Verify-step uncovered three categories of regressions where sx code
calls into the platform's C ABI through fn-pointer types or as a
registered callback. Every site now declares the right convention.
C-side calls INTO sx → callconv(.c) on the sx function:
- platform/android.sx: sx_android_render_thread_entry is the start
routine pthread_create invokes — pthread treats it as a C function.
Also annotate the pthread_create signature so the start-routine fn-
pointer field rejects mismatching sx fns at compile time.
sx code calling typed fn-pointers cast from C symbols → callconv(.c)
on the fn-pointer type:
- opengl.sx: 55 GL fn-ptr globals + load_gl's proc-loader param. GL
trampolines are macOS/iOS/Android system code.
- std/objc.sx: the two typed `objc_msgSend` casts.
- gpu/metal.sx: ~40 typed `objc_msgSend` casts across Metal command
encoder / device / pipeline construction.
The block invoke trampolines (objc_block.sx) call back INTO sx (the
closure trampoline). The typed fn-ptr there stays default-conv so
ctx prepends correctly. Compiler change: a callconv(.c) sx function
now binds `current_ctx_ref` to `&__sx_default_context` at entry (used
to be gated by `isExportedEntryName`). C-callable sx callbacks like
the block invokes don't get their own __sx_ctx param but their bodies
still need a real Context to forward to the closure they delegate to.
Tests: 152/152 example suite + chess green on all 3 platforms.
Screenshots at /tmp/sx-game-{macos,iossim,android}.png.
