Pure source rename across objc/objc_block/raylib/sdl3/wasm (~51 sites): fn-decl
markers (bare / 'objc' LIB ref) → 'extern …', and objc.sx's 2 import runtime
classes '#foreign #objc_class("X") {' → '#objc_class("X") extern {'. No bare
defined classes. Behavior-preserving. objc + objc_block validated directly by the
50 marked 13xx corpus examples (incl. import classes 1300/1301 + defined classes
1339/1349); raylib/ffi-sdl3/wasm (no marked importers on host) verified by
byte-identical 'sx ir' probes pre/post. Empty snapshot diff; suite green (647
corpus / 444 unit, 0 failed).
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