feat: add per-pane default foreground/background color support (#4737)

* feat: add per-pane default foreground/background color support

Add per-pane default foreground and background colors, configurable
through four surfaces:

- OSC 10/11 escape sequences (set/query) and OSC 110/111 (reset)
- CLI action: zellij action set-pane-color --pane-id <id> --fg/--bg
- Layout config: default_fg/default_bg properties on pane nodes
- Plugin API: set_pane_color() SDK function and PaneInfo read-side

Colors are applied at render time as a fallback when cells have no
explicit foreground/background, without mutating stored grid data.

Closes #4712

* refactor: address review feedback for pane color support

- Extract adjust_styles_for_custom_bg_fg in output/mod.rs
- Move color parsing (xparse_color) from tab into Grid
- Move color serialization (ansi_code_to_color_string) into Grid
- Pane trait now uses Option<String> for color getters/setters
- Add colors to session serialization (dump-layout)
- Add default_fg/default_bg to protobuf IPC schema to fix
  layout-in-session color loss
- Update example layout with tab-bar and status-bar

* fix stack overflow and ordering

* rustfmt

* update e2e snapshots

---------

Co-authored-by: Karl Bunch <karl@karlbunch.com>
Co-authored-by: Aram Drevekenin <aram@poor.dev>

2 files changed, 22 insertions, 0 deletions

diff --git a/zellij-utils/src/kdl/kdl_layout_parser.rs b/zellij-utils/src/kdl/kdl_layout_parser.rs
index 6e1e2c76..ff7fcfe3 100644
--- a/zellij-utils/src/kdl/kdl_layout_parser.rs
+++ b/zellij-utils/src/kdl/kdl_layout_parser.rs
@@ -106,6 +106,8 @@ impl<'a> KdlLayoutParser<'a> {
             || property_name == "expanded"
             || property_name == "exclude_from_sync"
             || property_name == "contents_file"
+            || property_name == "default_fg"
+            || property_name == "default_bg"
     }
     fn is_a_valid_floating_pane_property(&self, property_name: &str) -> bool {
         property_name == "borderless"
@@ -124,6 +126,8 @@ impl<'a> KdlLayoutParser<'a> {
             || property_name == "height"
             || property_name == "pinned"
             || property_name == "contents_file"
+            || property_name == "default_fg"
+            || property_name == "default_bg"
     }
     fn is_a_valid_tab_property(&self, property_name: &str) -> bool {
         property_name == "focus"
@@ -563,6 +567,10 @@ impl<'a> KdlLayoutParser<'a> {
                 kdl_node.span().len(),
             ));
         }
+        let default_fg = kdl_get_string_property_or_child_value_with_error!(kdl_node, "default_fg")
+            .map(|s| s.to_string());
+        let default_bg = kdl_get_string_property_or_child_value_with_error!(kdl_node, "default_bg")
+            .map(|s| s.to_string());
         self.assert_no_mixed_children_and_properties(kdl_node)?;
         let pane_initial_contents = contents_file.and_then(|contents_file| {
             self.file_name
@@ -585,6 +593,8 @@ impl<'a> KdlLayoutParser<'a> {
             children_are_stacked,
             is_expanded_in_stack,
             pane_initial_contents,
+            default_fg,
+            default_bg,
             ..Default::default()
         })
     }
@@ -605,6 +615,10 @@ impl<'a> KdlLayoutParser<'a> {
             .map(|name| name.to_string());
         let contents_file =
             kdl_get_string_property_or_child_value_with_error!(kdl_node, "contents_file");
+        let default_fg = kdl_get_string_property_or_child_value_with_error!(kdl_node, "default_fg")
+            .map(|s| s.to_string());
+        let default_bg = kdl_get_string_property_or_child_value_with_error!(kdl_node, "default_bg")
+            .map(|s| s.to_string());
         self.assert_no_mixed_children_and_properties(kdl_node)?;
         let pane_initial_contents = contents_file.and_then(|contents_file| {
             self.file_name
@@ -625,6 +639,8 @@ impl<'a> KdlLayoutParser<'a> {
             pinned,
             borderless,
             pane_initial_contents,
+            default_fg,
+            default_bg,
             ..Default::default()
         })
     }
diff --git a/zellij-utils/src/kdl/mod.rs b/zellij-utils/src/kdl/mod.rs
index 12eadff6..9fcb3113 100644
--- a/zellij-utils/src/kdl/mod.rs
+++ b/zellij-utils/src/kdl/mod.rs
@@ -5927,6 +5927,8 @@ impl PaneInfo {
             plugin_url,
             is_selectable,
             index_in_pane_group: Default::default(), // we don't serialize this
+            default_fg: None,
+            default_bg: None,
         };
         Ok((tab_position, pane_info))
     }
@@ -6075,6 +6077,8 @@ fn serialize_and_deserialize_session_info_with_data() {
             plugin_url: None,
             is_selectable: true,
             index_in_pane_group: Default::default(), // we don't serialize this
+            default_fg: None,
+            default_bg: None,
         },
         PaneInfo {
             id: 1,
@@ -6100,6 +6104,8 @@ fn serialize_and_deserialize_session_info_with_data() {
             plugin_url: Some("i_am_a_fake_plugin".to_owned()),
             is_selectable: true,
             index_in_pane_group: Default::default(), // we don't serialize this
+            default_fg: None,
+            default_bg: None,
         },
     ];
     let mut panes = HashMap::new();