Fix #155: fix wasm builds (#156)

* Fix #155: switch WASM builds from legacy Asyncify to JSPI

cmake/Emscripten.cmake set both -fwasm-exceptions (compile + link) and
-sASYNCIFY=1 (per-target link), and recent emsdk releases hard-fail the
combination in wasm-opt with `__asyncify_get_call_index does not exist`,
breaking the wasm.yml workflow. JSPI (JavaScript Promise Integration) is
the upstream-recommended replacement for legacy Asyncify and is
compatible with native WebAssembly exception handling, so the per-target
flag now reads -sJSPI=1 and the no-longer-relevant
myproject_WASM_ASYNCIFY_STACK_SIZE cache variable is dropped. A new
CMake-script regression test stubs the target/global option commands,
includes Emscripten.cmake under EMSCRIPTEN=TRUE, and asserts that the
legacy flags are gone, JSPI is emitted, and -fwasm-exceptions remains.

* Address review: remove WASM cmake-script regression test

Requested by @lefticus in PR #156 review.

* Address review: switch WASM EH to -fexceptions, restore Asyncify

Native wasm exceptions (-fwasm-exceptions) are incompatible with legacy
Asyncify, and JSPI is not yet available in all browsers. Switch the
Emscripten exception model to -fexceptions (JS-based) and restore
-sASYNCIFY=1 / -sASYNCIFY_STACK_SIZE so the WASM build keeps working
across every browser that supports threads, until JSPI is universally
available.

Requested by @lefticus in PR #156 review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: leftibot <leftibot@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: leftibot

cmake/Emscripten.cmake

@@ -45,10 +45,13 @@ if(EMSCRIPTEN)
   set(myproject_WASM_ASYNCIFY_STACK_SIZE "65536" CACHE STRING
       "Asyncify stack size in bytes (default: 64KB)")
 
-  # For Emscripten WASM builds, FTXUI requires pthreads and native exception handling
-  # Set these flags early so they propagate to all dependencies
-  add_compile_options(-pthread -fwasm-exceptions)
-  add_link_options(-pthread -fwasm-exceptions)
+  # For Emscripten WASM builds, FTXUI requires pthreads and exception handling.
+  # We use -fexceptions (JS-based exceptions) rather than -fwasm-exceptions
+  # because native wasm exceptions are incompatible with legacy Asyncify, and
+  # JSPI (the modern Asyncify replacement) is not yet shipping in all browsers.
+  # Set these flags early so they propagate to all dependencies.
+  add_compile_options(-pthread -fexceptions)
+  add_link_options(-pthread -fexceptions)
 endif()
 
 # Function to apply WASM settings to a target
@@ -89,7 +92,9 @@ function(myproject_configure_wasm_target target)
       "-sUSE_PTHREADS=1"
       "-sPROXY_TO_PTHREAD=1"
       "-sPTHREAD_POOL_SIZE=${myproject_WASM_PTHREAD_POOL_SIZE}"
-      # Enable asyncify for emscripten_sleep and async operations
+      # Enable Asyncify for emscripten_sleep and other async operations.
+      # Paired with -fexceptions (JS-based exception handling) above, since
+      # Asyncify is not compatible with native wasm exceptions.
       "-sASYNCIFY=1"
       "-sASYNCIFY_STACK_SIZE=${myproject_WASM_ASYNCIFY_STACK_SIZE}"
       # Memory configuration