Add persistent scratchpads and multi-window session restoration

DESIGN.md

@@ -18,11 +18,12 @@ All panes use standard AppKit split-view behavior, system materials, native focu
 
 - A new or comment-free document begins with the source alone. The comment inspector opens automatically only when a document already contains review threads or the user starts a comment.
 - Standalone files hide the navigator; directory workspaces reveal it. Closing either sidebar gives its space to the document without changing the outer window frame.
-- The initial window uses a generous 1180 × 780 working size when the screen permits. Later launches restore only a usable, on-screen frame, and the document pane remains the elastic region during live resize and full screen.
-- Opening several files—through the Open panel, Finder, or the CLI—places them in native tabs. An empty tab is reused, duplicate paths focus their existing tab, and separate windows remain available with `⌘N`.
+- The initial window uses a generous 1180 × 780 working size when the screen permits. Later launches restore each window to its prior physical display when available, with a usable on-screen fallback when a display is disconnected; the document pane remains the elastic region during live resize and full screen.
+- Opening several files—through the Open panel, Finder, or the CLI—places them in native tabs. An empty start tab is reused, duplicate paths focus their existing tab, and separate windows remain available.
+- `⌘T` creates an editable, automatically saved untitled Markdown scratchpad in the current tab group. `⌘N` creates one in a separate window, and `⌘⇧S` promotes it to an ordinary named Markdown file without changing its tab position.
 - Tabs follow browser conventions: `⌘T`, `⌘W`, `⌃Tab`, `⌃⇧Tab`, and `⌘1`…`⌘9`. Pane focus uses `⌃1`…`⌃3` so it never competes with tab selection.
 - Reader presentation and file-provider change watching begin only after they are requested, away from the main interaction path. Stale reader work is discarded when the user switches files or modes.
-- A normal relaunch restores tabs and lightweight view state, but an explicit CLI target always wins. Persistence is deferred to a utility queue and never joins the first-window path.
+- A normal relaunch restores independent windows, their physical displays, native tab groups and order, the selected window and tab, usable window frames, scratchpad contents, and lightweight editor state. An explicit CLI target always wins. Session persistence is deferred to a utility queue, and scratchpads remain ordinary private Markdown files rather than database records.
 - New comments or replies arriving from another process never steal focus or open the inspector. They add a restrained numeric tab/toolbar signal and a temporary **New** filter until the affected thread is deliberately visited.
 
 ## Typography and color

Docs/ARCHITECTURE.md

@@ -102,10 +102,18 @@ directory indexing, filesystem watching, comparison loading, collaboration
 overviews, and stage presentation are created only when requested so they do
 not join the initial window path.
 
-The application stores only lightweight local presentation state such as open
-tabs, pane visibility, selection, scroll position, and the active thread. An
-explicit file or directory supplied by the user takes precedence over session
-restoration.
+The application stores only lightweight local presentation state such as the
+independent-window and native-tab hierarchy, pane visibility, selection, scroll
+position, display affinity, and the active thread. Stable native restoration
+identifiers let AppKit preserve system-managed window state; custom placement
+metadata provides physical-display continuity and an on-screen fallback when a
+display is unavailable. Untitled scratchpads are ordinary Markdown
+files below the user's private Application Support directory; the session holds
+only their stable identity and presentation state. Scratch contents use the
+same atomic autosave path as named documents, are flushed synchronously during
+a normal quit, and move to the selected destination only after Save As
+succeeds. An explicit file or directory supplied by the user takes precedence
+over session restoration.
 
 ## CLI contract
 

Docs/RELEASE_NOTES.md

@@ -2,7 +2,18 @@
 
 ## Unreleased
 
-No changes yet.
+- Added durable untitled Markdown scratchpads. `⌘T` creates one in the current
+  tab group, `⌘N` creates one in a separate window, and `⌘⇧S` promotes it to a
+  named file. Scratch contents are private file-backed Markdown, autosave while
+  editing, flush synchronously on quit, and require an explicit Save As or
+  discard decision before a nonempty scratchpad tab closes.
+- Expanded session restoration from one flattened tab list to the complete
+  independent-window and native-tab hierarchy, including tab order, selected
+  tabs, usable window frames, cursor and scroll continuity, and open
+  scratchpads. Existing version-1 sessions migrate to a single restored window.
+- Integrated the durable session with native AppKit window restoration.
+  Physical-display identity and relative placement are retained, with an
+  on-screen fallback when a monitor is disconnected or its layout changes.
 
 ## 0.5.1 — native reading and review fixes
 

README.md

@@ -63,6 +63,8 @@ Open a file for quick editing or a directory for a native, lazily loaded navigat
 
 In the app you can:
 
+- create an automatically saved untitled Markdown scratchpad with `⌘T`, or a scratchpad in a separate window with `⌘N`, then promote it to an ordinary file with `⌘⇧S`;
+- return after a normal quit to the same independent windows and displays, tab groups, selected tabs, cursor positions, and scroll positions;
 - edit literal Markdown with restrained syntax cues, delimiter pairing, list continuation, native undo, find, spellcheck, and accessibility support;
 - switch to a bounded, typography-first reader view with `⌘⇧R`;
 - select a passage and comment from the inline affordance, context menu, or `⌘⌥M`;

Resources/Info.plist

@@ -32,6 +32,8 @@
     <string>Copyright © 2026 OpenProse, Inc.</string>
     <key>NSPrincipalClass</key>
     <string>NSApplication</string>
+    <key>NSQuitAlwaysKeepsWindows</key>
+    <true/>
     <key>CFBundleDocumentTypes</key>
     <array>
         <dict>