Build Preview mode rendering

The card body's resting state: swift-markdown (pinned 0.8.0, smart
typography off — Preview renders the bytes on disk) parsed into a pure
BodyMarkup model with UTF-8 source offsets, rendered on one hosted
TextKit 1 NSTextView — chosen because find-in-text is NSTextFinder,
checkbox clicks reuse AppKit character hit-testing, links are .link
attributes, and NSTextTable's automatic layout is exactly the
columns-sized-to-contents rule. The GFM subset renders per 05; HTML
stays verbatim code-styled text; relative images resolve against the
card folder while remote URLs are never fetched, drawing a quiet chip
instead. Task checkboxes are live: a click flips exactly one byte
through a fresh-read, refuse-uneditable, stamp, atomic-replace write —
the app's only offset-addressed write, so a moved target refuses as
staleTarget and what the user saw decides the direction, netting one
toggle on a double-click. Empty bodies open in Edit per CardBodyMode's
opening rule, applied once; the Edit surface itself stays an honest
read-only stub until its card. FindCommand prefers the card body's
find over board search when a card window is focused.

Claude-Session: https://claude.ai/code/session_01SR4XGjmBE16ZUYWpfFHXwY

Kanban/App/CardWindowHost.swift

@@ -89,6 +89,9 @@ struct CardWindowHost: View {
     @State private var windowController = HostedWindowController()
     @State private var session = CardWindowSession()
     @State private var phase: Phase = .opening
+    /// This window's body column — the Preview/Edit mode, and the ⌘F hook a menu item reaches
+    /// through the focus system (`CardBodyPresentation`).
+    @State private var bodyPresentation = CardBodyPresentation()
 
     private enum Phase {
         case opening
@@ -149,6 +152,10 @@ struct CardWindowHost: View {
             // rename retitles the window and a lane move re-subtitles it with no notification of
             // our own (05-card-window.md ▸ Window).
             .navigationSubtitle(windowSubtitle)
+            // Edit ▸ Find (⌘F) is find-in-text in a card window (11-command-nexus.md) — the menu
+            // item reaches the frontmost one's body surface through this, exactly as board-window
+            // items reach their window's store (`FocusedBoardStoreKey`).
+            .focusedSceneValue(\.cardBody, bodyPresentation)
             .task { start() }
             .onChange(of: shouldDismiss, initial: true) { _, dismisses in
                 guard dismisses else { return }
@@ -163,14 +170,37 @@ struct CardWindowHost: View {
 
     @ViewBuilder
     private var content: some View {
-        if let placement {
-            CardWindowView(card: placement.card)
+        if case let .open(store) = phase, let placement {
+            CardWindowView(
+                card: placement.card,
+                cardFolder: Self.cardFolder(root: store.rootURL, placement: placement),
+                bodyPresentation: bodyPresentation,
+                // "Under the read-only lock the controls disable in place — an in-content mutation
+                // menu validation can't reach" (05 ▸ Preview). The checkbox is that control, and
+                // the store's own lock is the whole predicate.
+                isEditable: !store.isReadOnly,
+                onToggleTask: { offset, checked in
+                    store.toggleTaskMarker(inCard: placement.card.id, bodyOffset: offset, checked: checked)
+                }
+            )
         } else {
             // Nothing to render and nothing worth animating: this window is on its way out.
             Color.clear
         }
     }
 
+    /// `<root>/<lane>/<card>` — the card's own folder, which is what its body's relative images and
+    /// links resolve against (05-card-window.md ▸ Preview).
+    ///
+    /// Built off the store's *current* `rootURL` rather than the ref's captured one, for
+    /// `BoardStore.liveItem`'s reason: a mid-session folder rename moves the board, and a preview
+    /// resolving images against where the board used to be would quietly stop showing them.
+    static func cardFolder(root: URL, placement: CardPlacement) -> URL {
+        root
+            .appendingPathComponent(placement.lane.id.rawValue, isDirectory: true)
+            .appendingPathComponent(placement.card.id.rawValue, isDirectory: true)
+    }
+
     /// Where this window's card is in this board's snapshot, or `nil` when it is not — which is the
     /// same condition `shouldDismiss` reads, one moment before the window goes.
     private var placement: CardPlacement? {