Moments across up to four pages: stacked in Flow, side by side in Page/Book (BL-0055)

The save sheet gets "+ Previous page" / "+ Next page" (right to left for
rtl in Page/Book) for a picture that runs over several pages. Moments
store a layout (row | column); pages the selected region does not touch
are dropped. Crops, viewer and gallery draw both layouts.

Dialogs now clean up directly instead of waiting for the "close" event,
which a backgrounded page can deliver late (a closed sheet stayed in the
page and M stopped working).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

moments.js

@@ -1,18 +1,19 @@
 'use strict';
 /*
- * Moments: pages, or a region of one or two facing pages, that a reader saved with exactly one category.
+ * Moments: a page, or a region across up to four neighbouring pages, that a reader saved with exactly one category.
+ * `layout` says how those pages sit together: side by side ("row", Page and Book mode) or stacked ("column", Flow).
  * Stored per user in db.moments[user] as a list. A moment points at its pages by version folder and file
  * name (plus the file's SHA-256 for a later relocation), so a re-scan that shifts page numbers never makes it
  * point at the wrong picture: a file that is gone shows as "page moved" instead.
  */
 const CATEGORIES = ['twist', 'hot', 'awesome', 'cute', 'funny', 'feels'];
-const NOTE_MAX = 200, MAX_PER_USER = 5000;
+const NOTE_MAX = 200, MAX_PER_USER = 5000, MAX_PAGES = 4, LAYOUTS = ['row', 'column'];
 
 class MomentError extends Error { constructor(msg) { super(msg); this.code = 400; } }
 const fail = msg => { throw new MomentError(msg); };
 
 const clamp01 = x => Math.min(1, Math.max(0, x));
-// A region is a rectangle in fractions (0–1) of the displayed page, or of both pages of a spread side by side.
+// A region is a rectangle in fractions (0–1) of the displayed page, or of all its pages put together in `layout`.
 // Nothing or a rectangle covering (almost) everything means the whole page.
 function cleanRegion(r) {
   if (r == null) return null;
@@ -29,14 +30,15 @@ function cleanCategory(cat) {
 }
 const cleanNote = note => String(note == null ? '' : note).replace(/\s+/g, ' ').trim().slice(0, NOTE_MAX);
 
-// Page indexes (into the version's full page list) in displayed order, left to right. One page, or two facing pages.
+// Page indexes (into the version's full page list) in displayed order: left to right, or top to bottom.
 function cleanPages(pages, version) {
-  if (!Array.isArray(pages) || pages.length < 1 || pages.length > 2) fail('A moment covers one page or two facing pages.');
+  if (!Array.isArray(pages) || pages.length < 1 || pages.length > MAX_PAGES) fail(`A moment covers 1 to ${MAX_PAGES} pages.`);
   const out = pages.map(Number);
   if (out.some(i => !Number.isInteger(i) || i < 0 || i >= version.pages.length)) fail('Page not found.');
-  if (out.length === 2 && out[0] === out[1]) fail('Page not found.');
+  if (new Set(out).size !== out.length) fail('A page appears twice.');
   return out;
 }
+const cleanLayout = layout => (layout == null ? 'row' : LAYOUTS.includes(layout) ? layout : fail('Invalid page layout.'));
 
 // Where a stored moment's pages are now. Returns null when the chapter, the version or a page file is gone.
 function locate(moment, manga) {
@@ -55,6 +57,7 @@ function view(moment, manga, url) {
   const chapter = at ? at.chapter : manga && manga.chapterById.get(moment.c);
   return {
     id: moment.id, c: moment.c, v: moment.v, cat: moment.cat, note: moment.note || '', t: moment.t, region: moment.region || null,
+    layout: moment.layout || 'row',
     chapter: chapter ? { label: chapter.label, title: chapter.title, book: chapter.book } : { label: moment.c, title: '', book: '' },
     // Story order: chapter position in the manga, then page, then how far down the page the region starts.
     order: [chapter ? manga.chapters.indexOf(chapter) : 1e9, at ? Math.min(...at.pages) : moment.i[0], moment.region ? moment.region.y : 0],
@@ -71,4 +74,4 @@ function storyCompare(a, b) {
   return a.t - b.t;
 }
 
-module.exports = { CATEGORIES, NOTE_MAX, MAX_PER_USER, MomentError, cleanRegion, cleanCategory, cleanNote, cleanPages, locate, view, storyCompare };
+module.exports = { CATEGORIES, NOTE_MAX, MAX_PER_USER, MAX_PAGES, MomentError, cleanRegion, cleanCategory, cleanNote, cleanPages, cleanLayout, locate, view, storyCompare };