Function apply_command 

pub fn apply_command(
    plan: &mut Plan,
    actor: ActorId,
    command: Command,
    timestamp: DateTime<Utc>,
    id: OperationId,
) -> Result<Operation, EngineError>

Apply one validated semantic command atomically and return its audit operation.

Errors leave every field, including the revision, unchanged. Revisions wrap at u64::MAX. The caller supplies the operation identity so replaying a recorded operation reproduces it exactly; the engine itself holds no source of randomness.