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>

5 files changed, 44 insertions, 2 deletions

diff --git a/zellij-utils/src/plugin_api/action.rs b/zellij-utils/src/plugin_api/action.rs
index 5bb58db3..81db2c67 100644
--- a/zellij-utils/src/plugin_api/action.rs
+++ b/zellij-utils/src/plugin_api/action.rs
@@ -1836,7 +1836,8 @@ impl TryFrom<Action> for ProtobufAction {
             | Action::SwitchSession { .. }
             | Action::SaveSession
             | Action::ListTabs { .. }
-            | Action::CurrentTabInfo { .. } => Err("Unsupported action"),
+            | Action::CurrentTabInfo { .. }
+            | Action::SetPaneColor { .. } => Err("Unsupported action"),
         }
     }
 }
@@ -2916,6 +2917,8 @@ impl TryFrom<ProtobufTiledPaneLayout> for TiledPaneLayout {
             run_instructions_to_ignore,
             hide_floating_panes: protobuf.hide_floating_panes,
             pane_initial_contents: protobuf.pane_initial_contents,
+            default_fg: None,
+            default_bg: None,
         })
     }
 }
@@ -2972,6 +2975,8 @@ impl TryFrom<ProtobufFloatingPaneLayout> for FloatingPaneLayout {
             pane_initial_contents: protobuf.pane_initial_contents,
             logical_position: protobuf.logical_position.map(|p| p as usize),
             borderless: protobuf.borderless,
+            default_fg: None,
+            default_bg: None,
         })
     }
 }
diff --git a/zellij-utils/src/plugin_api/event.proto b/zellij-utils/src/plugin_api/event.proto
index 5aa119a9..bbee50a3 100644
--- a/zellij-utils/src/plugin_api/event.proto
+++ b/zellij-utils/src/plugin_api/event.proto
@@ -406,6 +406,8 @@ message PaneInfo {
     optional string plugin_url = 21;
     bool is_selectable = 22;
     repeated IndexInPaneGroup index_in_pane_group = 23;
+    optional string default_fg = 24;
+    optional string default_bg = 25;
 }
 
 message IndexInPaneGroup {
diff --git a/zellij-utils/src/plugin_api/event.rs b/zellij-utils/src/plugin_api/event.rs
index 3b135b6d..631d5069 100644
--- a/zellij-utils/src/plugin_api/event.rs
+++ b/zellij-utils/src/plugin_api/event.rs
@@ -1560,6 +1560,8 @@ impl TryFrom<ProtobufPaneInfo> for PaneInfo {
                     )
                 })
                 .collect(),
+            default_fg: protobuf_pane_info.default_fg,
+            default_bg: protobuf_pane_info.default_bg,
         })
     }
 }
@@ -1603,6 +1605,8 @@ impl TryFrom<PaneInfo> for ProtobufPaneInfo {
                     index: index as u32,
                 })
                 .collect(),
+            default_fg: pane_info.default_fg,
+            default_bg: pane_info.default_bg,
         })
     }
 }
@@ -2511,6 +2515,8 @@ fn serialize_session_update_event_with_non_default_values() {
             plugin_url: None,
             is_selectable: true,
             index_in_pane_group: index_in_pane_group_1,
+            default_fg: None,
+            default_bg: None,
         },
         PaneInfo {
             id: 1,
@@ -2536,6 +2542,8 @@ fn serialize_session_update_event_with_non_default_values() {
             plugin_url: Some("i_am_a_fake_plugin".to_owned()),
             is_selectable: true,
             index_in_pane_group: index_in_pane_group_2,
+            default_fg: None,
+            default_bg: None,
         },
     ];
     panes.insert(0, panes_list);
diff --git a/zellij-utils/src/plugin_api/plugin_command.proto b/zellij-utils/src/plugin_api/plugin_command.proto
index 7ba3aabe..53e9d729 100644
--- a/zellij-utils/src/plugin_api/plugin_command.proto
+++ b/zellij-utils/src/plugin_api/plugin_command.proto
@@ -198,6 +198,7 @@ enum CommandName {
   OpenEditPaneInPlaceOfPaneId = 203;
   HideFloatingPanes = 204;
   ShowFloatingPanes = 205;
+  SetPaneColor = 206;
 }
 
 message PluginCommand {
@@ -345,6 +346,7 @@ message PluginCommand {
     OpenEditPaneInPlaceOfPaneIdPayload open_edit_pane_in_place_of_pane_id_payload = 154;
     HideFloatingPanesPayload hide_floating_panes_payload = 155;
     ShowFloatingPanesPayload show_floating_panes_payload = 156;
+    SetPaneColorPayload set_pane_color_payload = 157;
   }
 }
 
@@ -1212,3 +1214,9 @@ message HideFloatingPanesResponse {
     string error = 2;
   }
 }
+
+message SetPaneColorPayload {
+  PaneId pane_id = 1;
+  optional string fg = 2;
+  optional string bg = 3;
+}
diff --git a/zellij-utils/src/plugin_api/plugin_command.rs b/zellij-utils/src/plugin_api/plugin_command.rs
index c3741591..abd9a994 100644
--- a/zellij-utils/src/plugin_api/plugin_command.rs
+++ b/zellij-utils/src/plugin_api/plugin_command.rs
@@ -102,7 +102,7 @@ pub use super::generated_api::api::{
         SaveLayoutPayload, SaveLayoutResponse as ProtobufSaveLayoutResponse, SaveSessionPayload,
         SaveSessionResponse as ProtobufSaveSessionResponse, ScrollDownInPaneIdPayload,
         ScrollToBottomInPaneIdPayload, ScrollToTopInPaneIdPayload, ScrollUpInPaneIdPayload,
-        SetFloatingPanePinnedPayload, SetPaneBorderlessPayload,
+        SetFloatingPanePinnedPayload, SetPaneBorderlessPayload, SetPaneColorPayload,
         SetSelfMouseSelectionSupportPayload, SetTimeoutPayload, ShowCursorPayload,
         ShowFloatingPanesPayload as ProtobufShowFloatingPanesPayload,
         ShowFloatingPanesResponse as ProtobufShowFloatingPanesResponse, ShowPaneWithIdPayload,
@@ -2423,6 +2423,17 @@ impl TryFrom<ProtobufPluginCommand> for PluginCommand {
                 None => Ok(PluginCommand::ShowFloatingPanes { tab_id: None }),
                 _ => Err("Mismatched payload for ShowFloatingPanes"),
             },
+            Some(CommandName::SetPaneColor) => match protobuf_plugin_command.payload {
+                Some(Payload::SetPaneColorPayload(payload)) => match payload.pane_id {
+                    Some(pane_id) => Ok(PluginCommand::SetPaneColor(
+                        pane_id.try_into()?,
+                        payload.fg,
+                        payload.bg,
+                    )),
+                    None => Err("Malformed SetPaneColor payload"),
+                },
+                _ => Err("Mismatched payload for SetPaneColor"),
+            },
             None => Err("Unrecognized plugin command"),
         }
     }
@@ -3975,6 +3986,14 @@ impl TryFrom<PluginCommand> for ProtobufPluginCommand {
                     },
                 )),
             }),
+            PluginCommand::SetPaneColor(pane_id, fg, bg) => Ok(ProtobufPluginCommand {
+                name: CommandName::SetPaneColor as i32,
+                payload: Some(Payload::SetPaneColorPayload(SetPaneColorPayload {
+                    pane_id: Some(pane_id.try_into()?),
+                    fg,
+                    bg,
+                })),
+            }),
         }
     }
 }