12 commits this session shipped the entire M4 milestone. sx-defined
Obj-C classes now honor `context.allocator` end-to-end, route through
NSObject's retain/release at the source-language level, and emit
correct ARC ops in property setters/getters/dealloc per the Apple
ABI contract.
189/189 example tests pass; chess on iOS-sim green throughout.
Ready for M5 (closure↔block bridge) or M1.1.b (Class(T) phantom
typing) next session.
e5ba06b66c