's LESS_LINES support, available in stable releases from 632 onward, to reduce both its viewport and its one-screen threshold. Ordinary reservations follow less's resize handling; a reservation that already fills the terminal leaves one row. Set the variable only for the child pager, overriding inherited LESS_LINES. Preserve forced and disabled paging, support repeated options, and apply automatic exit to custom less arguments. Unsupported pagers and older less versions report an actionable error when a reservation would be used.
Keep OutputType::from_mode compatible and add a separate constructor accepting the reservation. Wire the setting through normal output and theme previews. Document the viewport tradeoff in help, README and the manual; update all four completions.
Validation: all 478 all-feature tests passed (7 ignored), including new checks for argument validation, repeated settings, child pager configuration, old/unrecognized versions and forced-paging behavior. All 8 default-feature help tests, all-target/all-feature Clippy with warnings denied, the minimal library build, formatting, whitespace checks and Bash/Zsh completion syntax passed. Twelve real PTY checks against less 668 verified the automatic threshold, short output, disabled/forced paging, visible ranges, wrapped rows, custom arguments, oversized reservations and unsupported pagers. The standalone PTY regression script is included.
Fixes #1620.