editor: resizable rail, Esc closes panel, dev tab remembered

Rail gets a drag handle on its edge (240-640px, width persisted like
the rest of the panel state). Escape now closes the panel as the last
step of its chain (dialog > inline > selection > panel). The dev panel
remembers its tab across reloads. Panel toggle button title notes the
Esc shortcut. Harness covers resize/persist, Esc-close and dev tab.

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

test/rail-sections.test.tsx

@@ -59,6 +59,61 @@ describe('rail sections', () => {
     expect(qa('.cms-outline').length).toBeGreaterThan(0)
   })
 
+  it('dragging the rail edge resizes it and remembers the width', async () => {
+    h = await setup()
+    await h.settle()
+    await h.press('Panel')
+    await h.settle()
+    const grip = q('.cms-rail__resize')
+    const down = new Event('pointerdown', { bubbles: true, cancelable: true }) as Event & { clientX: number; button: number }
+    down.clientX = 332
+    down.button = 0
+    await act(async () => void grip.dispatchEvent(down))
+    const move = new Event('pointermove', { bubbles: true, cancelable: true }) as Event & { clientX: number }
+    move.clientX = 420
+    await act(async () => void document.dispatchEvent(move))
+    const up = new Event('pointerup', { bubbles: true, cancelable: true })
+    await act(async () => void document.dispatchEvent(up))
+    await h.settle()
+    // jsdom reports rect.left as 0, so width == clientX, clamped to [240, 640]
+    expect((q('.cms-rail') as HTMLElement).style.width).toBe('420px')
+    expect(localStorage.getItem('cms-onpage.railwidth')).toBe('420')
+    h.cleanup()
+    h = await setup({ keepStorage: true })
+    await h.settle()
+    await h.settle()
+    expect((q('.cms-rail') as HTMLElement).style.width).toBe('420px')
+  })
+
+  it('Escape closes the rail when nothing else is open', async () => {
+    h = await setup()
+    await h.settle()
+    await h.press('Panel')
+    await h.settle()
+    expect(q('.cms-rail')).not.toBeNull()
+    await act(async () => void document.dispatchEvent(new KeyboardEvent('keydown', { key: 'Escape', bubbles: true, cancelable: true, composed: true })))
+    await h.settle()
+    expect(h.shadow.querySelector('.cms-rail')).toBeNull()
+    expect(localStorage.getItem('cms-onpage.rail')).toBe('false')
+  })
+
+  it('dev panel remembers its tab', async () => {
+    h = await setup()
+    await h.settle()
+    await act(async () => void h.editor.ctrl.store.set({ dev: true }))
+    await h.settle()
+    const registry = qa('.cms-dev header button').find((b) => b.textContent === 'registry')!
+    await act(async () => void registry.click())
+    await h.settle()
+    expect(localStorage.getItem('cms-onpage.devtab')).toBe('registry')
+    h.cleanup()
+    h = await setup({ keepStorage: true })
+    await h.settle()
+    await act(async () => void h.editor.ctrl.store.set({ dev: true }))
+    await h.settle()
+    expect(q('.cms-dev__body').textContent).toContain('blockEditors')
+  })
+
   it('assistant sits beside the dev panel instead of stacking under it', async () => {
     ;(navigator as any).gpu = {} // aiSupported() checks for a WebGPU API
     h = await setup()