show names on tabs in tabbed layout

src/Window.zig

@@ -137,6 +137,15 @@ pub fn applyRules(self: *Window) void {
     }
 }
 
+/// Whether this window currently has a tab drawn for it, i.e. it is tiled and
+/// visible on an output that is showing the tabbed layout.
+fn onTabBar(self: *Window) bool {
+    if (config.tabbar_height <= 0) return false;
+    if (!self.visible or self.floating or self.fullscreen or self.closed) return false;
+    const out = self.output orelse return false;
+    return out.state().layout == .tabbed;
+}
+
 fn setString(self: *Window, field: *?[]u8, value: ?[*:0]const u8) void {
     const gpa = self.wm.gpa;
     if (field.*) |old| gpa.free(old);
@@ -190,6 +199,10 @@ fn onEvent(_: *river.WindowV1, event: river.WindowV1.Event, self: *Window) void
             self.setString(&self.title, ev.title);
             self.applyRules();
             self.wm.ipcDirty();
+            // The tab bar has this title painted into it, so a window that is
+            // wearing a tab needs the strip redrawn. Terminals retitle
+            // themselves constantly, so ask only when it will show.
+            if (self.onTabBar()) self.wm.needsManage();
         },
 
         .identifier => |ev| {