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, 7 insertions, 0 deletions

diff --git a/vendor/libghostty-vt/include/module.modulemap b/vendor/libghostty-vt/include/module.modulemap
new file mode 100644
index 0000000..8961f5c
--- /dev/null
+++ b/vendor/libghostty-vt/include/module.modulemap
@@ -0,0 +1,7 @@
+// This makes Ghostty available to the XCode build for the macOS app.
+// We append "Kit" to it not to be cute, but because targets have to have
+// unique names and we use Ghostty for other things.
+module GhosttyKit {
+    umbrella header "ghostty.h"
+    export *
+}