Function derive_dsf_point_v1 

pub fn derive_dsf_point_v1(
    req: &DsfDeriveRequestV1,
) -> Result<DsfPointResultV1, DsfServiceErrorV1>

Derive a dsf point from a bare scalar-BC model (MBA-1357 Task 9) — the JSON bridge’s entry point, with no saved profile behind it.

Builds DsfSolveInputs from req.model via the existing From impl (bridge defaults: no wind, level shot, no zero-POI/sight-mount offsets, ICAO BC reference, no BC segments, no custom drag curve — see that impl’s own doc comment), sizes a solve envelope the same way the CLI’s own default does, solves, and hands the result to derive_dsf_point_from_solve_v1 for the actual derivation.

Derive only — never writes a DSF table, opens a profile, touches the filesystem, or calls std::process::exit.