sl0p: collapse to a swap layout when the terminal gets narrow

Splitting a window into thirds is great until the window is 70 columns wide
and each pane gets 23. `responsive_min_cols` collapses the tab into the swap
layout named by `responsive_layout` when it gets narrower than that, and
restores the previously active layout when it grows back.

Selects a swap layout BY NAME rather than adding a size-aware
LayoutConstraint: that type crosses both the plugin protobuf API and the
client/server contract, and the committed prost assets cannot be regenerated
here (no protoc).

Restoring uses a 10-column hysteresis band. Without a dead band, dragging a
window edge that lands exactly on the threshold flips the layout on every
motion event, and every flip resizes every PTY in the tab.

"Did the user rearrange panes by hand" is judged from the damaged flag as
sampled BEFORE each resize, not the live one: resize_whole_tab's own
auto-layout pass sets that flag itself and clears it again only if it found a
layout that fits, so on a terminal too narrow for any of them it latches true
although nothing was rearranged. And once collapsed, restore stays reachable
regardless of the flag, so damage occurring while collapsed cannot strand the
tab in the narrow layout.

1 files changed, 10 insertions, 0 deletions

diff --git a/zellij-utils/src/kdl/mod.rs b/zellij-utils/src/kdl/mod.rs
index 8d7f4d9d..d7ea2de7 100644
--- a/zellij-utils/src/kdl/mod.rs
+++ b/zellij-utils/src/kdl/mod.rs
@@ -5602,6 +5602,14 @@ impl UiConfig {
             let hide_default_pane_names =
                 kdl_children_property_first_arg_as_bool!(pane_frames, "hide_default_pane_names")
                     .unwrap_or(false);
+            let responsive_min_cols =
+                kdl_children_property_first_arg_as_i64!(pane_frames, "responsive_min_cols")
+                    .unwrap_or(0)
+                    .max(0) as usize;
+            let responsive_layout =
+                kdl_children_property_first_arg_as_string!(pane_frames, "responsive_layout")
+                    .unwrap_or("stacked")
+                    .to_string();
             let frame_config = FrameConfig {
                 rounded_corners,
                 hide_session_name,
@@ -5611,6 +5619,8 @@ impl UiConfig {
                 gap_aspect,
                 inactive_grayscale,
                 hide_default_pane_names,
+                responsive_min_cols,
+                responsive_layout,
             };
             ui_config.pane_frames = frame_config;
         }