Plan

Replace Region::Bottom(n) with a base region plus an optional line limit; the base slices raw screen lines (prompt box, above box, after last rule), then the existing normalization (trim, drop empty lines, keep the last n) applies. Add ScreenState::Hold; Store::apply_screen_state treats it as a no-op. Port claude.toml into crates/signaltty-agent/screen/, flattening herdr's nested gates with alternations and order-insensitive (?s) pairs.

Test-first: region and hold unit tests, Store hold test, Claude fixtures. Record the regions and hold in ADR-0026 and docs/07. A Claude review agent reviews the diff; no Gemini.