Build with VerSky.

def resolve_via_dfr(a: NegotiateInit, b: NegotiateInit) -> str:
    """Both vehicles compute the same resolution.
    Returns vehicle_id of the YIELDING vehicle.

    Hierarchy:
      1. Mission priority class
      2. Remaining energy level
      3. Current heading value
      4. Vehicle identifier (lexicographic)
    """
    rank_a = PRIORITY_RANK[a.mission_priority]
    rank_b = PRIORITY_RANK[b.mission_priority]
    if rank_a != rank_b:
        return b.vehicle_id if rank_a < rank_b else a.vehicle_id

    if a.energy_remaining_pct != b.energy_remaining_pct:
        return (a.vehicle_id
                if a.energy_remaining_pct > b.energy_remaining_pct
                else b.vehicle_id)

    if a.current_heading_deg != b.current_heading_deg:
        return (a.vehicle_id
                if a.current_heading_deg < b.current_heading_deg
                else b.vehicle_id)

    if a.vehicle_id != b.vehicle_id:
        return a.vehicle_id if a.vehicle_id < b.vehicle_id else b.vehicle_id

    return a.vehicle_id  # degenerate case — same identity