Learnings

HKStateOfMind write APIs are directly available on iOS 18+ and can be created with date/kind/valence/labels/associations in one call.
Moodwell exports can include large arrays and sparse optional fields, so dry-run validation is necessary before committing to HealthKit.
Headless/sandboxed xcodebuild may fail SwiftUI #Preview macro expansion, so keeping previews out of CI-oriented builds avoids false negatives.
In .strings files, %@ with integer arguments in String(format:) can trigger EXC_BAD_ACCESS; use numeric specifiers like %ld and String.localizedStringWithFormat.