@@ -0,0 +1,10 @@
+---
+'@object-ui/app-shell': patch
+---
+
+fix(console): the sidebar's fold width is derived from the record drawer over the list, now that the split pane is retired
+
+Clause-②: no
+Metadata-protocol: none
+
+The console sidebar still folds to its icon rail below 1416 px, and nothing changes at any width: a 1280 px or 1366 px window keeps the rail, a click still expands it over the content, and "Keep sidebar open" still keeps it expanded. What changes is the reason the code gives for 1416. It was the split pane beside the list, which is retired. It is now the record drawer a list record opens in (720 px, non-modal, so the list beside it stays readable and clickable), the narrowest list that still draws its columns beside it (440 px), and the expanded sidebar (256 px). The module-internal `RECORD_SPLIT_MIN_CONTENT_WIDTH` is now `RECORD_DRAWER_MIN_CONTENT_WIDTH`, built from `RECORD_DRAWER_WIDTH` and `LIST_MIN_COLUMNS_WIDTH`; none of them is exported from the package entry.
@@ -1,21 +1,26 @@
 // Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
 
 /**
- * consoleSidebarRail — the fold width is derived from the sidebar it folds
- * (objectstack#27593). `CONSOLE_EXPANDED_SIDEBAR_WIDTH` restates the sidebar
- * primitive's `--sidebar-width`, so this reads the primitive's value off a
- * mounted provider and holds the two equal: a wider or narrower sidebar moves
- * the fold width with it, or this goes red.
+ * consoleSidebarRail — the fold width is derived from what covers the content
+ * and from the sidebar it folds (objectstack#27593, re-derived on
+ * objectstack#29109 once the split pane retired). `CONSOLE_EXPANDED_SIDEBAR_WIDTH`
+ * restates the sidebar primitive's `--sidebar-width` and `RECORD_DRAWER_WIDTH`
+ * restates plugin-view's default drawer width, so this reads both off their
+ * owners and holds them equal: a wider or narrower sidebar or drawer moves the
+ * fold width with it, or this goes red.
  */
 
 import '@testing-library/jest-dom/vitest';
 import { render } from '@testing-library/react';
 import { SidebarProvider } from '@object-ui/components';
+import { overlayWidthFor } from '@object-ui/plugin-view';
 import { describe, expect, it } from 'vitest';
 import {
   CONSOLE_EXPANDED_SIDEBAR_WIDTH,
   CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH,
-  RECORD_SPLIT_MIN_CONTENT_WIDTH,
+  LIST_MIN_COLUMNS_WIDTH,
+  RECORD_DRAWER_MIN_CONTENT_WIDTH,
+  RECORD_DRAWER_WIDTH,
 } from '../consoleSidebarRail';
 
 /** A CSS length in px: `rem` against the 16 px root the console renders at. */
@@ -26,24 +31,59 @@ function toPx(length: string): number {
   return match![2] === 'rem' ? value * 16 : value;
 }
 
-describe('the console sidebar fold width (objectstack#27593)', () => {
+/** The sidebar primitive's expanded and rail widths, read off a mounted provider. */
+function primitiveSidebarWidths(): { expanded: number; rail: number } {
+  const { container } = render(
+    <SidebarProvider>
+      <div />
+    </SidebarProvider>,
+  );
+  const wrapper = container.firstElementChild as HTMLElement;
+  return {
+    expanded: toPx(wrapper.style.getPropertyValue('--sidebar-width')),
+    rail: toPx(wrapper.style.getPropertyValue('--sidebar-width-icon')),
+  };
+}
+
+/** The list left beside the open drawer in a window `width` px wide, the sidebar `sidebar` px wide. */
+function listBesideDrawer(width: number, sidebar: number): number {
+  return width - sidebar - RECORD_DRAWER_WIDTH;
+}
+
+describe('the console sidebar fold width (objectstack#27593, #29109)', () => {
   it('restates the primitive’s expanded sidebar width', () => {
-    const { container } = render(
-      <SidebarProvider>
-        <div />
-      </SidebarProvider>,
+    expect(primitiveSidebarWidths().expanded).toBe(CONSOLE_EXPANDED_SIDEBAR_WIDTH);
+  });
+
+  it('restates the drawer a list record opens in (plugin-view’s md bucket)', () => {
+    // `min(92vw, 720px)`: the px term is the drawer's width on any window the fold applies to.
+    const match = /^min\(92vw, (\d+)px\)$/.exec(overlayWidthFor('md', {}));
+    expect(match, 'overlayWidthFor answers min(92vw, Npx)').not.toBeNull();
+    expect(Number(match![1])).toBe(RECORD_DRAWER_WIDTH);
+  });
+
+  it('is the drawer beside the narrowest list that draws its columns, plus the expanded sidebar', () => {
+    expect(RECORD_DRAWER_MIN_CONTENT_WIDTH).toBe(LIST_MIN_COLUMNS_WIDTH + RECORD_DRAWER_WIDTH);
+    expect(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH).toBe(RECORD_DRAWER_MIN_CONTENT_WIDTH + CONSOLE_EXPANDED_SIDEBAR_WIDTH);
+    // The value the maintainer kept when the split pane retired: 440 + 720 + 256.
+    expect(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH).toBe(1416);
+    // At the threshold the expanded sidebar leaves exactly the list's floor beside the drawer.
+    expect(listBesideDrawer(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH, CONSOLE_EXPANDED_SIDEBAR_WIDTH)).toBe(
+      LIST_MIN_COLUMNS_WIDTH,
     );
-    const wrapper = container.firstElementChild as HTMLElement;
-    const primitiveWidth = wrapper.style.getPropertyValue('--sidebar-width');
-    expect(toPx(primitiveWidth)).toBe(CONSOLE_EXPANDED_SIDEBAR_WIDTH);
   });
 
-  it('is the split’s content beside the expanded sidebar', () => {
-    expect(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH).toBe(RECORD_SPLIT_MIN_CONTENT_WIDTH + CONSOLE_EXPANDED_SIDEBAR_WIDTH);
+  it('folds a 1280 px and a 1366 px window, whose rail leaves the list its columns beside the drawer', () => {
+    const { expanded, rail } = primitiveSidebarWidths();
+    for (const width of [1280, 1366]) {
+      expect(width).toBeLessThan(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH);
+      expect(listBesideDrawer(width, expanded)).toBeLessThan(LIST_MIN_COLUMNS_WIDTH);
+      expect(listBesideDrawer(width, rail)).toBeGreaterThanOrEqual(LIST_MIN_COLUMNS_WIDTH);
+    }
   });
 
-  it('folds a 1280 px window and leaves a 1440 px one alone, as the card accepts', () => {
-    expect(1280).toBeLessThan(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH);
+  it('leaves a 1440 px window’s sidebar expanded', () => {
     expect(1440).toBeGreaterThanOrEqual(CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH);
+    expect(listBesideDrawer(1440, CONSOLE_EXPANDED_SIDEBAR_WIDTH)).toBeGreaterThanOrEqual(LIST_MIN_COLUMNS_WIDTH);
   });
 });
@@ -4,9 +4,10 @@
  * consoleSidebarRail — when the console sidebar folds to its icon rail on its
  * own, and the reader's override (objectstack#27593).
  *
- * On a window too narrow for the record split beside an expanded sidebar the
- * sidebar mounts as the icon rail, and a click on the rail (or the app bar's
- * trigger, or ⌘B) expands it OVER the content instead of beside it. A reader
+ * On a window too narrow for the record drawer and the list beside it next to
+ * an expanded sidebar, the sidebar mounts as the icon rail, and a click on the
+ * rail (or the app bar's trigger, or ⌘B) expands it OVER the content instead
+ * of beside it. A reader
  * who keeps it open ({@link CONSOLE_SIDEBAR_KEEP_OPEN_PREFERENCE}) gets the
  * wide-window behaviour at every width above the phone breakpoint, where the
  * primitive's drawer takes over.
@@ -36,23 +37,42 @@ import {
 export const CONSOLE_EXPANDED_SIDEBAR_WIDTH = 256;
 
 /**
- * The content width the record split needs to draw its list's columns: the
- * narrowest list that still draws them (440) beside the record pane at its
- * default width (720), objectstack#27545.
+ * The record drawer's width in CSS pixels: a list record opens in the drawer
+ * at plugin-view's `md` overlay bucket, `overlayWidthFor('md', …)` =
+ * `min(92vw, 720px)` (objectstack#27545). `consoleSidebarRail.width-27593.test.tsx`
+ * reads that value and holds this equal to it, so the derived threshold below
+ * follows the drawer.
  */
-export const RECORD_SPLIT_MIN_CONTENT_WIDTH = 440 + 720;
+export const RECORD_DRAWER_WIDTH = 720;
+
+/**
+ * The narrowest list that still draws its columns, in CSS pixels: the 440 px
+ * measured on objectstack#27545. The drawer is non-modal over a list and draws
+ * no dimming there, so the list beside it stays readable and a click on
+ * another row swaps the record (`NavigationOverlay` in `@object-ui/components`).
+ */
+export const LIST_MIN_COLUMNS_WIDTH = 440;
+
+/**
+ * The content width the record drawer needs over the full-width list: the
+ * drawer (720) and, beside it, the narrowest list that still draws its
+ * columns (440).
+ */
+export const RECORD_DRAWER_MIN_CONTENT_WIDTH = LIST_MIN_COLUMNS_WIDTH + RECORD_DRAWER_WIDTH;
 
 /**
  * Below this window width the sidebar folds to the icon rail on its own.
  *
- * Derived, not picked: a window narrower than the split's content plus the
- * expanded sidebar cannot fit the split beside the expanded sidebar, so the
- * sidebar gives the content its width. 1160 + 256 = 1416: a 1280 px window
- * folds (1280 − the 48 px rail leaves 1232 for the split), a 1440 px window
- * keeps the sidebar expanded (1184 left). The record page's own column tiers
- * are measured on the container it gets, so they follow either way.
+ * Derived, not picked: a window narrower than the drawer's content plus the
+ * expanded sidebar cannot keep the list's columns beside the open drawer with
+ * the sidebar expanded, so the sidebar gives the content its width.
+ * 1160 + 256 = 1416: a 1280 px window folds (1280 − the 48 px rail − the
+ * drawer leaves 512 px of list beside it, where the expanded sidebar would
+ * leave 304), a 1440 px window keeps the sidebar expanded (464 left). The
+ * record page's own column tiers are measured on the container it gets, so
+ * they follow either way.
  */
-export const CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH = RECORD_SPLIT_MIN_CONTENT_WIDTH + CONSOLE_EXPANDED_SIDEBAR_WIDTH;
+export const CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH = RECORD_DRAWER_MIN_CONTENT_WIDTH + CONSOLE_EXPANDED_SIDEBAR_WIDTH;
 
 /**
  * The reader's "keep the sidebar open": `on` turns the fold off, so a narrow
 
@@ -52,8 +52,13 @@
  * The console sidebar's width when it is expanded: `SIDEBAR_WIDTH` (16rem) of
  * the sidebar primitive in `@object-ui/components`. Measured on the console
  * (HotCRM contact record page, sidebar expanded, objectstack#27241): the
- * record page root is the window minus this — 1184 px in a 1440 px window,
- * 1024 px in 1280, 768 px in 1024.
+ * record page root is the window minus this — 1184 px in a 1440 px window.
+ * Below 1416 px the console folds the sidebar to its 48 px icon rail
+ * (`CONSOLE_SIDEBAR_RAIL_BELOW_WIDTH` in `@object-ui/app-shell`,
+ * objectstack#27593), so a 1280 px window gives the root 1232 px and a 1024 px
+ * one 976 px; only a reader who keeps the sidebar open gets 1024 px in 1280
+ * and 768 px in 1024. The floors below are derived for the expanded sidebar,
+ * so the rail only ever gives the page more room than they assume.
  */
 const EXPANDED_SIDEBAR_WIDTH = 256;