Problem

VehicleDetails.tsx currently hydrates its edit form from VehicleGQLShaped — the projection row used by the list — via hydrateFromRow() (src/data/vehicles/vehicleFormDefaults.ts). That row only carries the few columns the list needs (registrationNumber, operationalNumber, transportType.{id,name,transportMode}, version). It is missing the bulk of the NeTEx Vehicle shape — Name, Description, ShortName, BuildDate, ChassisNumber, RegistrationDate, keyList, ValidBetween, VehicleModelRef, etc. — so the form can never round-trip a real Vehicle.

The Sobek single-vehicle export endpoint is in place:

• GET /services/vehicles/netex/vehicles/{id} → PublicationDelivery XML (CompositeFrame → ResourceFrame → vehicles → <Vehicle>), with Accept: application/xml. Unknown id returns an empty ResourceFrame.

This issue switches details hydration to that endpoint. Save path already round-trips via useVehiclePairSave → buildVehiclePairXml → import — this aligns the read side with it.

Scope (Hathor only)

1. Add fetchVehicleNetexXml(applicationImportBaseUrl, id, token) under src/data/vehicles/xml/ — GET ${base}/vehicles/${encodeURIComponent(id)}, Accept: application/xml, returns raw string.
2. Add parseVehicleXml(xml): Partial<Vehicle> — uses fast-xml-parser's XMLParser (already a dep, see src/data/vehicle-imports/xmlUtils.ts:106) to drill PublicationDelivery → dataObjects → (CompositeFrame.frames?.ResourceFrame ?? ResourceFrame) → vehicles → Vehicle[0]. Reuse findResourceFrame + toArray from xmlUtils.ts. Map the parsed shape into the Vehicle interface declared in src/data/vehicles/xml/Vehicle.ts.
3. Add useVehicle(id) hook — mirrors useVehicles() lifecycle (fetch on id/baseUrl change, loading/error/refetch), returns { data: Partial<Vehicle> | null, loading, error, refetch }.
4. VehicleDetails.tsx: replace the hydrateFromRow(vehicle) path with the new hook. Keep the GQL row only for the header context strip (transport-type chip + mode chip) until issue Vehicle + VehicleModel combined details form (phase 2) #69 reshapes that too. The edit form (VehicleEditForm) gets fed the XML-shaped data directly.
5. Delete vehicleFormDefaults.ts:hydrateFromRow once nothing else references it. BLANK_FORM stays — "New Vehicle" flow still needs it.

Open design question (handled in PR)

fast-xml-parser's default shape does not match xml/Vehicle.ts:

Two acceptable approaches:

• (a) Parser adapter — keep xml/Vehicle.ts as the truth; write a thin xmlToVehicle() that renames keys (@_ → \$), unwraps { '@_ref' } to string, and forces arrays via XMLParser's isArray callback on the known list fields. This is the inverse of the existing vehicleToXmlShape() write mapper.
• (b) Adopt the parser shape — change xml/Vehicle.ts (and VehicleEditForm's readers like firstText) to consume @_ / #text / { '@_ref' } directly, then update Vehicle-mapping.ts to be identity-shaped on the parsed half. Bigger blast radius but eliminates two transforms.

Decision happens during PR: build a small fixture from the export-seed (vehicle-export-seed.xml in Sobek), parse with XMLParser, diff against Vehicle interface, then pick. If the gap turns out to be wide enough that neither option is clean, retrofit Vehicle.ts / EditForm to the XML shape per the user's plan ("the details form will be retrofitted to align with the xml shaped vehicle").

Out of scope

• Restructuring VehicleDetails.tsx away from its sidebar form (issue Vehicle + VehicleModel combined details form (phase 2) #69 — phase-2 combined vehicle+model form).
• Removing the GQL vehicle(id:) fetch on the list-row click path — list still needs the projection row for sort/filter; the row also seeds the header strip until Vehicle + VehicleModel combined details form (phase 2) #69 lands.
• Changes to VehicleEditForm's field set — that follows once the parsed shape is wired in and we can see what populates vs. what's empty.

Verification

• npm run local against Sobek :37999. Click a vehicle in the list → details slider opens → form fields populated from the NeTEx fetch (not just registration number + op number). Edit a field → save → re-open → field persists.
• Network tab shows the GET /netex/vehicles/{id} round-trip.
• Unknown-id route still renders the existing "Vehicle not found" empty state (empty vehicles array from the parser).