SampleTrips Previews work, but not in my primary project.

I wanted to get my SwiftData previews working in my primary project, so I started modeling them after the SampleTrips project.

After messing around with that & being unable to make it work, I brought the same (working) sample code into my main project, unfortunately that's not working...

I've attached the preview error (note, there's nothing in the Diagnostic Reports).

//Sample code that works in it's own project, but not my primary target.

import SwiftUI
import SwiftData

struct TestSwiftDataStuffView: View {
    let trip: Trip
    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundStyle(.tint)
            Text("Hello, \(trip.name)!")
                .padding()
                .foregroundColor(.red)
        }
        .padding()
    }
}

#Preview(traits: .sampleDataSecondary) {
    @Previewable @Query var trips: [Trip]
    TestSwiftDataStuffView(trip: trips.first!)
}

actor DataModelSecondary {
    struct TransactionAuthor {
        static let widget = "widget"
    }
    
    static let shared = DataModelSecondary()
    private init() {}
    
    nonisolated lazy var modelContainer: ModelContainer = {
        let modelContainer: ModelContainer
        
        let schema = Schema([
            Trip.self
        ])
        
        do {
            let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false, cloudKitDatabase: .none)
            modelContainer = try ModelContainer(for: schema, configurations: [modelConfiguration])
        } catch {
            fatalError("Failed to create the model container: \(error)")
        }
        return modelContainer
    }()
}
@Model class Trip {
    
    @Attribute(.preserveValueOnDeletion)
    var name: String
    
    init(name: String) {
        self.name = name
    }
}

extension Trip {
    static var previewTrips: [Trip] {
        [
            Trip(name: "Revenant"),
            Trip(name: "Newcastle"),
            Trip(name: "Bianca")
        ]
    }
}

struct SampleDataSecondary: PreviewModifier {
    static func makeSharedContext() throws -> ModelContainer {
        let config = ModelConfiguration(isStoredInMemoryOnly: true)
        let container = try ModelContainer(
            for: Trip.self,
            configurations: config
        )
        SampleDataSecondary.createSampleData(into: container.mainContext)
        return container
    }
    
    func body(content: Content, context: ModelContainer) -> some View {
        content.modelContainer(context)
    }
    
    static func createSampleData(into modelContext: ModelContext) {
        Task { @MainActor in
            let sampleDataTrips: [Trip] = Trip.previewTrips
            let sampleData: [any PersistentModel] = sampleDataTrips //+ sampleDataLA + sampleDataBLT
            sampleData.forEach {
                modelContext.insert($0)
            }
            
            try? modelContext.save()
        }
    }
}

@available(iOS 18.0, *)
extension PreviewTrait where T == Preview.ViewTraits {
    @MainActor static var sampleDataSecondary: Self = .modifier(SampleDataSecondary())
}