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, 79 insertions, 0 deletions

diff --git a/vendor/libghostty-vt/pkg/highway/src/cpp/targets.cpp b/vendor/libghostty-vt/pkg/highway/src/cpp/targets.cpp
new file mode 100644
index 0000000..7977cd5
--- /dev/null
+++ b/vendor/libghostty-vt/pkg/highway/src/cpp/targets.cpp
@@ -0,0 +1,79 @@
+// Vendored from google/highway hwy/targets.cc at commit:
+// 66486a10623fa0d72fe91260f96c892e41aceb06
+//
+// Local modifications:
+// - Dropped upstream CPU feature probing and platform-specific detection code
+//   in favor of Ghostty's Zig-provided ghostty_hwy_detect_targets().
+// - Removed the HWY_WARN baseline-mismatch diagnostic path so this file does
+//   not depend on libc-backed formatting/logging.
+// - Kept only the chosen-target bookkeeping and runtime dispatch state that
+//   Highway's HWY_DYNAMIC_DISPATCH machinery needs.
+// - Added hwy_supported_targets() as a small C shim for Zig to query the final
+//   supported target mask.
+//
+// Why:
+// - Ghostty wants a minimal vendored Highway runtime that avoids direct libc
+//   usage and lets Zig own target detection policy.
+// - Narrowing this file to dispatch state makes the local fork easier to audit
+//   and maintain than carrying upstream's full platform detection surface.
+
+#include "hwy/targets.h"
+
+namespace hwy {
+
+extern "C" int64_t ghostty_hwy_detect_targets();
+
+// Vendored from Highway's hwy/targets.cc. Ghostty provides target detection in
+// Zig, so this TU only retains the runtime dispatch/chosen-target state.
+static int64_t DetectTargets() {
+  int64_t bits = HWY_SCALAR | HWY_EMU128;
+
+#if (HWY_ARCH_X86 || HWY_ARCH_ARM || HWY_ARCH_PPC || HWY_ARCH_S390X || \
+     HWY_ARCH_RISCV || HWY_ARCH_LOONGARCH) && \
+    HWY_HAVE_RUNTIME_DISPATCH
+  bits |= ghostty_hwy_detect_targets();
+#else
+  bits |= HWY_ENABLED_BASELINE;
+#endif
+
+  return bits;
+}
+
+// When running tests, this value can be set to the mocked supported targets
+// mask. Only written to from a single thread before the test starts.
+static int64_t supported_targets_for_test_ = 0;
+
+// Mask of targets disabled at runtime with DisableTargets.
+static int64_t supported_mask_ = LimitsMax<int64_t>();
+
+HWY_DLLEXPORT void DisableTargets(int64_t disabled_targets) {
+  supported_mask_ = static_cast<int64_t>(~disabled_targets);
+  GetChosenTarget().DeInit();
+}
+
+HWY_DLLEXPORT void SetSupportedTargetsForTest(int64_t targets) {
+  supported_targets_for_test_ = targets;
+  GetChosenTarget().DeInit();
+}
+
+HWY_DLLEXPORT int64_t SupportedTargets() {
+  int64_t targets = supported_targets_for_test_;
+  if (HWY_LIKELY(targets == 0)) {
+    targets = DetectTargets();
+    GetChosenTarget().Update(targets);
+  }
+
+  targets &= supported_mask_;
+  return targets == 0 ? HWY_STATIC_TARGET : targets;
+}
+
+HWY_DLLEXPORT ChosenTarget& GetChosenTarget() {
+  static ChosenTarget chosen_target;
+  return chosen_target;
+}
+
+}  // namespace hwy
+
+extern "C" int64_t hwy_supported_targets() {
+  return hwy::SupportedTargets();
+}