fmt-f2: preserved-tier sweep — lateralProfile <shape>/<crossfall>, road <surface>/<CRG>, <junctionGroup>, <railroad>/<station>, root <include>

[JArmandoAnaya]

Problem

Five spec areas are warned-and-dropped rather than preserved, so a legal file loses them on the first save (one diagnostic, then permanent data loss). All are outside #453's scope list; none needs modeling for v0.1.0 — the preserved-tier (RawXml verbatim) idiom is enough:

Element	Spec	Current behavior
<lateralProfile><shape> (and legacy <crossfall>)	1.9.0 §10.5.1	parse_lateral_profile (core/src/xodr/reader.cpp:732) models <superelevation> only; everything else warn_unsupported → dropped. Round-trip flattens a non-planar carriageway
Road <surface>/<CRG>	§10.6	Not in parse_road's child whitelist (reader.cpp:494) → warned drop; a CRG-referencing file silently loses its surface detail on save
<junctionGroup> (roundabouts)	§12.16	Root sweep (reader.cpp:3219) whitelists header/road/junction/controller/userData → warned drop. Directly relevant to #495 — the standard's own roundabout grouping is currently unrepresentable
<railroad> road child + root <station>	chapter 15	Warned drop, both. A tram file loses its rail layer on save
<include> outside <header>	§7.1	Preserved inside <header> (reader.cpp:392), warned-dropped anywhere else

Expected

Each moves into the preserved tier: read verbatim, written back byte-identically, diagnostic downgraded to the standard "preserved, not modeled" note. Modeling stays with whoever owns the feature later (e.g. #495 for junction groups).

Notes

• Same shape as fmt-f1: remaining non-preserving parse scopes — header (geoReference), roadMark, laneSection, junction children, unknown attributes #453 (fmt-f1); this is the sweep for the scopes fmt-f1: remaining non-preserving parse scopes — header (geoReference), roadMark, laneSection, junction children, unknown attributes #453 did not list.
• Fuzz corpus has no seed for any of these elements — add them with the fix.

Filed by the 2026-07-31 roadmap review.

[JArmandoAnaya]

Fixed by #556 (merged as 15f893a). All five areas reuse #453's capture_unmodeled() — the change is modeled-member lists plus three writer emission points. The diagnostic is downgraded from "is not supported yet and was ignored" (true before, a lie now) to "is preserved verbatim but not modeled; it round-trips unchanged and has no effect in this build". Nothing is modeled; <junctionGroup> modeling stays with #495. Corpus seed preserved_sweep.xodr added.