feat(proj): init

mobile/lib/core/state/async_value.dart

@@ -0,0 +1,41 @@
+/// Minimal async state container so screens can pattern-match over
+/// loading / data / error instead of juggling three nullable fields.
+sealed class AsyncValue<T> {
+  const AsyncValue();
+
+  const factory AsyncValue.loading() = AsyncLoading<T>;
+  const factory AsyncValue.data(T value) = AsyncData<T>;
+  const factory AsyncValue.error(String message) = AsyncError<T>;
+
+  T? get valueOrNull => this is AsyncData<T> ? (this as AsyncData<T>).value : null;
+
+  bool get isLoading => this is AsyncLoading<T>;
+
+  R map<R>({
+    required R Function() loading,
+    required R Function(T value) data,
+    required R Function(String message) error,
+  }) {
+    return switch (this) {
+      AsyncLoading<T>() => loading(),
+      AsyncData<T>(value: final v) => data(v),
+      AsyncError<T>(message: final m) => error(m),
+    };
+  }
+}
+
+final class AsyncLoading<T> extends AsyncValue<T> {
+  const AsyncLoading();
+}
+
+final class AsyncData<T> extends AsyncValue<T> {
+  const AsyncData(this.value);
+
+  final T value;
+}
+
+final class AsyncError<T> extends AsyncValue<T> {
+  const AsyncError(this.message);
+
+  final String message;
+}