sl0ptty: M0 — libghostty-vt vendored, one pane, compositor, diff renderer

Design contract in DESIGN.md. libghostty-vt vendored fresh from ghostty
main@bedb6f2 (zig 0.16), built to a 14MB static lib.

M0: pty spawn (no libutil), a lib-vt terminal per pane, a screen cell buffer,
a diff emitter that repaints only what changed, raw mode, SIGWINCH, and a
~120Hz frame cap that coalesces pty reads.

Also the seed of the headless harness: --headless dumps the composited screen
without a tty, so composition is testable in milliseconds.

tests/live_m0.py covers what headless cannot: raw mode, the diff emitter,
resize propagation, and the quit path. 6/6 green.

1 files changed, 52 insertions, 0 deletions

diff --git a/vendor/libghostty-vt/src/simd/codepoint_width.zig b/vendor/libghostty-vt/src/simd/codepoint_width.zig
new file mode 100644
index 0000000..c1767be
--- /dev/null
+++ b/vendor/libghostty-vt/src/simd/codepoint_width.zig
@@ -0,0 +1,52 @@
+const std = @import("std");
+const options = @import("build_options");
+
+// vt.cpp
+extern "c" fn ghostty_simd_codepoint_width(u32) i8;
+
+pub fn codepointWidth(cp: u32) i8 {
+    if (comptime options.simd) return ghostty_simd_codepoint_width(cp);
+    const uucode = @import("uucode");
+    if (cp > uucode.config.max_code_point) return 1;
+    return @import("uucode").get(.width, @intCast(cp));
+}
+
+test "codepointWidth basic" {
+    const testing = std.testing;
+    try testing.expectEqual(@as(i8, 1), codepointWidth('a'));
+    try testing.expectEqual(@as(i8, 1), codepointWidth(0x100)); // Ā
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0x3400)); // 㐀
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0x2E3A)); // ⸺
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0x1F1E6)); // 🇦
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0x4E00)); // 一
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0xF900)); // 豈
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0x20000)); // 𠀀
+    try testing.expectEqual(@as(i8, 2), codepointWidth(0x30000)); // 𠀀
+    // try testing.expectEqual(@as(i8, 1), @import("uucode").get(.width, 0x100));
+}
+
+// This is not very fast in debug modes, so its commented by default.
+// IMPORTANT: UNCOMMENT THIS WHENEVER MAKING CODEPOINTWIDTH CHANGES.
+// test "codepointWidth matches uucode" {
+//     const testing = std.testing;
+//     const uucode = @import("uucode");
+//
+//     const min = 0xFF + 1; // start outside ascii
+//     const max = std.math.maxInt(u21) + 1;
+//     for (min..max) |cp| {
+//         const simd = codepointWidth(@intCast(cp));
+//         const uu = if (cp > uucode.config.max_code_point)
+//             1
+//         else
+//             uucode.get(.width, @intCast(cp));
+//         if (simd != uu) mismatch: {
+//             if (cp == 0x2E3B) {
+//                 try testing.expectEqual(@as(i8, 2), simd);
+//                 break :mismatch;
+//             }
+//
+//             std.log.warn("mismatch cp=U+{x} simd={} uucode={}", .{ cp, simd, uu });
+//             try testing.expect(false);
+//         }
+//     }
+// }