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, 32 insertions, 0 deletions

diff --git a/vendor/libghostty-vt/src/os/kernel_info.zig b/vendor/libghostty-vt/src/os/kernel_info.zig
new file mode 100644
index 0000000..60e6b49
--- /dev/null
+++ b/vendor/libghostty-vt/src/os/kernel_info.zig
@@ -0,0 +1,32 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const global = @import("../global.zig");
+
+pub fn getKernelInfo(alloc: std.mem.Allocator) ?[]const u8 {
+    if (comptime builtin.os.tag != .linux) return null;
+    const path = "/proc/sys/kernel/osrelease";
+    var file = std.Io.Dir.openFileAbsolute(global.io(), path, .{}) catch return null;
+    defer file.close(global.io());
+
+    // 128 bytes should be enough to hold the kernel information
+    var kernel_info_buf: [128]u8 = undefined;
+    const kernel_info = kernel_info_buf[0 .. file.readPositionalAll(
+        global.io(),
+        &kernel_info_buf,
+        0,
+    ) catch return null];
+    return alloc.dupe(u8, std.mem.trim(u8, kernel_info, &std.ascii.whitespace)) catch return null;
+}
+
+test "read /proc/sys/kernel/osrelease" {
+    if (comptime builtin.os.tag != .linux) return null;
+    const allocator = std.testing.allocator;
+
+    const kernel_info = getKernelInfo(allocator).?;
+    defer allocator.free(kernel_info);
+
+    // Since we can't hardcode the info in tests, just check
+    // if something was read from the file
+    try std.testing.expect(kernel_info.len > 0);
+    try std.testing.expect(!std.mem.eql(u8, kernel_info, ""));
+}