feat(terminal): enable SIMD acceleration for ghostty VT parsing

- Build ghostty's C++ SIMD implementation (vt.cpp) using highway
- Configure simdutf via webkit wrapper header
- Add utfcpp dependency for UTF-8 error handling with replacement chars
- Enable exceptions for vt.cpp only (required by utfcpp)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

cmake/targets/BuildGhosttyVt.cmake

@@ -18,5 +18,58 @@ register_repository(
     v1.1.3
 )
 
+# utfcpp - header-only UTF-8 library for error handling in SIMD code
+register_repository(
+  NAME
+    utfcpp
+  REPOSITORY
+    nemtrif/utfcpp
+  TAG
+    v4.0.5
+)
+
 # The ghostty source is cloned to ${VENDOR_PATH}/ghostty
 # Bun's build.zig will reference it directly as a Zig module
+
+# Build the SIMD acceleration library for ghostty
+# This provides optimized UTF-8 decoding for terminal escape sequence parsing
+set(GHOSTTY_SIMD_SRC ${VENDOR_PATH}/ghostty/src/simd/vt.cpp)
+
+add_library(ghostty-simd STATIC ${GHOSTTY_SIMD_SRC})
+
+target_include_directories(ghostty-simd PRIVATE
+  # Bun's compatibility headers (simdutf.h wrapper)
+  ${CWD}/src/deps/ghostty
+  # Ghostty's own headers
+  ${VENDOR_PATH}/ghostty/src
+  # Highway SIMD library (from Bun's vendor)
+  ${BUILD_PATH}/highway
+  ${VENDOR_PATH}/highway
+  # simdutf from webkit
+  ${WEBKIT_INCLUDE_PATH}
+  ${WEBKIT_INCLUDE_PATH}/wtf
+  # utfcpp for UTF-8 error handling
+  ${VENDOR_PATH}/utfcpp/source
+)
+
+target_compile_definitions(ghostty-simd PRIVATE
+  # Highway configuration
+  HWY_STATIC_DEFINE
+)
+
+# Enable exceptions for this file only - utfcpp's replace_invalid uses them
+set_source_files_properties(${GHOSTTY_SIMD_SRC} PROPERTIES
+  COMPILE_FLAGS "-fexceptions"
+)
+
+# Ensure dependencies are built first
+add_dependencies(ghostty-simd clone-ghostty clone-utfcpp)
+if(TARGET highway)
+  add_dependencies(ghostty-simd highway)
+endif()
+
+# Link ghostty-simd into bun
+target_link_libraries(${bun} PRIVATE ghostty-simd)
+
+# Link highway library
+target_link_libraries(${bun} PRIVATE ${BUILD_PATH}/highway/libhwy.a)

src/deps/ghostty/build_options.zig

@@ -2,8 +2,6 @@
 //! This provides the build_options that ghostty's SIMD code expects.
 
 /// SIMD acceleration for optimized UTF-8 and escape sequence parsing.
-/// Currently disabled because ghostty's SIMD uses C++ implementations (vt.cpp)
-/// that would need to be built and linked separately.
-/// The scalar fallback paths provide correct functionality.
+/// Uses highway SIMD library with simdutf for fast UTF-8 decoding.
 /// Note: Keep in sync with terminal_options.simd
-pub const simd = false;
+pub const simd = true;

src/deps/ghostty/simdutf.h

@@ -0,0 +1,5 @@
+// Wrapper header to include simdutf from webkit
+// ghostty's vt.cpp expects <simdutf.h> but Bun provides it via webkit
+#pragma once
+
+#include <wtf/SIMDUTF.h>

src/deps/ghostty/terminal_options.zig

@@ -16,10 +16,8 @@ pub const c_abi = false;
 pub const oniguruma = false;
 
 /// SIMD acceleration for optimized UTF-8 and escape sequence parsing.
-/// Currently disabled because ghostty's SIMD uses C++ implementations (vt.cpp)
-/// that would need to be built and linked separately.
-/// The scalar fallback paths provide correct functionality.
-pub const simd = false;
+/// Uses highway SIMD library with simdutf for fast UTF-8 decoding.
+pub const simd = true;
 
 /// Slow runtime safety checks - disabled in production
 pub const slow_runtime_safety = false;