core: add 64 bit unique ID to every core surface (#12027)

- Expose that ID as the environment variable GHOSTTY_SURFACE_ID to
processes running in Ghostty surfaces.
- Add a function to the core app to search for surfaces by ID.
- ID is randomly generated, it has no other meaning other than as a
unique identifier for the surface. The ID also cannot be zero as that is
used to indicate a null ID in some situations.

src/App.zig

@@ -524,6 +524,16 @@ fn hasSurface(self: *const App, surface: *const Surface) bool {
     return false;
 }
 
+/// Search for a surface by a 64 bit unique ID.
+pub fn findSurfaceByID(self: *const App, id: u64) ?*Surface {
+    for (self.surfaces.items) |v| {
+        const surface: *Surface = v.core();
+        if (surface.id == id) return surface;
+    }
+
+    return null;
+}
+
 fn hasRtSurface(self: *const App, surface: *apprt.Surface) bool {
     for (self.surfaces.items) |v| {
         if (v == surface) return true;

src/Surface.zig

@@ -54,6 +54,13 @@ pub const min_window_height_cells: u32 = 4;
 /// given time. `activate_key_table` calls after this are ignored.
 const max_active_key_tables = 8;
 
+/// Unique ID used to identify this surface for IPC purposes. It is
+/// exposed to the commands running in surfaces as the environment variable
+/// GHOSTTY_SURFACE_ID. It must not be zero as zero is used to incicate a null
+/// value when communicating an ID over DBus as DBus does not allow null/maybe
+/// values.
+id: u64,
+
 /// Allocator
 alloc: Allocator,
 
@@ -579,6 +586,13 @@ pub fn init(
     errdefer io_thread.deinit();
 
     self.* = .{
+        .id = id: {
+            while (true) {
+                const candidate = std.crypto.random.int(u64);
+                if (candidate == 0) continue;
+                break :id candidate;
+            }
+        },
         .alloc = alloc,
         .app = app,
         .rt_app = rt_app,
@@ -632,6 +646,12 @@ pub fn init(
         // don't leak GHOSTTY_LOG to any subprocesses
         env.remove("GHOSTTY_LOG");
 
+        var buf: [18]u8 = undefined;
+        try env.put(
+            "GHOSTTY_SURFACE_ID",
+            std.fmt.bufPrint(&buf, "0x{x:0>16}", .{self.id}) catch unreachable,
+        );
+
         // Initialize our IO backend
         var io_exec = try termio.Exec.init(alloc, .{
             .command = command,