타깃 하나, 기기 둘, 배치는 크기 클래스로

targets:
  SparkMobile:
    type: application
    platform: iOS
    deploymentTarget: "17.0"
    settings:
      base:
        PRODUCT_BUNDLE_IDENTIFIER: com.example.spark.mobile
        TARGETED_DEVICE_FAMILY: "1,2"     # 1 = iPhone, 2 = iPad: one target, one binary, one record

import SwiftUI

struct Note: Identifiable, Hashable, Sendable {
    let id: String          // the client-minted id: stable before AND after the engine knows it
    var title: String
    var isOnEngine: Bool
}

@MainActor
@Observable
final class Library {
    var serverNotes: [Note] = []     // fetched from the engine
    var localNotes: [Note] = []      // written here, not yet listed by the engine

    /// One list for the sidebar. A note moves from local to server by id; it never leaves.
    var rows: [Note] {
        let known = Set(serverNotes.map(\.id))
        return localNotes.filter { !known.contains($0.id) } + serverNotes
    }

    func note(_ id: String?) -> Note? { rows.first { $0.id == id } }
}

struct LibraryView: View {
    @State private var library = Library()
    @State private var selection: String?
    @Environment(\.horizontalSizeClass) private var sizeClass

    var body: some View {
        // Columns on a regular-width iPad, a stack on iPhone and in a narrow iPad split.
        NavigationSplitView {
            List(library.rows, selection: $selection) { note in
                Text(note.title).tag(note.id)
            }
            .navigationTitle("Notes")
        } detail: {
            if let note = library.note(selection) {
                Text(note.title).navigationTitle(note.title)
            } else {
                ContentUnavailableView("No Note Selected", systemImage: "doc.text")
            }
        }
        .onChange(of: library.rows) {
            // The class of bug: in compact width, a selected row that vanishes can pop the detail.
            if let selection, library.note(selection) == nil {
                print("selection \(selection) is not in the sidebar rows (size class: \(String(describing: sizeClass)))")
            }
        }
    }
}