termio: report color scheme synchronously

The reporting of color scheme was handled asynchronously by queuing a
handler in the surface. This could lead to race conditions where the
DSR is reported after subsequent VT sequences.

Fixes #5922

src/Surface.zig

@@ -1023,8 +1023,6 @@ pub fn handleMessage(self: *Surface, msg: Message) !void {
 
         .scrollbar => |scrollbar| self.updateScrollbar(scrollbar),
 
-        .report_color_scheme => |force| self.reportColorScheme(force),
-
         .present_surface => try self.presentSurface(),
 
         .password_input => |v| try self.passwordInput(v),
@@ -1336,16 +1334,12 @@ fn passwordInput(self: *Surface, v: bool) !void {
     try self.queueRender();
 }
 
-/// Sends a DSR response for the current color scheme to the pty. If
-/// force is false then we only send the response if the terminal mode
-/// 2031 is enabled.
-fn reportColorScheme(self: *Surface, force: bool) void {
-    if (!force) {
-        self.renderer_state.mutex.lock();
-        defer self.renderer_state.mutex.unlock();
-        if (!self.renderer_state.terminal.modes.get(.report_color_scheme)) {
-            return;
-        }
+/// Sends a DSR response for the current color scheme to the pty.
+fn reportColorScheme(self: *Surface) void {
+    self.renderer_state.mutex.lock();
+    defer self.renderer_state.mutex.unlock();
+    if (!self.renderer_state.terminal.modes.get(.report_color_scheme)) {
+        return;
     }
 
     const output = switch (self.config_conditional_state.theme) {
@@ -4772,7 +4766,7 @@ pub fn colorSchemeCallback(self: *Surface, scheme: apprt.ColorScheme) !void {
     self.notifyConfigConditionalState();
 
     // If mode 2031 is on, then we report the change live.
-    self.reportColorScheme(false);
+    self.reportColorScheme();
 }
 
 pub fn posToViewport(self: Surface, xpos: f64, ypos: f64) terminal.point.Coordinate {

src/apprt/surface.zig

@@ -63,11 +63,6 @@ pub const Message = union(enum) {
     /// Health status change for the renderer.
     renderer_health: renderer.Health,
 
-    /// Report the color scheme. The bool parameter is whether to force or not.
-    /// If force is true, the color scheme should be reported even if mode
-    /// 2031 is not set.
-    report_color_scheme: bool,
-
     /// Tell the surface to present itself to the user. This may require raising
     /// a window and switching tabs.
     present_surface: void,

src/termio/Termio.zig

@@ -162,6 +162,7 @@ pub const DerivedConfig = struct {
     osc_color_report_format: configpkg.Config.OSCColorReportFormat,
     clipboard_write: configpkg.ClipboardAccess,
     enquiry_response: []const u8,
+    conditional_state: configpkg.ConditionalState,
 
     pub fn init(
         alloc_gpa: Allocator,
@@ -182,6 +183,7 @@ pub const DerivedConfig = struct {
             .osc_color_report_format = config.@"osc-color-report-format",
             .clipboard_write = config.@"clipboard-write",
             .enquiry_response = try alloc.dupe(u8, config.@"enquiry-response"),
+            .conditional_state = config._conditional_state,
 
             // This has to be last so that we copy AFTER the arena allocations
             // above happen (Zig assigns in order).
@@ -276,6 +278,7 @@ pub fn init(self: *Termio, alloc: Allocator, opts: termio.Options) !void {
         .enquiry_response = opts.config.enquiry_response,
         .default_cursor_style = opts.config.cursor_style,
         .default_cursor_blink = opts.config.cursor_blink,
+        .config_conditional_state = opts.config.conditional_state,
     };
 
     const thread_enter_state = try ThreadEnterState.create(

src/termio/stream_handler.zig

@@ -53,6 +53,9 @@ pub const StreamHandler = struct {
     /// The color reporting format for OSC requests.
     osc_color_report_format: configpkg.Config.OSCColorReportFormat,
 
+    /// The config conditional state.
+    config_conditional_state: configpkg.ConditionalState,
+
     /// The clipboard write access configuration.
     clipboard_write: configpkg.ClipboardAccess,
 
@@ -100,6 +103,7 @@ pub const StreamHandler = struct {
         self.enquiry_response = config.enquiry_response;
         self.default_cursor_style = config.cursor_style;
         self.default_cursor_blink = config.cursor_blink;
+        self.config_conditional_state = config.conditional_state;
 
         // If our cursor is the default, then we update it immediately.
         if (self.default_cursor) self.setCursorStyle(.default) catch |err| {
@@ -107,7 +111,7 @@ pub const StreamHandler = struct {
         };
 
         // The config could have changed any of our colors so update mode 2031
-        self.surfaceMessageWriter(.{ .report_color_scheme = false });
+        self.reportColorScheme(false);
     }
 
     inline fn surfaceMessageWriter(
@@ -790,10 +794,23 @@ pub const StreamHandler = struct {
                 self.messageWriter(msg);
             },
 
-            .color_scheme => self.surfaceMessageWriter(.{ .report_color_scheme = true }),
+            .color_scheme => self.reportColorScheme(true),
         }
     }
 
+    /// Sends a DSR response for the current color scheme to the pty.
+    /// The caller is resposible for holding self.renderer_state.mutex.
+    pub fn reportColorScheme(self: *StreamHandler, force: bool) void {
+        if (!force and !self.renderer_state.terminal.modes.get(.report_color_scheme)) {
+            return;
+        }
+        const output = switch (self.config_conditional_state.theme) {
+            .light => "\x1B[?997;2n",
+            .dark => "\x1B[?997;1n",
+        };
+        self.messageWriter(.{ .write_stable = output });
+    }
+
     pub fn setCursorStyle(
         self: *StreamHandler,
         style: terminal.CursorStyleReq,
@@ -875,7 +892,7 @@ pub const StreamHandler = struct {
         try self.setMouseShape(.text);
 
         // Reset resets our palette so we report it for mode 2031.
-        self.surfaceMessageWriter(.{ .report_color_scheme = false });
+        self.reportColorScheme(false);
     }
 
     pub fn queryKittyKeyboard(self: *StreamHandler) !void {