vt: add setopt_from_terminal to C API

Expose the key encoder Options.fromTerminal function to the C API as
ghostty_key_encoder_setopt_from_terminal. This lets C callers sync all
terminal-derived encoding options (cursor key application mode, keypad
mode, alt escape prefix, modifyOtherKeys, and Kitty flags) in a single
call instead of setting each option individually.

src/lib_vt.zig

@@ -124,6 +124,7 @@ comptime {
         @export(&c.key_encoder_new, .{ .name = "ghostty_key_encoder_new" });
         @export(&c.key_encoder_free, .{ .name = "ghostty_key_encoder_free" });
         @export(&c.key_encoder_setopt, .{ .name = "ghostty_key_encoder_setopt" });
+        @export(&c.key_encoder_setopt_from_terminal, .{ .name = "ghostty_key_encoder_setopt_from_terminal" });
         @export(&c.key_encoder_encode, .{ .name = "ghostty_key_encoder_encode" });
         @export(&c.osc_new, .{ .name = "ghostty_osc_new" });
         @export(&c.osc_free, .{ .name = "ghostty_osc_free" });

src/terminal/c/key_encode.zig

@@ -8,6 +8,7 @@ const KittyFlags = @import("../../terminal/kitty/key.zig").Flags;
 const OptionAsAlt = @import("../../input/config.zig").OptionAsAlt;
 const Result = @import("result.zig").Result;
 const KeyEvent = @import("key_event.zig").Event;
+const Terminal = @import("terminal.zig").Terminal;
 
 const log = std.log.scoped(.key_encode);
 
@@ -115,6 +116,15 @@ fn setoptTyped(
     }
 }
 
+pub fn setopt_from_terminal(
+    encoder_: Encoder,
+    terminal_: Terminal,
+) callconv(.c) void {
+    const wrapper = encoder_ orelse return;
+    const t = terminal_ orelse return;
+    wrapper.opts = .fromTerminal(t);
+}
+
 pub fn encode(
     encoder_: Encoder,
     event_: KeyEvent,
@@ -222,6 +232,64 @@ test "setopt macos option as alt" {
     try testing.expectEqual(OptionAsAlt.true, e.?.opts.macos_option_as_alt);
 }
 
+test "setopt_from_terminal" {
+    const testing = std.testing;
+    const terminal_c = @import("terminal.zig");
+
+    // Create encoder
+    var e: Encoder = undefined;
+    try testing.expectEqual(Result.success, new(
+        &lib_alloc.test_allocator,
+        &e,
+    ));
+    defer free(e);
+
+    // Create terminal
+    var t: Terminal = undefined;
+    try testing.expectEqual(Result.success, terminal_c.new(
+        &lib_alloc.test_allocator,
+        &t,
+        .{ .cols = 80, .rows = 24, .max_scrollback = 0 },
+    ));
+    defer terminal_c.free(t);
+
+    // Apply terminal state to encoder
+    setopt_from_terminal(e, t);
+
+    // Options should reflect defaults from a fresh terminal
+    try testing.expect(!e.?.opts.cursor_key_application);
+    try testing.expect(!e.?.opts.alt_esc_prefix);
+    try testing.expectEqual(KittyFlags.disabled, e.?.opts.kitty_flags);
+    try testing.expectEqual(OptionAsAlt.false, e.?.opts.macos_option_as_alt);
+}
+
+test "setopt_from_terminal null" {
+    // Both null should be no-ops
+    setopt_from_terminal(null, null);
+
+    const testing = std.testing;
+
+    // Encoder null with valid terminal
+    const terminal_c = @import("terminal.zig");
+    var t: Terminal = undefined;
+    try testing.expectEqual(Result.success, terminal_c.new(
+        &lib_alloc.test_allocator,
+        &t,
+        .{ .cols = 80, .rows = 24, .max_scrollback = 0 },
+    ));
+    defer terminal_c.free(t);
+    setopt_from_terminal(null, t);
+
+    // Valid encoder with null terminal
+    var e: Encoder = undefined;
+    try testing.expectEqual(Result.success, new(
+        &lib_alloc.test_allocator,
+        &e,
+    ));
+    defer free(e);
+    setopt_from_terminal(e, null);
+}
+
 test "encode: kitty ctrl release with ctrl mod set" {
     const testing = std.testing;
 

src/terminal/c/main.zig

@@ -55,6 +55,7 @@ pub const key_event_get_unshifted_codepoint = key_event.get_unshifted_codepoint;
 pub const key_encoder_new = key_encode.new;
 pub const key_encoder_free = key_encode.free;
 pub const key_encoder_setopt = key_encode.setopt;
+pub const key_encoder_setopt_from_terminal = key_encode.setopt_from_terminal;
 pub const key_encoder_encode = key_encode.encode;
 
 pub const paste_is_safe = paste.is_safe;