iPad: adaptive sidebar+detail shell and Mac-style diff (remote Phases 1-2)

Grow the universal NucleicRemote app into a width-adaptive shell so a
regular-width iPad renders the macOS sidebar+detail IA while the iPhone
keeps its TabView -- both over the same RemoteStore projection (one host
authority, N renderers).

Phase 1 (adaptive shell):
- AdaptiveRootView branches on horizontalSizeClass: CompactRootView (the
  existing iPhone TabView, moved verbatim) vs SplitRootView
  (NavigationSplitView) on regular width.
- SplitSidebar: Home/Projects/To-dos/Settings destinations + sessions
  grouped under their projects (attention-sorted), connection chip footer.
- SplitDetail selects a destination or a session; a selected session reuses
  SessionDetailView keyed .id(sessionID) so switching drives open/close.
- RemoteStore.closeOpen(_:) is now id-guarded so a split-view A->B switch
  (onAppear(B) before onDisappear(A)) can't tear down B's fresh subscription.
- IdentityStore.deviceID idiom-tags the prefix (ipad-/iphone-) for new
  installs so the host lists a paired iPad correctly.

Phase 2 (width tuning + diff):
- readableColumn() caps+centers Home and the transcript on wide layouts;
  a no-op at phone/portrait width.
- SessionDiffView switches on available width (GeometryReader): a Mac-style
  two-pane diff (file list + selected file's patch) on wide/landscape, the
  phone stack otherwise. UnifiedPatch splits the combined patch per file.
  Read-only, same wire, no protocol change.
- Demo diff fixture now carries both files' patches.

iPhone layout and behavior unchanged. Builds clean; verified in the iPad
simulator (demo mode).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

NucleicRemote/NucleicRemote/Models/IdentityStore.swift

@@ -1,6 +1,9 @@
 import Foundation
 import Security
 import NucleicProtocol
+#if canImport(UIKit)
+import UIKit
+#endif
 
 /// What the phone pins about its Mac at pairing (SYNC §4.2): the host's static key (for IK
 /// reconnect), a display name, and the transport + connection hint from the QR — LAN
@@ -42,11 +45,22 @@ enum IdentityStore {
     static func deviceID() -> String {
         let defaults = UserDefaults.standard
         if let existing = defaults.string(forKey: deviceIDKey) { return existing }
-        let id = "iphone-" + UUID().uuidString.prefix(8).lowercased()
+        let id = deviceIDPrefix + UUID().uuidString.prefix(8).lowercased()
         defaults.set(id, forKey: deviceIDKey)
         return id
     }
 
+    /// Idiom-tagged prefix so the host lists a paired device with the right kind/icon
+    /// (`ipad-…` vs `iphone-…`). Only stamps *freshly generated* ids — an existing install
+    /// keeps whatever id it already persisted, so upgrading a phone never changes its identity.
+    private static var deviceIDPrefix: String {
+        #if canImport(UIKit)
+        return UIDevice.current.userInterfaceIdiom == .pad ? "ipad-" : "iphone-"
+        #else
+        return "iphone-"
+        #endif
+    }
+
     static func loadPairedHost() -> PairedHost? {
         guard let data = UserDefaults.standard.data(forKey: pairedHostKey) else { return nil }
         return try? JSONDecoder().decode(PairedHost.self, from: data)

NucleicRemote/NucleicRemote/Models/RemoteStore.swift

@@ -290,6 +290,17 @@ final class RemoteStore: ObservableObject {
             +  if (!token) throw new AuthError("missing bearer token")
                return verify(token)
              }
+            diff --git a/auth/session.ts b/auth/session.ts
+            new file mode 100644
+            --- /dev/null
+            +++ b/auth/session.ts
+            @@ -0,0 +1,6 @@
+            +export interface Session {
+            +  userId: string
+            +  issuedAt: number
+            +}
+            +
+            +export const SESSION_TTL = 3600
             """)
     }
 
@@ -648,11 +659,17 @@ final class RemoteStore: ObservableObject {
         ApprovalID(rawValue: "demo-appr-\(sessionID.rawValue)")
     }
 
-    func closeOpen() {
-        if let id = openSessionID {
-            send(.unsubscribe(id))
-            markOpened(id)  // everything up to now has been seen
-        }
+    /// Close a session's live subscription. `id` names *which* session is closing — the detail
+    /// view passes its own. On iPad's split view, switching session A→B can mount B (which calls
+    /// `open(B)`, setting `openSessionID = B`) *before* A's detail disappears; so we always
+    /// unsubscribe the named session but only tear down the shared open-state when it still
+    /// belongs to that session — otherwise we'd wipe B's freshly-loaded transcript. Called with
+    /// no argument it closes whatever is currently open (the iPhone push/pop path, unchanged).
+    func closeOpen(_ id: SessionID? = nil) {
+        guard let target = id ?? openSessionID else { return }
+        send(.unsubscribe(target))
+        markOpened(target)  // everything up to now has been seen
+        guard openSessionID == target else { return }
         openSessionID = nil
         openEvents = []
         openApprovals = []

NucleicRemote/NucleicRemote/NucleicRemoteApp.swift

@@ -36,8 +36,6 @@ struct NucleicRemoteApp: App {
 
 struct RootView: View {
     @EnvironmentObject var store: RemoteStore
-    // Initial tab; overridable via NUCLEIC_TAB for offline UI previews.
-    @State private var tab = Int(ProcessInfo.processInfo.environment["NUCLEIC_TAB"] ?? "") ?? 0
     // Appearance preferences — same storage keys and semantics as the Mac's Settings →
     // Appearance, so both devices honor the same choices.
     @AppStorage(AppAppearance.storageKey) private var appearanceRaw = AppAppearance.system.rawValue
@@ -52,30 +50,15 @@ struct RootView: View {
             DemoBanner()
             Group {
                 if store.isPaired {
-                    TabView(selection: $tab) {
-                        HomeView()
-                            .tabItem { Label("Home", systemImage: "house") }.tag(0)
-                        SessionsView()
-                            .tabItem { Label("Sessions", systemImage: "square.stack.3d.up") }
-                            .badge(store.needsYouCount).tag(1)
-                        ProjectsView()
-                            .tabItem { Label("Projects", systemImage: "folder") }.tag(2)
-                        TodosView()
-                            .tabItem { Label("To-dos", systemImage: "checklist") }.tag(3)
-                        SettingsView()
-                            .tabItem { Label("Settings", systemImage: "gearshape") }.tag(4)
-                    }
+                    // Width-adaptive shell: the iPhone's TabView on compact width, the Mac's
+                    // sidebar+detail split on a regular-width iPad (see AdaptiveRootView).
+                    AdaptiveRootView()
                 } else {
                     PairingIntroView()
                 }
             }
         }
         .overlay(alignment: .bottom) { ErrorBubble() }
-        // A notification tap routes to its session: jump to the Sessions tab, where
-        // `SessionsView` consumes `pendingRoute` and pushes the detail.
-        .onChange(of: store.pendingRoute) { _, route in
-            if route != nil { tab = 1 }
-        }
         .tint(Palette.accent)
         .preferredColorScheme((AppAppearance(rawValue: appearanceRaw) ?? .system).colorScheme)
         .dynamicTypeSize((AppTextSize(rawValue: textSizeRaw) ?? .medium).dynamicTypeSize)

NucleicRemote/NucleicRemote/Views/AdaptiveRootView.swift

@@ -0,0 +1,213 @@
+import SwiftUI
+import NucleicProtocol
+
+/// Chooses the navigation shell by width so one universal binary serves both idioms:
+///   • **compact** (iPhone, and iPad in Slide Over / narrow split) → the five-tab `TabView`.
+///   • **regular** (iPad full-screen / Stage Manager) → the Mac's sidebar + detail split.
+///
+/// Both render the SAME `RemoteStore` projection — the iPad is a third renderer of the one host
+/// authority (UX_MACOS §8), not a fork. The store holds all real state, so a size-class flip
+/// (e.g. resizing a Stage Manager window) only swaps chrome; sessions, connection, and the open
+/// transcript survive it.
+struct AdaptiveRootView: View {
+    @Environment(\.horizontalSizeClass) private var sizeClass
+
+    var body: some View {
+        if sizeClass == .regular {
+            SplitRootView()
+        } else {
+            CompactRootView()
+        }
+    }
+}
+
+// MARK: - Compact (iPhone / narrow multitasking)
+
+/// The original iPhone shell, relocated verbatim from `RootView`: a five-tab `TabView`. A
+/// notification tap routes to the Sessions tab, where `SessionsView` consumes `pendingRoute`
+/// and pushes the detail.
+struct CompactRootView: View {
+    @EnvironmentObject var store: RemoteStore
+    // Initial tab; overridable via NUCLEIC_TAB for offline UI previews.
+    @State private var tab = Int(ProcessInfo.processInfo.environment["NUCLEIC_TAB"] ?? "") ?? 0
+
+    var body: some View {
+        TabView(selection: $tab) {
+            HomeView()
+                .tabItem { Label("Home", systemImage: "house") }.tag(0)
+            SessionsView()
+                .tabItem { Label("Sessions", systemImage: "square.stack.3d.up") }
+                .badge(store.needsYouCount).tag(1)
+            ProjectsView()
+                .tabItem { Label("Projects", systemImage: "folder") }.tag(2)
+            TodosView()
+                .tabItem { Label("To-dos", systemImage: "checklist") }.tag(3)
+            SettingsView()
+                .tabItem { Label("Settings", systemImage: "gearshape") }.tag(4)
+        }
+        // A notification tap routes to its session by jumping to the Sessions tab.
+        .onChange(of: store.pendingRoute) { _, route in
+            if route != nil { tab = 1 }
+        }
+    }
+}
+
+// MARK: - Regular (iPad sidebar + detail)
+
+/// What the sidebar can select. Mirrors the Mac sidebar: a few global destinations plus the
+/// live sessions themselves (grouped by project). Projects are reached through the `projects`
+/// destination (`ProjectsView`), which also hosts the scoped "start a chat here" composer.
+enum SidebarItem: Hashable {
+    case home
+    case projects
+    case todos
+    case settings
+    case session(SessionID)
+}
+
+/// The Mac's information architecture on iPad: a two-column `NavigationSplitView` whose leading
+/// column carries the destinations + the project→session tree, and whose detail is the selected
+/// session (or a destination view). Selection lives here and binds the same `openSessionID`
+/// lifecycle the iPhone push/pop path uses — the detail is keyed by session id so switching one
+/// session for another fires `open`/`closeOpen` exactly as a push/pop would.
+struct SplitRootView: View {
+    @EnvironmentObject var store: RemoteStore
+    @State private var selection: SidebarItem? = .home
+    @State private var columnVisibility: NavigationSplitViewVisibility = .all
+
+    var body: some View {
+        NavigationSplitView(columnVisibility: $columnVisibility) {
+            SplitSidebar(selection: $selection)
+        } detail: {
+            SplitDetail(selection: selection)
+        }
+        .navigationSplitViewStyle(.balanced)
+        // Notification tap → select its session directly (the regular-width analogue of the
+        // compact path's jump-to-Sessions-tab). Then clear the request so it isn't re-consumed.
+        .onChange(of: store.pendingRoute) { _, route in
+            guard let route else { return }
+            selection = .session(route)
+            store.pendingRoute = nil
+        }
+        .onAppear {
+            // Offline UI previews (NUCLEIC_DEMO): open straight into one session.
+            if let raw = ProcessInfo.processInfo.environment["NUCLEIC_DEMO_SESSION"], !raw.isEmpty {
+                selection = .session(SessionID(rawValue: raw))
+            }
+        }
+    }
+}
+
+/// The leading column: global destinations, then the live sessions grouped under their projects
+/// (attention-first within each group), mirroring the Mac sidebar tree. The persistent
+/// connection status sits in the footer — one home for it, versus the phone's per-tab inset.
+private struct SplitSidebar: View {
+    @EnvironmentObject var store: RemoteStore
+    @Binding var selection: SidebarItem?
+
+    /// Live sessions grouped under their project (dashboard order), with anything whose project
+    /// isn't in the dashboard collected into a trailing "Other" group. Attention-first sort.
+    private var projectGroups: [(name: String, rows: [WireSessionSummary])] {
+        let live = store.liveSessions.sorted {
+            let a = StatusStyle.sortRank($0), b = StatusStyle.sortRank($1)
+            return a == b ? $0.updatedAt > $1.updatedAt : a < b
+        }
+        var groups: [(name: String, rows: [WireSessionSummary])] = []
+        var placed = Set<SessionID>()
+        for project in store.dashboard.projects {
+            let rows = live.filter { $0.projectID == project.id.rawValue }
+            guard !rows.isEmpty else { continue }
+            groups.append((project.name, rows))
+            rows.forEach { placed.insert($0.sessionID) }
+        }
+        let orphans = live.filter { !placed.contains($0.sessionID) }
+        if !orphans.isEmpty { groups.append(("Other", orphans)) }
+        return groups
+    }
+
+    var body: some View {
+        List(selection: $selection) {
+            Section {
+                Label("Home", systemImage: "house").tag(SidebarItem.home)
+                Label("Projects", systemImage: "folder").tag(SidebarItem.projects)
+                Label("To-dos", systemImage: "checklist").tag(SidebarItem.todos)
+                Label("Settings", systemImage: "gearshape").tag(SidebarItem.settings)
+            }
+            if projectGroups.isEmpty {
+                Section("Sessions") {
+                    Text(store.connectivity.isLive
+                        ? "Start a session from Home or the Mac to see it here."
+                        : "Waiting to connect to \(store.hostName)…")
+                        .font(.callout).foregroundStyle(.secondary)
+                }
+            } else {
+                ForEach(projectGroups, id: \.name) { group in
+                    Section(group.name) {
+                        ForEach(group.rows, id: \.sessionID) { summary in
+                            SessionRow(summary: summary, showProjectName: false)
+                                .tag(SidebarItem.session(summary.sessionID))
+                                .listRowBackground(SessionRowWash(summary: summary))
+                                .swipeActions(edge: .leading) {
+                                    Button {
+                                        store.setFavorite(summary.sessionID, !summary.favorite)
+                                    } label: {
+                                        Label("Favorite", systemImage: summary.favorite ? "star.slash" : "star.fill")
+                                    }.tint(.yellow)
+                                }
+                                .swipeActions(edge: .trailing) {
+                                    Button(role: .destructive) {
+                                        store.deleteSession(summary.sessionID)
+                                    } label: { Label("Delete", systemImage: "trash") }
+                                    Button {
+                                        store.setArchived(summary.sessionID, !summary.archived)
+                                    } label: {
+                                        Label(summary.archived ? "Unarchive" : "Archive",
+                                              systemImage: summary.archived ? "tray.and.arrow.up" : "archivebox")
+                                    }.tint(.gray)
+                                }
+                        }
+                    }
+                }
+            }
+        }
+        .listStyle(.sidebar)
+        .navigationTitle(store.hostName.isEmpty ? "Nucleic" : store.hostName)
+        .toolbar {
+            ToolbarItem(placement: .primaryAction) {
+                Button { store.refreshSessions() } label: {
+                    Image(systemName: "arrow.clockwise")
+                }
+                .help("Refresh")
+            }
+        }
+        .safeAreaInset(edge: .bottom) {
+            ConnectionChip().padding(.bottom, 10)
+        }
+    }
+}
+
+/// The detail column. A selected session reuses the existing `SessionDetailView` unchanged
+/// (it owns its own subscribe/unsubscribe on appear/disappear); it's keyed `.id(sessionID)` so
+/// switching sessions remounts and drives that lifecycle. The destination views already embed
+/// their own `NavigationStack`, so they're shown directly.
+private struct SplitDetail: View {
+    let selection: SidebarItem?
+
+    var body: some View {
+        switch selection {
+        case .home, .none:
+            HomeView()
+        case .projects:
+            ProjectsView()
+        case .todos:
+            TodosView()
+        case .settings:
+            SettingsView()
+        case .session(let id):
+            NavigationStack {
+                SessionDetailView(sessionID: id)
+            }
+            .id(id)
+        }
+    }
+}

NucleicRemote/NucleicRemote/Views/HomeView.swift

@@ -86,6 +86,9 @@ struct HomeView: View {
                     StartChatComposer()
                 }
                 .padding()
+                // Cap + center the dashboard on a wide iPad so it reads like the Mac home rather
+                // than a stretched phone; a no-op at phone width.
+                .readableColumn()
             }
             .navigationTitle("Home")
             .navigationBarTitleDisplayMode(.inline)

NucleicRemote/NucleicRemote/Views/Layout.swift

@@ -0,0 +1,12 @@
+import SwiftUI
+
+/// Width tuning for the universal layout. In a wide iPad detail column, content designed for a
+/// phone runs edge-to-edge and loses the Mac's comfortable reading measure; `readableColumn`
+/// caps its width and centers it. It's a no-op on the phone and on iPad compact multitasking,
+/// where the available width is already below the cap — so the iPhone layout is unchanged.
+extension View {
+    func readableColumn(_ maxWidth: CGFloat = 820) -> some View {
+        frame(maxWidth: maxWidth, alignment: .leading)
+            .frame(maxWidth: .infinity, alignment: .center)
+    }
+}

NucleicRemote/NucleicRemote/Views/SessionDetailView.swift

@@ -71,7 +71,9 @@ struct SessionDetailView: View {
             Button("Cancel", role: .cancel) {}
         }
         .onAppear { store.open(sessionID) }
-        .onDisappear { store.closeOpen() }
+        // Pass our own id so an iPad split-view A→B switch (which may mount B before A
+        // disappears) unsubscribes A without tearing down B's just-opened state.
+        .onDisappear { store.closeOpen(sessionID) }
     }
 
     /// Whether this session's project is under Nucleic Control (gates Orchestra + autoship).
@@ -297,6 +299,9 @@ struct TranscriptList: View {
                     }
                 }
                 .padding()
+                // Cap the transcript to a readable measure on a wide iPad so lines don't run
+                // edge-to-edge on a 13-inch screen; a no-op at phone width.
+                .readableColumn()
             }
             // A drag on the transcript dismisses the keyboard, so a tall multiline composer can
             // be put away without leaving the session.
@@ -310,26 +315,27 @@ struct TranscriptList: View {
     }
 }
 
-/// The Diff tab with the real patch (the Mac Diff tab, phone form): a per-file summary list
-/// over the unified patch, colored +/− per line, fetched on demand via `fetchDiff`.
+/// The Diff tab, read-only over the on-demand `WireSessionDiff`. On a phone it's a per-file
+/// summary over one scrolling unified patch; on a regular-width iPad it becomes the Mac's
+/// two-pane diff — a selectable file list beside the selected file's patch — exploiting the
+/// wide detail column. Same wire, no new protocol.
 struct SessionDiffView: View {
     let diff: WireSessionDiff?
     let loading: Bool
+    /// Below this available width the two-pane diff would leave the patch too cramped, so we
+    /// keep the phone stack. Picks two-pane on a wide iPad (landscape, or a large iPad) and the
+    /// stack on a phone or a narrow portrait split — based on real width, not just size class.
+    private let twoPaneMinWidth: CGFloat = 700
 
     var body: some View {
         if let diff, diff.stat.filesChanged > 0 {
-            ScrollView {
-                VStack(alignment: .leading, spacing: 14) {
-                    fileList(diff)
-                    PatchText(patch: diff.patch)
-                    if diff.truncated {
-                        Label("Patch truncated — open the Mac for the rest.",
-                              systemImage: "scissors")
-                            .font(.caption).foregroundStyle(.secondary)
+            GeometryReader { geo in
+                if geo.size.width >= twoPaneMinWidth {
+                    SplitDiffView(diff: diff)
+                } else {
+                    stacked(diff)
                 }
             }
-                .padding()
-            }
         } else if loading {
             ProgressView("Fetching diff…")
                 .frame(maxWidth: .infinity, maxHeight: .infinity)
@@ -338,15 +344,110 @@ struct SessionDiffView: View {
         }
     }
 
-    private func fileList(_ diff: WireSessionDiff) -> some View {
+    /// Phone form: the file summary over one scrolling unified patch.
+    private func stacked(_ diff: WireSessionDiff) -> some View {
+        ScrollView {
+            VStack(alignment: .leading, spacing: 14) {
                 VStack(alignment: .leading, spacing: 6) {
-            Text("\(diff.stat.filesChanged) file\(diff.stat.filesChanged == 1 ? "" : "s") changed · +\(diff.stat.added) −\(diff.stat.removed)")
-                .font(.subheadline.weight(.semibold))
+                    DiffStatHeader(stat: diff.stat)
+                    ForEach(diff.files) { DiffFileRow(file: $0) }
+                }
+                .card()
+                PatchText(patch: diff.patch)
+                if diff.truncated { TruncatedPatchNote() }
+            }
+            .padding()
+            .readableColumn()
+        }
+    }
+}
+
+/// iPad form: the Mac's two-pane diff. A tappable file list on the left drives the selected
+/// file's patch on the right. Row taps use a plain `Button` (not `List(selection:)`, whose
+/// single-select tap handling is unreliable outside an edit-mode / split-view context).
+private struct SplitDiffView: View {
+    let diff: WireSessionDiff
+    @State private var selected: String?
+
+    /// The combined patch split into per-file sections, keyed by file path.
+    private var sections: [String: String] { UnifiedPatch.sections(diff.patch, files: diff.files) }
+    private var current: String? { selected ?? diff.files.first?.path }
+
+    var body: some View {
+        HStack(spacing: 0) {
+            fileList
+                .frame(width: 280)
+                .background(Color(.secondarySystemBackground))
+            Divider()
+            patchPane
+                .frame(maxWidth: .infinity, maxHeight: .infinity)
+        }
+        .onAppear { if selected == nil { selected = diff.files.first?.path } }
+        // Keep the selection valid as the diff refetches (files can appear/vanish between turns).
+        .onChange(of: diff.files) { _, files in
+            if selected == nil || !files.contains(where: { $0.path == selected }) {
+                selected = files.first?.path
+            }
+        }
+    }
+
+    private var fileList: some View {
+        ScrollView {
+            LazyVStack(alignment: .leading, spacing: 0) {
+                DiffStatHeader(stat: diff.stat)
+                    .padding(.horizontal, 12).padding(.vertical, 10)
+                    .frame(maxWidth: .infinity, alignment: .leading)
+                Divider()
                 ForEach(diff.files) { file in
+                    Button { selected = file.path } label: {
+                        DiffFileRow(file: file)
+                            .padding(.horizontal, 12).padding(.vertical, 9)
+                            .frame(maxWidth: .infinity, alignment: .leading)
+                            .background(current == file.path
+                                ? Palette.accent.opacity(0.15) : Color.clear)
+                            .contentShape(Rectangle())
+                    }
+                    .buttonStyle(.plain)
+                }
+                if diff.truncated { TruncatedPatchNote().padding(12) }
+            }
+        }
+    }
+
+    @ViewBuilder
+    private var patchPane: some View {
+        if let path = current, let patch = sections[path], !patch.isEmpty {
+            ScrollView { PatchText(patch: patch).padding() }
+        } else if current != nil {
+            // A file with no textual hunk (binary, or a section dropped by patch truncation).
+            ContentUnavailableView(
+                "No preview", systemImage: "doc",
+                description: Text("This file has no textual diff\(diff.truncated ? " in the fetched patch" : "").")
+            )
+        } else {
+            ContentUnavailableView("Select a file", systemImage: "sidebar.left")
+        }
+    }
+}
+
+/// The "N files changed · +A −R" header shared by both diff forms.
+private struct DiffStatHeader: View {
+    let stat: DiffStat
+    var body: some View {
+        Text("\(stat.filesChanged) file\(stat.filesChanged == 1 ? "" : "s") changed · +\(stat.added) −\(stat.removed)")
+            .font(.subheadline.weight(.semibold))
+    }
+}
+
+/// One file's row: status glyph, path, and its +/− counts. Shared by the phone summary and the
+/// iPad file list.
+struct DiffFileRow: View {
+    let file: WireFileDiff
+    var body: some View {
         HStack(spacing: 8) {
-                    Image(systemName: statusIcon(file.status))
+            Image(systemName: DiffStatus.icon(file.status))
                 .font(.caption)
-                        .foregroundStyle(statusColor(file.status))
+                .foregroundStyle(DiffStatus.color(file.status))
             Text(file.path)
                 .font(.caption.monospaced())
                 .lineLimit(1).truncationMode(.middle)
@@ -356,10 +457,9 @@ struct SessionDiffView: View {
         }
     }
 }
-        .card()
-    }
 
-    private func statusIcon(_ status: String) -> String {
+enum DiffStatus {
+    static func icon(_ status: String) -> String {
         switch status {
         case "added", "untracked": "plus.circle"
         case "deleted": "minus.circle"
@@ -367,8 +467,7 @@ struct SessionDiffView: View {
         default: "pencil.circle"
         }
     }
-
-    private func statusColor(_ status: String) -> Color {
+    static func color(_ status: String) -> Color {
         switch status {
         case "added", "untracked": Palette.success
         case "deleted": Palette.danger
@@ -377,6 +476,57 @@ struct SessionDiffView: View {
     }
 }
 
+private struct TruncatedPatchNote: View {
+    var body: some View {
+        Label("Patch truncated — open the Mac for the rest.", systemImage: "scissors")
+            .font(.caption).foregroundStyle(.secondary)
+            .frame(maxWidth: .infinity, alignment: .leading)
+    }
+}
+
+/// Splits a combined `git diff` patch into per-file sections for the iPad's two-pane view.
+enum UnifiedPatch {
+    /// Map from file path to that file's slice of the unified patch. Sections begin at a
+    /// `diff --git a/… b/…` line. When the section count matches `files` we pair positionally
+    /// (the host emits patch and files together, in order); otherwise we key each section by the
+    /// new path parsed from its header. Callers fall back to a "no preview" state on a miss.
+    static func sections(_ patch: String, files: [WireFileDiff]) -> [String: String] {
+        guard patch.contains("diff --git ") else {
+            // A single-file patch with no git header: attribute the whole thing to the sole file.
+            return files.count == 1 ? [files[0].path: patch] : [:]
+        }
+        var chunks: [String] = []
+        var current: [Substring] = []
+        for line in patch.split(separator: "\n", omittingEmptySubsequences: false) {
+            if line.hasPrefix("diff --git ") {
+                if !current.isEmpty { chunks.append(current.joined(separator: "\n")) }
+                current = [line]
+            } else if !current.isEmpty {
+                current.append(line)
+            }
+        }
+        if !current.isEmpty { chunks.append(current.joined(separator: "\n")) }
+
+        var result: [String: String] = [:]
+        if chunks.count == files.count {
+            for (file, chunk) in zip(files, chunks) { result[file.path] = chunk }
+        } else {
+            for chunk in chunks where newPath(chunk) != nil { result[newPath(chunk)!] = chunk }
+        }
+        return result
+    }
+
+    /// The new-side path from a section's `diff --git a/OLD b/NEW` header. Nil when the header is
+    /// absent or the path is quoted/spaced in a way we don't split cleanly.
+    private static func newPath(_ chunk: String) -> String? {
+        guard let header = chunk.split(separator: "\n", maxSplits: 1).first,
+              header.hasPrefix("diff --git "),
+              let bRange = header.range(of: " b/") else { return nil }
+        let path = header[bRange.upperBound...]
+        return path.isEmpty ? nil : String(path)
+    }
+}
+
 /// The unified patch, one `Text` per line with the classic +/− coloring. Lines scroll
 /// horizontally as a block so long lines don't wrap into noise.
 private struct PatchText: View {