import AppKit
import SwiftUI

/// **The board popover** — "the one board-level surface" (03-board-ui.md § Board popover), and the
/// widget in the window's titlebar that opens it.
///
/// **Tabbed since 2026-08-07 — the restructure is complete, all three tab sessions settled.** The
/// symbol/name header stays at the top; below it sit the tabs — **Info**, **Theme**, **Git** — each
/// the settings surface for one aspect of board configuration, each settled in its own dedicated
/// design session: `BoardInfoTabView`, the metrics dossier; `BoardThemeTabView`, the Solid color /
/// Pattern picker (the Background tab's original name, before the same session widened it past the
/// generated-only picker and folded manual styling back out to Style… ⌥⌘S); and `BoardGitTabView`,
/// which the pre-tab body's mode-aware git section rehomed into whole — postures and notes, none of
/// them re-ruled by the move. That tab carried a **Board Settings…** row to a separate sheet until
/// later the same day, when the 2026-07-31 popover/sheet split was reversed and the sheet's contents
/// rehomed into the tab (see below).
///
/// **Tab membership is the git posture's**, and **selection resets to Info on every open** — both
/// the Git session's rulings. Since 12-editions.md ▸ PIVOT 2026-08-07 the first of those is a
/// structural rule with nothing left to exclude: every board carries all three tabs (03 ▸ Board
/// popover, the same-day pivot note) — see `BoardInfoTab`.
///
/// ### One home, deliberately
///
/// The popover has **no toolbar item** (§ Toolbar: "the window-title widget is its committed home
/// … and a second entry would muddy it"). It has exactly two ways in: the widget, and File ▸ Board
/// Info ⌘I, which is the same widget's popover reached from the keyboard (11-command-nexus.md's
/// class **C** — "the keyboard path is reachability … not bindings").
///
/// **And it is the board's only configuration home** (ruled 2026-08-07, reversing the 2026-07-31
/// popover/sheet split): setup briefly lived in a board settings sheet with its own menu command and
/// a row here pointing at it. The sheet is retired, its add-git and commit-identity controls render
/// inline in the Git tab's postures (`BoardGitSetup.swift`), branch creation went back into the
/// switch menu (`BoardGitControls`), and Board ▸ Board Settings… left the menu bar with them. So
/// "one home per control" — the split's own promise — is now satisfied by there being one surface,
/// and ⌘I is the door to all of it.

// MARK: - Presentation state

/// Whether **this window's** board popover is open.
///
/// Per window rather than per board or per app, and that is the point: ⌘I has to mean "the board in
/// front", so the flag travels with the window through the focus system (`FocusedValues.boardInfo`)
/// exactly as the store does. Two board windows each hold their own and can never toggle each
/// other's — which a flag on the store could not promise the day a board is allowed two windows.
///
/// It is also why this is not in `TransientBoardState`: everything there is *board*-scoped and
/// shared with the board's card windows, and a popover living in one window's titlebar is not that.
@MainActor
@Observable
final class BoardInfoPresentation {

    var isPresented = false

    /// ⌘I's whole behaviour and the widget's alike. **Toggling, not opening**: a shortcut aimed at a
    /// disclosure that could only ever open would leave the popover with no keyboard way out.
    func toggle() {
        isPresented.toggle()
    }
}

/// The focused board window's popover, beside `FocusedValues.boardStore` — see that key for why
/// board-window menu items reach their window this way rather than through the app model.
struct FocusedBoardInfoKey: FocusedValueKey {
    typealias Value = BoardInfoPresentation
}

extension FocusedValues {
    var boardInfo: BoardInfoPresentation? {
        get { self[FocusedBoardInfoKey.self] }
        set { self[FocusedBoardInfoKey.self] = newValue }
    }
}

// MARK: - The window-title widget

/// The titlebar widget: the board's glyph beside a two-line identity block — its name, and on a
/// git-mode board its branch under the name — with a trailing disclosure chevron, whose one job is
/// this popover.
///
/// **A two-line stack since 2026-08-07** (03-board-ui.md ▸ Board popover, the window-title widget
/// passage). It was one line reading `glyph  Title — branch  ⌄`, and the em-dash was the tell: a
/// separator doing a *hierarchy's* job, with the branch competing for the same width as the name it
/// qualifies. So the branch moved under the title in its own smaller, secondary line, the em-dash
/// retired, and the glyph grew to span both lines — an icon sized to the block it labels rather than
/// to whichever line it happened to sit on. A board with no branch is the single title line, vertically
/// centred beside the same glyph, which is the same block with one row.
///
/// **The popover is anchored to the widget itself** — it hangs from the button rather than from the
/// window or the board — which is what makes the affordance and the surface read as one thing. A
/// `.popover` rather than a hand-driven `NSPopover` because SwiftUI's is already transient (a click
/// outside dismisses it), and because the content is SwiftUI either way; the AppKit half of this is
/// only the *placement* (`boardInfoTitlebarAccessory`).
///
/// **Whole-area clickable, not just the chevron** (the card that widened this from a 20×18 chevron
/// button to the full name/branch/chevron button): the title and branch strings sit inside the same
/// `Button`, so a click anywhere across the board's name — or its branch, when shown — opens the
/// popover exactly as a click on the chevron always has.
struct BoardInfoWidget: View {

    let store: BoardStore
    let recents: StyleRecents

    /// The git state this board's **session** composed with — read once, at the moment the widget is
    /// installed, and never re-derived (12-editions.md ▸ The entitlement: "a lapse never interrupts
    /// an open session"). `git` is a reference type and `@Observable`, so add-git flipping the mode,
    /// or a branch switch, redraws the widget without anything here being re-created.
    ///
    /// It stopped being a tier signal at 12 ▸ PIVOT 2026-08-07 — every session composes a git state
    /// now, whatever the tier — so a `nil` here means only "this caller had no session to hand over"
    /// (previews, the accessory-installation tests), which reads as mode `none`.
    let git: HistoryStore?

    @Bindable var presentation: BoardInfoPresentation

    /// The widget's two strings, computed fresh on every body evaluation rather than cached anywhere.
    /// That matters here specifically: `boardInfoTitlebarAccessory` builds this view exactly **once**
    /// at install, so a value read anywhere but inside `body` would freeze at the widget's birth and
    /// never see a later rename or branch switch. `store.snapshot` and `git.branch` are both
    /// `@Observable`, so reading them here is what makes the title and branch live.
    private var summary: BoardInfoTitlebarSummary {
        BoardInfoTitlebarSummary(
            snapshotTitle: store.snapshot.title.value,
            rootURL: store.rootURL,
            mode: git?.mode ?? .none,
            branch: git?.branch
        )
    }

    var body: some View {
        Button {
            presentation.toggle()
        } label: {
            HStack(spacing: 6) {
                // The board's own glyph beside its name — the identity pair the popover header
                // states, restated where the board is named all day (2026-08-07). Read inside
                // `body` for `summary`'s reason: `icon`/`iconColor` are `@Observable` fields, so a
                // restyle from the popover repaints this widget without reinstalling it. Lenient on
                // both dimensions — an unresolvable glyph draws the board default, an unresolvable
                // tint draws the standard secondary.
                //
                // **Its own font, not the container's** (the two-line rework, 2026-08-07): at 22pt
                // it draws about twice the height `.imageScale(.small)` gave it on the container's
                // 13pt, which is what lets one glyph span the title and branch lines instead of
                // sitting beside the upper one. The number is the icon's own size rather than a
                // scale factor because that is the dimension being chosen — the block's height.
                Image(systemName: ItemSymbol.name(store.snapshot.icon, fallback: ItemSymbol.board))
                    .font(.system(size: 22))
                    .foregroundStyle(iconTint)
                    // Decorative beside the name it repeats — the button's own label already says
                    // everything VoiceOver needs (`accessibilityLabel` below).
                    .accessibilityHidden(true)

                // The identity block: the name, and the branch beneath it on a git-mode board. On
                // any other board this is the single title line and the `HStack`'s own centring puts
                // it level with the glyph — the stack is the same shape with one row, never a
                // special case.
                VStack(alignment: .leading, spacing: 1) {
                    Text(summary.title)
                        // Styled like a titlebar title, because that is what it now stands in for
                        // (`BoardWindowHost` hides the system title display in favor of this widget).
                        .font(.system(size: 13, weight: .semibold))
                        .foregroundStyle(.primary)
                        .lineLimit(1)
                        .truncationMode(.tail)

                    if let branch = summary.branch {
                        // Smaller and secondary — the qualifier under the name it qualifies. The
                        // em-dash that separated the two on one line retired with the stack: a
                        // hierarchy that a layout can state does not need punctuation to state it.
                        Text(branch)
                            .font(.system(size: 11))
                            .foregroundStyle(.secondary)
                            .lineLimit(1)
                            .truncationMode(.tail)
                    }
                }
                // Yields space to the chevron first when the block doesn't fit inside the width cap
                // below — the board's identity is the more load-bearing half of the pair, and both
                // its lines truncate rather than the disclosure disappearing.
                .layoutPriority(1)

                Image(systemName: "chevron.down")
                    .imageScale(.small)
                    .fontWeight(.semibold)
                    .foregroundStyle(.secondary)
            }
            .font(.system(size: 13))
            // A long board name (or branch) must not swallow the whole titlebar — capped rather
            // than left to grow, with the truncation above doing the rest. The height is the
            // two-line block's (2026-08-07; it was the original chevron's 18 while the widget was
            // one line), which is what keeps the accessory titlebar-appropriate: tall enough for
            // name-over-branch, and no taller than a standard title bar carries.
            .frame(maxWidth: 400, alignment: .leading)
            .frame(height: 32)
            .contentShape(Rectangle())
        }
        .buttonStyle(.plain)
        .help("Board Info")
        .accessibilityLabel(accessibilityLabel)
        .accessibilityHint("Shows board info")
        // Populates the branch line the moment a git-mode board's window opens, rather than waiting
        // on the popover's own read (`BoardGitControls`'s `.task`, which only runs once the popover
        // has actually been opened once). The widget is on screen from the start, so it is the
        // earlier honest place to ask; `refreshBranch()` is already a no-op outside git mode, so this
        // costs nothing on the other four postures.
        .task { await git?.refreshBranch() }
        .popover(isPresented: $presentation.isPresented, arrowEdge: .bottom) {
            BoardInfoView(store: store, recents: recents, git: git)
        }
    }

    /// What VoiceOver reads for the button, now that it says more than "Board Info": the board's
    /// name, plus the branch when the widget is showing one — `.help` keeps the shorter "Board Info"
    /// wording as the hover tooltip, and `.accessibilityHint` on the widget itself still names what
    /// the button does.
    private var accessibilityLabel: String {
        guard let branch = summary.branch else { return summary.title }
        return "\(summary.title), branch \(branch)"
    }

    /// The widget glyph's tint: the board's `iconColor` where it resolves, the quiet secondary
    /// otherwise — `CardFaceView`'s `iconTint` rule at the board's own level.
    private var iconTint: AnyShapeStyle {
        if let color = Palette.color(for: store.snapshot.iconColor) {
            return AnyShapeStyle(color)
        }
        return AnyShapeStyle(.secondary)
    }
}

// MARK: - The widget's strings

/// **The window-title widget's two strings, as one pure function** of the board's on-disk title, its
/// folder, and the session's git posture — pulled out so the fallback rule and the branch-visibility
/// rule are each assertable without a widget on screen (`BoardInfoTitlebarSummaryTests`), the same
/// reason `BoardGitSection.resolve` exists over in `BoardGitTabView.swift`.
///
/// **Title.** `AppModel.displayName(of:)` is the same rule applied to the window's actual title
/// (`BoardWindowHost.windowTitle` reads it, and `.navigationTitle` keeps feeding it to the Window
/// menu, Exposé, VoiceOver and restoration even though the title bar's own rendering of it is now
/// hidden — see `BoardWindowHost.configureWindow`): the on-disk `title`, falling back to the folder
/// name sans extension when absent or empty (01-storage-format.md § Board naming). Restated here
/// against the raw title string and `rootURL` rather than a `BoardStore`, so this seam is testable
/// with plain values and no fixture board on disk — the one duplication this card leaves behind
/// rather than reshaping `AppModel.displayName(of:)`'s signature to fit both call sites.
///
/// **Branch.** Shown only when the board is actually git-mode — `mode == .git` with a non-`nil`
/// branch — the same condition `BoardGitSection.resolve`'s `.branch` case covers. **The tier clause
/// is gone** (12-editions.md ▸ PIVOT 2026-08-07: git is tier-independent, so a git-mode board is a
/// git-mode board and the widget says so on every tier); the rule it read `tier == .pro && mode ==
/// .git` until that day is recorded here rather than restated in code. A board with no repository or
/// an inert one (mode `.none`, `.repoNested`, `.unverifiable`) shows no branch; neither does a
/// git-mode board whose branch has not been read yet (`HistoryStore.branch` starts `nil` until
/// `refreshBranch()` answers, which the widget's own `.task` kicks off at open).
struct BoardInfoTitlebarSummary: Equatable {

    let title: String
    let branch: String?

    init(snapshotTitle: String?, rootURL: URL, mode: BoardGitMode, branch: String?) {
        if let snapshotTitle, !snapshotTitle.isEmpty {
            self.title = snapshotTitle
        } else {
            self.title = rootURL.deletingPathExtension().lastPathComponent
        }
        self.branch = mode == .git ? branch : nil
    }
}

/// The widget wearing AppKit's clothes, because SwiftUI has no way to put a view in the titlebar:
/// an `NSTitlebarAccessoryViewController` hosting the button, laid out `.leading` so it sits in the
/// title bar beside the window title rather than in the window's content.
///
/// `HostedWindowController.installTitlebarAccessory` owns the rest of the lifecycle — one per
/// window, removed on detach — for the same reason it owns the delegate proxying: the window is
/// SwiftUI's, and anything hung on it has to be taken back off.
@MainActor
/// `git` defaults to no session, so that a caller with none in hand (the accessory-installation
/// tests, which are about AppKit plumbing rather than about git) describes a board honestly rather
/// than by accident: a Git tab in its no-repository posture, and a widget with no branch line. The
/// app's own call site passes the session's value explicitly.
func boardInfoTitlebarAccessory(
    store: BoardStore,
    recents: StyleRecents,
    git: HistoryStore? = nil,
    presentation: BoardInfoPresentation
) -> NSTitlebarAccessoryViewController {
    let hosting = NSHostingView(
        rootView: BoardInfoWidget(
            store: store,
            recents: recents,
            git: git,
            presentation: presentation
        )
    )
    // The titlebar lays its accessories out by fitting size, and a hosting view that measured itself
    // as zero would be an invisible, unclickable widget. `.intrinsicContentSize` re-measures on every
    // SwiftUI update, so this starting frame only has to survive the first layout pass before the
    // widget's real content replaces it — but that first pass is exactly what a 20×18 placeholder
    // (the old chevron-only width) would clamp now that the widget's content can run out to 400pt:
    // wide enough that the widest realistic first paint is never visibly clipped before the resize.
    // The height is the widget's own two-line figure (2026-08-07), for the same reason the width is
    // generous — a first pass clamped to the old one-line 18 would paint a clipped block.
    hosting.sizingOptions = [.intrinsicContentSize]
    hosting.frame = NSRect(x: 0, y: 0, width: 200, height: 32)

    let controller = NSTitlebarAccessoryViewController()
    controller.view = hosting
    controller.layoutAttribute = .leading
    return controller
}

// MARK: - Tabs

/// The popover's aspects, one tab each (03-board-ui.md § Board popover, the 2026-08-07 tab
/// restructure — all three original sessions settled): **Info** (`BoardInfoTabView`), **Theme**
/// (`BoardThemeTabView`), **Git** (`BoardGitTabView`) — and **Sync** (`BoardSyncTabView`), added
/// 2026-08-07 as a standing placeholder: the strip claims the position now, the surface says
/// honestly that nothing lives there yet, and 07-sync-collab.md's cards are where its contents get
/// ruled. The raw values are the segmented control's own labels, so the strip needs no separate
/// label function.
enum BoardInfoTab: String, CaseIterable, Identifiable {

    case info = "Info"
    case theme = "Theme"
    case git = "Git"
    case sync = "Sync"

    var id: Self { self }

    // **Membership is the git posture's, and the posture never says "absent" any more.** The Git
    // session ruled (2026-08-07) that the Git tab joins the strip only where `BoardGitSection` has
    // something true to say, which then meant dropping it on a free board with no `.git` — the
    // "absent, no placeholder" rule carried up to the strip. **12-editions.md ▸ PIVOT 2026-08-07**,
    // the same day, retired the free-only postures wholesale: git left the paywall, `.absent` and
    // `.proPointer` died with it, and 03-board-ui.md ▸ Board popover records the consequence — "the
    // absent posture is unreachable and every board carries all three tabs. The membership rule
    // stands structurally — the strip still asks the posture — it just never hears 'absent'
    // anymore." So there is no `available(…)` filter here to ask it with: membership is `allCases`,
    // in `allCases`' own order (Info, Theme, Git, Sync), which is what the filter answered anyway.
}

// MARK: - The popover's content

/// The symbol/name header, then the tab bar, then the selected tab's surface — one view
/// (03-board-ui.md § Board popover).
///
/// Width is the style editor's — the number that keeps the Style… popover narrow enough to sit
/// beside a card — kept through the restructure so the popover's footprint didn't wander while the
/// tabs filled in; all three settled tabs (Info, Theme, Git) kept it, so whether the tabbed surface
/// ever wants its own width remains open, but nothing has needed one yet.
struct BoardInfoView: View {

    let store: BoardStore
    let recents: StyleRecents
    let git: HistoryStore?

    /// The selected tab, and **it resets to Info on every open** — a ruling, not an accident (the
    /// Git session, 2026-08-07, closing the question the earlier tab sessions deferred): the popover
    /// is transient and Info is the board's face, and a remembered tab could strand selection on a
    /// tab the next board's posture doesn't offer. `@State` on the popover's content, which
    /// `BoardInfoWidget` hands `.popover` fresh on every open, is exactly that rule and nothing more.
    @State private var tab: BoardInfoTab = .info

    /// The style editor brings its own padding, so the sections around it carry the same number by
    /// hand instead of an outer padding that would double up on it — **the editor's own figure**
    /// (`StyleEditorLayout.sectionSpacing`), which is font-derived, so the popover's chrome scales
    /// with the grids inside it (10-accessibility.md's full-relative-scaling rule).
    private var inset: CGFloat {
        StyleEditorLayout.sectionSpacing(bodyPointSize: CardWindowMetrics.bodyPointSize)
    }

    init(
        store: BoardStore,
        recents: StyleRecents,
        git: HistoryStore? = nil
    ) {
        self.store = store
        self.recents = recents
        self.git = git
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            VStack(alignment: .leading, spacing: 6) {
                HStack(spacing: 6) {
                    // The board's own icon, inline with its name — the same field the embedded style
                    // editor's symbol section below writes, offered here too since a board's identity
                    // is its name *and* its glyph together (03-board-ui.md § Styling ▸ Controls). No
                    // `undo:` — the board popover has none of its own, so this reaches the board's
                    // stack exactly as the embedded editor's writes do.
                    SymbolPicker(
                        current: store.snapshot.icon.value,
                        fallback: ItemSymbol.board,
                        onSelect: { name in
                            StyleCommand.apply(
                                icon: name.map { StyleChange.set($0) } ?? .remove,
                                to: .board,
                                in: store,
                                recents: recents
                            )
                        },
                        // The colour row — the picker's 4×2 tint grid, writing `iconColor` through
                        // the same funnel the glyph writes `icon`: None removes the key, a well
                        // writes the palette name (2026-08-07).
                        currentColor: store.snapshot.iconColor.value,
                        onSelectColor: { name in
                            StyleCommand.apply(
                                iconColor: name.map { StyleChange.set($0) } ?? .remove,
                                to: .board,
                                in: store,
                                recents: recents
                            )
                        }
                    )
                    .disabled(!store.acceptsBoardMutations)
                    BoardRenameField(store: store)
                }
            }
            .padding(inset)

            Divider()

            // The tab bar: a segmented control rather than a `TabView`, because the popover is a
            // compact settings surface and the segmented idiom is the macOS shape for switching
            // between a handful of peer panes inside one. The label is hidden visually but stays
            // the control's accessibility name. It iterates `allCases` — the strip's membership is
            // still the board's git posture in principle (the Git session's ruling), and since
            // 12-editions.md ▸ PIVOT 2026-08-07 that posture is never "absent", so every board
            // carries the whole strip (03-board-ui.md ▸ Board popover, the same-day pivot note).
            Picker("Board configuration", selection: $tab) {
                ForEach(BoardInfoTab.allCases) { tab in
                    Text(tab.rawValue)
                }
            }
            .pickerStyle(.segmented)
            .labelsHidden()
            .padding(.horizontal, inset)
            .padding(.top, inset)

            // The selected tab's surface — the first three settled 2026-08-07, each in its own
            // dedicated session and its own file; Sync is that day's standing placeholder. Each pads
            // itself by `inset`, so the switch adds nothing.
            switch tab {
            case .info:
                BoardInfoTabView(store: store, inset: inset)
            case .theme:
                BoardThemeTabView(store: store, inset: inset)
            case .git:
                BoardGitTabView(store: store, git: git, inset: inset)
            case .sync:
                BoardSyncTabView(inset: inset)
            }
        }
        // The style editor's popover width, taken from the editor rather than restated — the number
        // that keeps a compact settings popover narrow enough to sit beside a card. It is
        // font-derived, so the whole surface scales with the grids inside it (10-accessibility.md).
        .frame(width: StyleEditorLayout.popover(bodyPointSize: CardWindowMetrics.bodyPointSize).width)
    }
}

// MARK: - Rename

/// The board rename field (03-board-ui.md § Board popover; 01-storage-format.md § Board naming).
///
/// The exits are the inline editors' — Return and focus loss commit, Escape abandons — but the
/// **placeholder is the whole of the board-naming rule made visible**: an empty field shows the
/// folder name, because that is what the window title will say, and committing empty is how a user
/// asks for exactly that. "Untitled" appears nowhere; boards do not have it.
///
/// **It is not born focused**, unlike the three inline editors. Those are each opened by a gesture
/// that means "edit this now"; this one is one control among several on a configuration surface,
/// where the keyboard path is Tab-reachability rather than a caret waiting in the first field
/// (11-command-nexus.md's class **C**).
///
/// Every handler is idempotent, for `InlineTitleField`'s reason: the exits overlap by construction —
/// Return commits and then something takes focus, which fires the focus-loss commit an instant
/// later — and `BoardStore.renameBoard` skips an unchanged title, so the second call writes nothing.
private struct BoardRenameField: View {

    let store: BoardStore

    @State private var draft = ""
    @FocusState private var isFocused: Bool

    var body: some View {
        TextField(fallbackName, text: $draft)
            .textFieldStyle(.roundedBorder)
            .lineLimit(1)
            .focused($isFocused)
            .onSubmit { store.renameBoard(draft) }
            // **Escape steps outward one layer per press** (04-interactions.md ▸ Grammar): a dirty
            // field abandons its edit and keeps the popover open, and an unedited one lets the press
            // through to the popover's own dismissal. Reverting first is also what makes a dismissal
            // safe on the paths where the press never reaches here — the focus-loss commit that
            // follows sees a draft equal to what is on disk and writes nothing.
            .onKeyPress(.escape) {
                guard draft != committed else { return .ignored }
                draft = committed
                return .handled
            }
            .onChange(of: isFocused) { _, focused in
                guard !focused else { return }
                store.renameBoard(draft)
            }
            .onAppear { draft = committed }
            // A foreign rename — an agent, a hand edit, a sync — landing behind an open popover
            // updates the field, but never under the user's fingers: a draft being typed is the
            // user's, and the reload is not an edit to it (02-architecture.md § Live-reload
            // resilience, the same courtesy the inline editors get by tracking their UUID).
            .onChange(of: committed) { _, title in
                guard !isFocused else { return }
                draft = title
            }
            // The popover can be dismissed without the field ever reporting focus loss, and a
            // dismissal is a commit like any other click-away. Idempotent with the handler above.
            .onDisappear { store.renameBoard(draft) }
            // The read-only lock disables every mutating surface (02-architecture.md § The lock's
            // scope) — and the popover *stays open* under it, which is the style popover's settled
            // precedent: the lock is a condition the banner is already explaining, not a reason to
            // yank a surface away. `acceptsBoardMutations` rather than `isReadOnly` alone so this
            // field and the editor below it disable as one surface rather than in halves.
            .disabled(!store.acceptsBoardMutations)
    }

    /// The `title` on disk, as the last reload read it — "" for a board that has none.
    private var committed: String { store.snapshot.title.value ?? "" }

    /// The folder name, sans extension: what the window title shows when `title` is absent
    /// (01-storage-format.md § Board naming), and therefore the honest thing for an empty field to
    /// promise. Read off `rootURL` rather than `snapshot.rootURL` so a Finder rename absorbed
    /// mid-session shows here immediately.
    private var fallbackName: String {
        store.rootURL.deletingPathExtension().lastPathComponent
    }
}