Add Customizable JSON Row Preview Fields

JSONViewer/UI/AppShellView.swift

@@ -11,6 +11,7 @@ struct AppShellView: View {
     #endif
     @State private var isInspectorVisible: Bool = false
     @State private var isAISidebarVisible: Bool = false
+    @State private var isPreviewPickerPresented: Bool = false
     @Environment(\.openWindow) private var openWindow
 
     private var displayText: String {
@@ -79,7 +80,10 @@ struct AppShellView: View {
             .navigationSplitViewColumnWidth(min: 420, ideal: 680, max: .infinity)
             .navigationTitle(viewModel.fileURL?.lastPathComponent ?? "Prism")
         }
-
+        .sheet(isPresented: $isPreviewPickerPresented) {
+            PreviewFieldsPickerView(viewModel: viewModel, isPresented: $isPreviewPickerPresented)
+                .frame(minWidth: 520, minHeight: 520)
+        }
         .toolbar {
             ToolbarItemGroup {
                 Button {
@@ -104,6 +108,15 @@ struct AppShellView: View {
                 .frame(width: 100)
                 .help("Toggle between raw text and tree")
 
+                // New: Row preview fields picker
+                Button {
+                    isPreviewPickerPresented = true
+                } label: {
+                    Label("Row Preview", systemImage: "slider.horizontal.3")
+                }
+                .help("Choose which fields are shown in the JSONL sidebar preview")
+                .disabled(viewModel.mode == .none)
+
                 Button {
                     withAnimation {
                         isInspectorVisible.toggle()

JSONViewer/UI/PreviewFieldsPickerView.swift

@@ -0,0 +1,129 @@
+import SwiftUI
+
+struct PreviewFieldsPickerView: View {
+    @ObservedObject var viewModel: AppViewModel
+    @Binding var isPresented: Bool
+
+    @State private var candidates: [String] = []
+    @State private var selected: Set<String> = []
+    @State private var search: String = ""
+    @State private var isLoading: Bool = true
+
+    var body: some View {
+        VStack(alignment: .leading, spacing: 12) {
+            header
+            Divider()
+            content
+            Divider()
+            footer
+        }
+        .padding(16)
+        .onAppear {
+            selected = Set(viewModel.currentSidebarPreviewFields())
+            Task {
+                isLoading = true
+                let paths = await viewModel.collectCandidatePreviewPaths()
+                await MainActor.run {
+                    self.candidates = paths
+                    self.isLoading = false
+                }
+            }
+        }
+    }
+
+    private var header: some View {
+        HStack {
+            Label("Row Preview Fields", systemImage: "slider.horizontal.3")
+                .font(.system(size: 16, weight: .semibold))
+            Spacer()
+            Button {
+                isPresented = false
+            } label: {
+                Image(systemName: "xmark.circle.fill")
+            }
+            .buttonStyle(.plain)
+        }
+    }
+
+    @ViewBuilder
+    private var content: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Text("Choose which JSON fields to show for each JSONL row in the sidebar.")
+                .foregroundStyle(.secondary)
+                .font(.callout)
+
+            HStack(spacing: 8) {
+                Image(systemName: "magnifyingglass")
+                    .foregroundStyle(.secondary)
+                TextField("Filter fields…", text: $search)
+                    .textFieldStyle(.plain)
+            }
+            .padding(.vertical, 8)
+            .padding(.horizontal, 10)
+            .background(RoundedRectangle(cornerRadius: 8).fill(Color(nsColor: .controlBackgroundColor)))
+            .overlay(RoundedRectangle(cornerRadius: 8).strokeBorder(Color.secondary.opacity(0.25), lineWidth: 1))
+
+            if isLoading {
+                VStack(alignment: .center) {
+                    ProgressView().padding(.top, 24)
+                    Text("Scanning document for fields…")
+                        .foregroundStyle(.secondary)
+                        .font(.footnote)
+                }
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+            } else if candidates.isEmpty {
+                Text("No fields found.")
+                    .foregroundStyle(.secondary)
+                    .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .center)
+            } else {
+                let filtered = filteredCandidates
+                List {
+                    ForEach(filtered, id: \.self) { path in
+                        Toggle(isOn: Binding(
+                            get: { selected.contains(path) },
+                            set: { on in
+                                if on { selected.insert(path) } else { selected.remove(path) }
+                            })
+                        ) {
+                            Text(path.isEmpty ? "(root)" : path)
+                                .font(.system(.body, design: .monospaced))
+                        }
+                    }
+                }
+                .frame(minHeight: 320)
+            }
+        }
+    }
+
+    private var footer: some View {
+        HStack {
+            Button {
+                selected.removeAll()
+            } label: {
+                Label("Select None", systemImage: "minus.circle")
+            }
+            Button {
+                selected.formUnion(filteredCandidates)
+            } label: {
+                Label("Select All Shown", systemImage: "checkmark.circle")
+            }
+            Spacer()
+            Button {
+                // Persist and refresh previews
+                let list = candidates.filter { selected.contains($0) }
+                viewModel.setSidebarPreviewFields(list)
+                isPresented = false
+            } label: {
+                Text("Apply")
+            }
+            .keyboardShortcut(.defaultAction)
+            .disabled(isLoading)
+        }
+    }
+
+    private var filteredCandidates: [String] {
+        let q = search.trimmingCharacters(in: .whitespacesAndNewlines)
+        guard !q.isEmpty else { return candidates }
+        return candidates.filter { $0.localizedCaseInsensitiveContains(q) }
+    }
+}

JSONViewer/UI/SidebarView.swift

@@ -84,7 +84,7 @@ struct SidebarView: View {
                                             .lineLimit(2)
                                     }
                                     .id(i)
-                                    .task(id: i) {
+                                    .task(id: "\(i)-\(viewModel.previewFieldsChangeToken)") {
                                         if previews[i] == nil {
                                             viewModel.preview(for: i) { text in
                                                 // Ensure update happens next runloop to avoid update-during-view warnings
@@ -138,10 +138,20 @@ struct SidebarView: View {
                                     Text("Row \(row.id)")
                                         .font(.callout)
                                         .foregroundStyle(.secondary)
-                                    Text(row.preview)
+                                    Text(previews[row.id] ?? "Loading…")
                                         .font(.system(.caption, design: .monospaced))
                                         .lineLimit(2)
                                 }
+                                .id(row.id)
+                                .task(id: "\(row.id)-\(viewModel.previewFieldsChangeToken)") {
+                                    if previews[row.id] == nil {
+                                        viewModel.preview(for: row.id) { text in
+                                            DispatchQueue.main.async {
+                                                previews[row.id] = text
+                                            }
+                                        }
+                                    }
+                                }
                                 .padding(.vertical, 4)
                                 .contentShape(Rectangle())
                                 .onAppear {
@@ -197,5 +207,9 @@ struct SidebarView: View {
         .onChange(of: viewModel.selectedRowID) { _ in
             Task { _ = await viewModel.updateTreeForSelectedRow() }
         }
+        .onChange(of: viewModel.previewFieldsChangeToken) { _ in
+            // Clear local previews so visible rows re-fetch with new field selection
+            previews = [:]
+        }
     }
 }