fix(runtime): expose a C function missing at runtime as undefined instead of asserting

NativeScript/runtime/MetadataBuilder.mm

@@ -117,9 +117,12 @@ NamedPropertyHandlerConfiguration config(MetadataBuilder::GlobalPropertyGetter,
     const FunctionMeta* funcMeta = static_cast<const FunctionMeta*>(meta);
     void* functionPointer =
         SymbolLoader::instance().loadFunctionSymbol(meta->topLevelModule(), meta->name());
+    // Metadata can list functions the running OS or linked binary doesn't export
+    // (newer SDK, weak-linked or stripped symbol); expose those as undefined so
+    // `typeof fn === "undefined"` works as feature detection.
     if (functionPointer == nullptr) {
       Log(@"Unable to load \"%s\" function", meta->name());
-      tns::Assert(false, isolate);
+      return v8::Intercepted::kNo;
     }
 
     CacheItem<FunctionMeta>* item =

TestFixtures/Functions/TNSFunctions.h

@@ -1 +1,5 @@
 CFArrayRef CFArrayCreateWithString(CFStringRef string);
+
+// Declared for the metadata generator but intentionally left undefined, so the
+// symbol is listed in metadata yet absent at runtime.
+void TNSFunctionMissingAtRuntime(void);

TestRunner/app/tests/ApiTests.js

@@ -12,6 +12,13 @@ describe(module.id, function () {
         expect(object.hash).toBe(3);
     });
 
+    it("exposes a C function listed in metadata but missing at runtime as undefined", function () {
+        expect(typeof TNSFunctionMissingAtRuntime).toBe("undefined");
+        expect(global.TNSFunctionMissingAtRuntime).toBeUndefined();
+        expect("TNSFunctionMissingAtRuntime" in global).toBe(false);
+        expect(function () { TNSFunctionMissingAtRuntime(); }).toThrowError(ReferenceError);
+    });
+
     it("preserves a lone high surrogate when bridging a JS string to NSString", function () {
         // A lone high surrogate (U+D834, range U+D800-U+DBFF) is a valid JS string
         // code unit but has no UTF-8 encoding. The old UTF-8 round-trip replaced it