Build the Raw Source outlet

The escape hatch: View > Raw Source (opt-cmd-E) unmounts the whole
content area for the literal on-disk index.md in a plain monospaced
editor with Cancel/Apply. Raw source is window-level state, not a third
body mode — entry rides setMode(.preview), which flushes the Edit
session by construction, then reads the file fresh; exit reveals
Preview, and an empty body after Apply does not reopen Edit (openIfNeeded
already ran). Apply validates the proposed bytes through the loader's
own card checks — parseDocument's strict UTF-8/BOM rejection, schema,
order — deliberately skipping the uneditable-shape refusal, since a
flow-mapping card is exactly what the hatch repairs; invalid bytes
alert in place with the loader's own error and no bracket opens. The
write is byte-for-byte with no modified stamp and no modified-by clear,
per 01's explicit carve-out — the verbatim contract outranks stamping —
and identical bytes write nothing. Escape cancels, cmd-Return applies,
toggle-off applies too, and cmd-E disables while raw is active via a
testable predicate. Tombstoned targets refuse as vanished: a foreign
delete is never reverted by a stale buffer.

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

Kanban/UI/Card/CardWindowView.swift

@@ -9,11 +9,11 @@ import SwiftUI
 ///
 /// The *shell*: the two columns, their scrolling, the sidebar's fixed width, and the read-only
 /// renderings of what the loader already knows — the card's title and its created/modified line —
-/// over the body column's two live surfaces (Preview and Edit, `CardBodySurface`). Everything that
+/// over the body column's two live surfaces (Preview and Edit, `CardBodySurface`), with the
+/// raw-source outlet swapping the pair of columns out entirely when it is active. Everything that
 /// reads or writes beyond that is later work and is marked where it lands:
 ///
 /// - the title as an editable field (commit on Return / focus loss, Escape abandons),
-/// - the raw-source outlet,
 /// - the sidebar's five sections, which are section *headers* here and nothing more.
 ///
 /// The placeholders are structural rather than apologetic: the sidebar's inventory and its order are
@@ -47,6 +47,9 @@ struct CardWindowView: View {
     /// it, Preview renders it, and `adopt(diskBody:)` below is where the snapshot gets a say —
     /// which is exactly the point at which dirty-buffer-wins is decided.
     let bodySession: CardBodyEditSession
+    /// This window's raw-source outlet. While it is active the two columns are gone entirely — see
+    /// `body`.
+    let rawSource: CardRawSourceSession
     /// Whether a checkbox may write — `false` under the board's read-only lock.
     let isEditable: Bool
     /// Commits a checkbox flip: the marker's byte offset in the body, and the state the user saw.
@@ -57,18 +60,35 @@ struct CardWindowView: View {
     /// together when the system text size changes.
     private var bodyPointSize: CGFloat { CardWindowMetrics.bodyPointSize }
 
+    /// The two columns — **or the raw-source editor in place of both of them**.
+    ///
+    /// A swap rather than an overlay, which is 05 ▸ Raw source outlet's own word for it ("swaps the
+    /// **entire content area — title, body, and sidebar —** for the literal on-disk `index.md`") and
+    /// what the rule underneath it requires: the same frontmatter is being edited as raw text, so a
+    /// sidebar still offering to restyle the card, or a title field still writing to `title`, would
+    /// be two editors racing for one file. Unmounting them is the only version of "they can't fight"
+    /// that cannot be got wrong later.
+    ///
+    /// The cost is one thing and it is accepted: the body editor's scroll position and selection do
+    /// not survive a round trip through source mode, because its text view genuinely goes away. What
+    /// does survive is the buffer, which is the Edit session's, not the view's — and it was flushed
+    /// to disk on the way in regardless.
     var body: some View {
-        HStack(spacing: 0) {
-            bodyColumn
-                .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
+        if rawSource.isActive {
+            CardRawSourceView(session: rawSource, presentation: bodyPresentation)
+        } else {
+            HStack(spacing: 0) {
+                bodyColumn
+                    .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
 
-            Divider()
+                Divider()
 
-            sidebar
-                // Fixed, and the one place it comes from.
-                .frame(width: CardWindowMetrics.sidebarWidth(bodyPointSize: bodyPointSize))
-                .frame(maxHeight: .infinity, alignment: .top)
-                .background(.background.secondary)
+                sidebar
+                    // Fixed, and the one place it comes from.
+                    .frame(width: CardWindowMetrics.sidebarWidth(bodyPointSize: bodyPointSize))
+                    .frame(maxHeight: .infinity, alignment: .top)
+                    .background(.background.secondary)
+            }
         }
     }