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Andrew Heard
acbf36caee
GeminiAPIClient's SessionDelegate and TaskDelegate stored Synchronization.Mutex properties. Swift classes are listed in the Objective-C class list regardless of @available, so enumerating the classes (e.g., with objc_copyClassList, as Realm does) or looking one up by name realized them on iOS 17 and earlier. TaskDelegate's Mutex<ResponseState> required runtime layout, so realizing it called the weakly linked Mutex metadata accessor, which is NULL before iOS 18, and the app crashed. GeminiLanguageModel is only built with Swift 6.4+, so this affected apps built with Xcode 27 even if they didn't use it. - Replace Mutex with LockedValue, an NSLock-based class that mirrors the init and withLock signatures of Mutex. Add a TODO to switch back once the minimum deployment targets always include Mutex, and link the upstream Swift runtime issues (swiftlang/swift#61215 and swiftlang/swift#72657). - Add a FirebaseAILogicUnit test that calls objc_copyClassList. No CI runner has a simulator old enough to catch this crash, so the fix was verified locally on a tvOS 17.5 simulator, before and after. Fixes #17012