Jetpack DataStore for Android and KMP

Reactive coroutine-based key-value / typed storage; the same androidx.datastore:datastore-preferences-core runs on Android, iOS, and JVM — only the file-path producer is platform-specific. (Web support is 1.3.0-alpha only, and it's sessionStorage/OPFS-backed there, not file-path-based.) This reference covers the storage-choice call plus the two error/path traps, not the basics of Preferences keys, edit { }, or Serializer<T>. Adapted from Meet-Miyani/compose-skill; MIT. Related: android-skills:android-data-layer, android-skills:kmp-boundaries, android-skills:kotlin-flows.

Preferences vs Typed vs Room

Need	Storage
Key-value flags (theme, locale, onboarding done)	Preferences DataStore
One typed object, many related fields, schema evolution	Typed DataStore + `Serializer<T>`
Relational data, indexes, `WHERE` / `JOIN`, >100 entries, paging	Room
Payloads above ~50KB per write	Room / filesystem — DataStore rewrites the whole file on every `edit`

Rule of thumb: if a WHERE clause would be useful, use Room.

The two traps

.catch must match IOException specifically — never a broad catch. A bare catch { emit(emptyPreferences()) } swallows CancellationException (breaking structured concurrency) and hides serializer/corruption errors behind a silent empty state.