ENGLISH·COURSE API
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    GetPlaybackPosition: (
        input: { lessonId: LessonId },
    ) => ResultAsync<{ seconds: number | null }, GetPlaybackPositionErrors>

    Use case: read the persisted playback position for a lesson.

    Resolves to { seconds: number | null } — null when the adapter has no entry for the lesson. The use case never throws.

    Type Declaration