libghostty: expose get/set active selection state

Add terminal set/get support for the active screen selection through the
existing option and data APIs. Setting a selection copies the C snapshot
into terminal-owned tracked state, while passing NULL clears the current
selection.

Getting the selection now returns an untracked GhosttySelection snapshot
or GHOSTTY_NO_VALUE when there is no selection. The C header documents
the different lifetimes for set and get so embedders know when input and
returned grid references remain valid.

include/ghostty/vt/terminal.h

@@ -19,6 +19,7 @@
 #include <ghostty/vt/kitty_graphics.h>
 #include <ghostty/vt/screen.h>
 #include <ghostty/vt/point.h>
+#include <ghostty/vt/selection.h>
 #include <ghostty/vt/style.h>
 
 #ifdef __cplusplus
@@ -592,6 +593,21 @@ typedef enum GHOSTTY_ENUM_TYPED {
    * Input type: size_t*
    */
   GHOSTTY_TERMINAL_OPT_APC_MAX_BYTES_KITTY = 20,
+
+  /**
+   * Set the active screen selection.
+   *
+   * The value must point to a GhosttySelection whose grid references are
+   * valid for this terminal's active screen at the time of the call. The
+   * terminal copies the selection immediately and converts it to
+   * terminal-owned tracked state, so the GhosttySelection struct and its
+   * untracked grid references do not need to outlive this call.
+   *
+   * Passing NULL clears the active screen selection.
+   *
+   * Input type: GhosttySelection*
+   */
+  GHOSTTY_TERMINAL_OPT_SELECTION = 21,
   GHOSTTY_TERMINAL_OPT_MAX_VALUE = GHOSTTY_ENUM_MAX_VALUE,
 } GhosttyTerminalOption;
 
@@ -868,6 +884,23 @@ typedef enum GHOSTTY_ENUM_TYPED {
    * Output type: GhosttyKittyGraphics *
    */
   GHOSTTY_TERMINAL_DATA_KITTY_GRAPHICS = 30,
+
+  /**
+   * The active screen's current selection.
+   *
+   * On success, writes an untracked snapshot of the terminal-owned selection
+   * to the caller-provided GhosttySelection. The GhosttySelection struct is
+   * caller-owned and may be kept, but the grid references inside it are
+   * untracked borrowed references into the active screen. They are only valid
+   * until the next mutating terminal call, such as ghostty_terminal_set(),
+   * ghostty_terminal_vt_write(), ghostty_terminal_resize(), or
+   * ghostty_terminal_reset().
+   *
+   * Returns GHOSTTY_NO_VALUE when there is no active selection.
+   *
+   * Output type: GhosttySelection *
+   */
+  GHOSTTY_TERMINAL_DATA_SELECTION = 31,
   GHOSTTY_TERMINAL_DATA_MAX_VALUE = GHOSTTY_ENUM_MAX_VALUE,
 } GhosttyTerminalData;
 

src/terminal/c/selection.zig

@@ -13,4 +13,12 @@ pub const CSelection = extern struct {
         const end_pin = self.end.toPin() orelse return null;
         return Selection.init(start_pin, end_pin, self.rectangle);
     }
+
+    pub fn fromZig(sel: Selection) CSelection {
+        return .{
+            .start = .fromPin(sel.start()),
+            .end = .fromPin(sel.end()),
+            .rectangle = sel.rectangle,
+        };
+    }
 };

src/terminal/c/terminal.zig

@@ -20,6 +20,7 @@ const cell_c = @import("cell.zig");
 const row_c = @import("row.zig");
 const grid_ref_c = @import("grid_ref.zig");
 const grid_ref_tracked_c = @import("grid_ref_tracked.zig");
+const selection_c = @import("selection.zig");
 const style_c = @import("style.zig");
 const color = @import("../color.zig");
 const Result = @import("result.zig").Result;
@@ -314,6 +315,7 @@ pub const Option = enum(c_int) {
     kitty_image_medium_shared_mem = 18,
     apc_max_bytes = 19,
     apc_max_bytes_kitty = 20,
+    selection = 21,
 
     /// Input type expected for setting the option.
     pub fn InType(comptime self: Option) type {
@@ -336,6 +338,7 @@ pub const Option = enum(c_int) {
             .kitty_image_medium_shared_mem,
             => ?*const bool,
             .apc_max_bytes, .apc_max_bytes_kitty => ?*const usize,
+            .selection => ?*const selection_c.CSelection,
         };
     }
 };
@@ -443,6 +446,14 @@ fn setTyped(
                 wrapper.stream.handler.apc_handler.max_bytes.remove(.kitty);
             }
         },
+        .selection => {
+            if (value) |ptr| {
+                const sel = ptr.toZig() orelse return .invalid_value;
+                wrapper.terminal.screens.active.select(sel) catch return .out_of_memory;
+            } else {
+                wrapper.terminal.screens.active.clearSelection();
+            }
+        },
     }
     return .success;
 }
@@ -576,6 +587,7 @@ pub const TerminalData = enum(c_int) {
     kitty_image_medium_temp_file = 28,
     kitty_image_medium_shared_mem = 29,
     kitty_graphics = 30,
+    selection = 31,
 
     /// Output type expected for querying the data of the given kind.
     pub fn OutType(comptime self: TerminalData) type {
@@ -604,6 +616,7 @@ pub const TerminalData = enum(c_int) {
             .kitty_image_medium_shared_mem,
             => bool,
             .kitty_graphics => KittyGraphics,
+            .selection => selection_c.CSelection,
         };
     }
 };
@@ -713,6 +726,9 @@ fn getTyped(
             if (comptime !build_options.kitty_graphics) return .no_value;
             out.* = &t.screens.active.kitty_images;
         },
+        .selection => out.* = selection_c.CSelection.fromZig(
+            t.screens.active.selection orelse return .no_value,
+        ),
     }
 
     return .success;
@@ -1325,6 +1341,54 @@ test "get invalid" {
     try testing.expectEqual(Result.invalid_value, get(t, .invalid, null));
 }
 
+test "set and get selection" {
+    var t: Terminal = null;
+    try testing.expectEqual(Result.success, new(
+        &lib.alloc.test_allocator,
+        &t,
+        .{
+            .cols = 80,
+            .rows = 24,
+            .max_scrollback = 0,
+        },
+    ));
+    defer free(t);
+
+    vt_write(t, "Hello", 5);
+
+    var start_ref: grid_ref_c.CGridRef = .{};
+    try testing.expectEqual(Result.success, grid_ref(t, .{
+        .tag = .active,
+        .value = .{ .active = .{ .x = 0, .y = 0 } },
+    }, &start_ref));
+
+    var end_ref: grid_ref_c.CGridRef = .{};
+    try testing.expectEqual(Result.success, grid_ref(t, .{
+        .tag = .active,
+        .value = .{ .active = .{ .x = 4, .y = 0 } },
+    }, &end_ref));
+
+    var out: selection_c.CSelection = undefined;
+    try testing.expectEqual(Result.no_value, get(t, .selection, @ptrCast(&out)));
+
+    const sel: selection_c.CSelection = .{
+        .start = start_ref,
+        .end = end_ref,
+        .rectangle = true,
+    };
+    try testing.expectEqual(Result.success, set(t, .selection, @ptrCast(&sel)));
+    try testing.expect(t.?.terminal.screens.active.selection.?.tracked());
+
+    try testing.expectEqual(Result.success, get(t, .selection, @ptrCast(&out)));
+    try testing.expect(out.start.toPin().?.eql(start_ref.toPin().?));
+    try testing.expect(out.end.toPin().?.eql(end_ref.toPin().?));
+    try testing.expect(out.rectangle);
+
+    try testing.expectEqual(Result.success, set(t, .selection, null));
+    try testing.expect(t.?.terminal.screens.active.selection == null);
+    try testing.expectEqual(Result.no_value, get(t, .selection, @ptrCast(&out)));
+}
+
 test "grid_ref" {
     var t: Terminal = null;
     try testing.expectEqual(Result.success, new(