Function dsf_observation_beyond_90pct 

pub fn dsf_observation_beyond_90pct(
    range_m: f64,
    solved_max_range_m: f64,
) -> bool

Whether an observation range is beyond 90% of the trajectory’s solved max range — past this point the solution’s reliability degrades (short-range extrapolation of a trajectory that terminated, e.g., at ground impact just past the observation).

Moved out of main.rs alongside dsf_observation_warrants_90pct_warning (MBA-1357 Task 8): it isn’t one of that task’s four named helpers, but dsf_observation_warrants_90pct_warning calls it, and a library function cannot call a private binary-crate function, so it had to move too. Verbatim, unchanged.