config: control cgroup isolation

src/config/Config.zig

@@ -988,6 +988,30 @@ keybind: Keybinds = .{},
 /// This does not work with GLFW builds.
 @"macos-option-as-alt": OptionAsAlt = .false,
 
+/// Put every surface (tab, split, window) into a dedicated Linux cgroup.
+///
+/// This makes it so that resource management can be done on a per-surface
+/// granularity. For example, if a shell program is using too much memory,
+/// only that shell will be killed by the oom monitor instead of the entire
+/// Ghostty process. Similarly, if a shell program is using too much CPU,
+/// only that surface will be CPU-throttled.
+///
+/// This will cause startup times to be slower (a hundred milliseconds or so),
+/// so the default value is "single-instance." In single-instance mode, only
+/// one instance of Ghostty is running (see gtk-single-instance) so the startup
+/// time is a one-time cost. Additionally, single instance Ghostty is much
+/// more likely to have many windows, tabs, etc. so cgroup isolation is a
+/// big benefit.
+///
+/// Valid values are:
+///
+///   * `never` - Never use cgroups.
+///   * `always` - Always use cgroups.
+///   * `single-instance` - Enable cgroups only for Ghostty instances launched
+///     as single-instance applications (see gtk-single-instance).
+///
+@"linux-cgroup": LinuxCgroup = .@"single-instance",
+
 /// If true, the Ghostty GTK application will run in single-instance mode:
 /// each new `ghostty` process launched will result in a new window if there
 /// is already a running process.
@@ -3495,3 +3519,10 @@ pub const GraphemeWidthMethod = enum {
     legacy,
     unicode,
 };
+
+/// See linux-cgroup
+pub const LinuxCgroup = enum {
+    never,
+    always,
+    @"single-instance",
+};