ffi 3.2 C4: migrate uikit.sx UIKit chrome cluster to #objc_class

Fourth cluster — was blocked on issue-0043, now unblocked by the
preceding `Self`-substitution fix.

Classes declared:

- UIScreen         → mainScreen (class), nativeScale + bounds (instance)
- UIView           → safeAreaInsets, addSubview, layer (all instance)
- UIWindow         → alloc (class), initWithWindowScene, setRootViewController,
                     makeKeyAndVisible, screen (instance)
- UIViewController → alloc (class), init, setView (instance)
- UITextField      → alloc (class), init, becomeFirstResponder,
                     resignFirstResponder (instance)

Migration sites in uikit.sx:

- `show_keyboard` / `hide_keyboard` → `tf.becomeFirstResponder()` /
  `tf.resignFirstResponder()` on a `*UITextField` cast of `text_field`.
- `uikit_refresh_safe_insets` → `gl_view.safeAreaInsets()` on a
  `*UIView` cast of `plat.gl_view`.
- `uikit_read_screen_scale` and GL-context bring-up →
  `UIScreen.mainScreen().nativeScale()`.
- `uikit_keyboard_will_change_frame` → `win.screen().bounds()`.
- `uikit_scene_will_connect_ios` (the function that triggered 0043) →
  `UIWindow.alloc().initWithWindowScene(scene)`,
  `UIViewController.alloc().init()`, `vc.setView(...)`,
  `win.setRootViewController(...)`, `gl_view.layer()`,
  `UITextField.alloc().init()`, `gl_view.addSubview(...)`,
  `win.makeKeyAndVisible()`.

Three `objc_getClass(...)` lookups (UIWindow, UIViewController,
UITextField) are gone — the class slots come from the declarative
bindings via `__sx_objc_class_init`. UIScreen has the same shape.

167/167 example tests; chess clean on macOS / iOS sim / Android via
`tools/verify-step.sh`.

current/CHECKPOINT-FFI.md

@@ -568,32 +568,59 @@ blocks. The `link` parameter on the `sxTick:` callback is now cast
 to `*CADisplayLink` at function entry so subsequent method calls
 type-check.
 
-**Phase 3.2 C4/C5 BLOCKED on issue-0043.** Attempted C4 migration
-(UIKit chrome: UIScreen / UIWindow / UIViewController / UITextField
-/ UIView) surfaced a real compiler bug: lazy-lowered function bodies
-don't resolve foreign-class method dispatch when invoked transitively
-from an `inline if OS == .ios` branch in another function. The
-specific failure is in `uikit_scene_will_connect_ios` whose body
-contains `UIWindow.alloc().initWithWindowScene(scene)` and
-`win.setRootViewController(...)` — both work in isolated probes but
-fail at compile time when the function is reached via lazy lowering
-from chess's iOS scene-connect hook. macOS target builds fine; only
-ios-sim trips it. C1/C2/C3 happened to land cleanly because the
-methods they migrate are reached eagerly (or are niladic so the
-dispatch path doesn't hit the failing branch).
+**issue-0043 closed.** The "lazy-lower" framing in the issue file
+turned out to be a red herring: the actual root cause was that
+`inferExprType` for a chained call `Cls.static().instance(...)` never
+looked the inner call's foreign-class declaration up, so the outer
+dispatch saw a `.s64` receiver, the `foreign_class_map.get(...)` lookup
+missed, and lowering emitted `error: unresolved 'method'`. The macOS
+target appeared to work because `inline if OS == .ios { ... }` strips
+the gated body before lowering — eliding every call that would have
+exercised the broken path.
 
-The C4 work is reverted to keep the tree green at C3. C4+C5 stay
-pending until issue-0043 is fixed in a separate session.
+Fix in `src/ir/lower.zig`:
+1. `inferExprType` for `.call` with `.field_access` callee now checks
+   `foreign_class_map` for both shapes — `Cls.static_method(args)` (object
+   identifier matches a foreign-class alias, look up static members) and
+   `inst.instance_method(args)` (receiver is a pointer to a foreign-class
+   struct, look up non-static members).
+2. New helpers `resolveForeignMethodReturnType` /
+   `resolveForeignClassMemberType` substitute `*Self` / `Self` to the
+   foreign-class struct so a `*Self` return doesn't synthesize a phantom
+   `Self`-named struct that future dispatches can't resolve.
+3. The Obj-C lowering paths (`lowerObjcMethodCall`, `lowerObjcStaticCall`)
+   route through the same helper for `ret_ty` so the IR Ref's type matches
+   what `inferExprType` reports.
+
+`examples/138-foreign-class-chained-dispatch.sx` locks in the regression
+via two shapes against NSObject's `+alloc` / `-init` chain: `*NSObject`
+return then `*Self` return, and `*Self` then `*Self`. Runs on the host
+(macOS) for live exercise; non-macOS hosts fall through to a stub
+matching the expected output.
+
+Phase 3.2 C4 landed: UIKit chrome cluster migrated. Six classes
+declared (UIScreen, UIView, UIWindow, UIViewController, UITextField
+— plus the existing C1/C2/C3 classes already in place). Migration
+sites: `show_keyboard` / `hide_keyboard` use `tf.becomeFirstResponder()`
+/ `tf.resignFirstResponder()`; `uikit_refresh_safe_insets` uses
+`gl_view.safeAreaInsets()`; `uikit_read_screen_scale` and the GL-
+context bring-up both use `UIScreen.mainScreen().nativeScale()`;
+keyboard-frame callback uses `win.screen().bounds()`; the scene-
+connect bring-up chains `UIWindow.alloc().initWithWindowScene(scene)`
+and `UIViewController.alloc().init()` then `vc.setView(...)`,
+`win.setRootViewController(...)`, `gl_view.layer()`,
+`UITextField.alloc().init()`, `gl_view.addSubview(...)`,
+`win.makeKeyAndVisible()`. Three `objc_getClass(...)` calls (UIWindow,
+UIViewController, UITextField) are gone — the class slots come from
+the declarative bindings via `__sx_objc_class_init`. C4 is the
+cluster that triggered issue-0043; with the fix in, the chained
+dispatch resolves correctly under lazy lowering. 167/167 tests +
+chess clean on macOS / iOS sim / Android.
 
 Open work:
-- **issue-0043** — investigate + fix the lazy-lower foreign-class
-  dispatch bug. See `issues/0043-lazy-lower-loses-foreign-class-method-dispatch.md`
-  for the reproduction and investigation prompt.
-- **Phase 3 step 3.2 — C4..C5** — uikit.sx migration, blocked until
-  0043 lands.
-  test for the default-mangling table. Escape hatch for selectors
-  that don't fit the underscore-split rule (e.g. `tableView_
-  numberOfRowsInSection_` with an asymmetric keyword count).
+- **Phase 3 step 3.2 — C5** — uikit.sx migration (view tree + GL
+  drawables: CAEAGLLayer, EAGLContext, plus any remaining
+  CAMetalLayer / NSTimer sites).
 - **Phase 3 step 3.3** — `property name: Type` synthesizes
   `inst.name` → `[inst name]` getter and `inst.name = x` →
   `[inst setName: x]` setter. `#setter("...")` overrides the setter
@@ -989,6 +1016,27 @@ zig build && zig build test && bash tests/run_examples.sh && bash tests/cross_co
   `Gles3Gpu`. Instrumentation stripped after fix. 140 host + 9
   cross tests green.
 
+- 2026-05-25: issue-0043 closed — chained `Cls.static().instance(...)`
+  foreign-class dispatch. `inferExprType` for `.call` with `.field_access`
+  callee now consults `foreign_class_map` for both static (object is the
+  alias) and instance (receiver type is `*ForeignClass`) shapes. New
+  `resolveForeignMethodReturnType` / `resolveForeignClassMemberType` /
+  `foreignClassStructType` helpers substitute `*Self` / `Self` to the
+  foreign class's own struct so the chained receiver type doesn't
+  collapse to a phantom `Self`-named struct. `lowerObjcMethodCall` /
+  `lowerObjcStaticCall` route through the same helper so the IR Ref's
+  recorded ret_ty matches what `inferExprType` reports. Pre-fix:
+  `UIWindow.alloc().initWithWindowScene(scene)` (and any other chained
+  shape) collapsed the inner ret to `.s64`, the next dispatch's
+  `foreign_class_map.get(...)` missed, and lowering emitted
+  `error: unresolved 'initWithWindowScene'`. The "lazy-lower" wording in
+  the issue file is a red herring — the bug fires on direct calls too;
+  macOS chess hides it only because `inline if OS == .ios { ... }`
+  strips the gated bodies that exercise the chain. Locked in by
+  `examples/138-foreign-class-chained-dispatch.sx` (NSObject `+alloc` /
+  `-init` chain in both `*Cls` and `*Self` return-type shapes). 167
+  host + 7 cross tests green. Phase 3.2 C4/C5 is unblocked.
+
 ## Known issues
 
 - `signed char` C maps to sx `u8` in c_import.zig (current behavior;