Four root causes for "chess UI shows white screen" — all fixed:
1. Hybrid legacy-app + scene-API path on iOS 26. Without
UIApplicationSceneManifest in the Info.plist, iOS 26 booted us in
[rb-legacy] mode and -[UIApplication connectedScenes] returned an
empty set. didFinishLaunching's window-setup code bailed at "no scene"
and the UIWindow never appeared on screen. Fix: emit the manifest in
buildInfoPlist (src/target.zig) AND split the window/view/layer setup
from didFinishLaunching into a new SxSceneDelegate's
scene:willConnectToSession:options: IMP. didFinishLaunching now just
subscribes the keyboard observer and returns YES.
2. UISceneDelegate formal protocol conformance. iOS 26 checks
-[cls conformsToProtocol:@protocol(UISceneDelegate)] before
instantiating the scene delegate; without it the runtime logs
"SxSceneDelegate does not conform to the UISceneDelegate protocol"
and silently uses a default delegate that does nothing. Fix:
look up UISceneDelegate + UIWindowSceneDelegate via objc_getProtocol
and class_addProtocol BEFORE objc_registerClassPair. The protocol
metadata is present at link time (unlike UIApplicationDelegate per
the long-standing legacy note in CHECKPOINT).
3. Protocol method return types via type aliases lowered as void.
The GPU protocol declares `create_shader(...) -> ShaderHandle` where
`ShaderHandle :: u32`. The protocol-decl lowering at lower.zig:7547
passed the return AST node through type_bridge.resolveAstType which
doesn't know about the type_alias_map. resolveTypeName fell through
to its "assume named struct" branch and registered ShaderHandle as
an empty struct ({ }). LLVM IR for the protocol call_indirect then
read `call {} %fn_ptr(...)` — return value discarded; the
subsequent abi.coerce load from a zero-init'd alloca yielded 0.
Symptom: UIRenderer.mtl_shader = 0, set_shader sees state == null,
the render-encoder fires draw with no pipeline state bound, GPU
rejects the command buffer with MTLCommandBufferErrorInternal.
Fix: at the protocol-decl method-type resolution sites in
lower.zig, check type_alias_map BEFORE falling through to
type_bridge.resolveAstType for both params and return type. A
chess-side companion fix in /Users/agra/projects/game/main.sx
(separate commit) memsets the MetalGPU struct after alloc so the
List(*void) fields' len/cap/items aren't garbage.
After all four (this commit + memset companion in chess repo):
- 71/71 regression tests pass.
- Chess game now boots, scene-connects, ticks CADisplayLink, renders
dark-gray clear + UI text + panel dividers every frame on iOS sim.
- Metal-clear example still renders.
Chess board + pieces visual contrast and faint-text-color are remaining
visual-polish items, not compiler/platform-setup issues.
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