fix(desktop): gate the HUD resize frame's hit test on engagement (#108793)

The resize frame was unconditionally pointer-events: auto, so a
collapsed HUD kept an invisible ring of window — nothing painted,
every click and drag aimed at the app underneath eaten. The frame now
rides the band's engagement gates: the caret in the composer
(data-hud-typing, stamped live by useHudGlass), a held band, or a
solid-input host re-arm it; an in-flight drag keeps its own handle
live via data-hud-grabbing (pointer capture routes the moves).

Direction from #108796 (liuhao1024); behavioral test instead of that
PR's source-reading one.

Co-authored-by: liuhao1024 <noreply@github.com>

apps/desktop/src/app/hud/resize-frame.test.tsx

@@ -0,0 +1,91 @@
+// @vitest-environment jsdom
+import { act, cleanup, render } from '@testing-library/react'
+import { MemoryRouter } from 'react-router'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+vi.mock('../contrib/wiring', () => ({ WiredPane: () => null }))
+
+class ResizeObserverStub {
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+}
+Object.assign(globalThis, { ResizeObserver: ResizeObserverStub })
+
+import { HudShell } from './hud-shell'
+
+/** #108793: the resize frame's hit-testability rides the shell's engagement
+ * gates (styles.css keys `pointer-events` off them). The contract under test:
+ * an idle HUD carries NONE of the gates, so the invisible frame falls out of
+ * the hit test entirely; each arm — caret in the composer, a held band, a
+ * solid-input host — re-arms it on its own. */
+describe('HudShell resize-frame engagement gates', () => {
+  afterEach(() => {
+    cleanup()
+    vi.restoreAllMocks()
+    delete (window as { hermesDesktop?: unknown }).hermesDesktop
+  })
+
+  const shellOf = (container: HTMLElement) => {
+    const shell = container.querySelector('[data-hud-shell]')
+
+    expect(shell).not.toBeNull()
+
+    return shell as HTMLElement
+  }
+
+  it('an idle HUD carries none of the engagement gates the frame keys on', () => {
+    const { container } = render(
+      <MemoryRouter>
+        <HudShell />
+      </MemoryRouter>
+    )
+    const shell = shellOf(container)
+
+    expect(shell.hasAttribute('data-hud-typing')).toBe(false)
+    expect(shell.hasAttribute('data-hud-held')).toBe(false)
+    expect(shell.getAttribute('data-hud-input')).toBe('click-through')
+    // The frame itself is mounted (the resize grammar is not conditional) but
+    // no handle is mid-drag.
+    const handles = shell.querySelectorAll('[data-hud-resize]')
+
+    expect(handles.length).toBeGreaterThan(0)
+    handles.forEach(handle => {
+      expect(handle.hasAttribute('data-hud-grabbing')).toBe(false)
+    })
+  })
+
+  it('focus in the composer arms the typing gate the frame re-arms on', () => {
+    const { container } = render(
+      <MemoryRouter>
+        <HudShell />
+      </MemoryRouter>
+    )
+    const shell = shellOf(container)
+
+    // useHudGlass stamps data-hud-typing live from the :focus query — the
+    // same gate the frost and the scrim run on.
+    const composer = document.createElement('input')
+
+    composer.setAttribute('data-slot', 'composer-rich-input')
+    act(() => {
+      shell.appendChild(composer)
+      composer.focus()
+      composer.dispatchEvent(new FocusEvent('focusin', { bubbles: true }))
+    })
+
+    expect(shell.hasAttribute('data-hud-typing')).toBe(true)
+  })
+
+  it('a solid-input host keeps the frame live unconditionally', () => {
+    Object.assign(window, { hermesDesktop: { hud: { windowing: { solid: true } } } })
+
+    const { container } = render(
+      <MemoryRouter>
+        <HudShell />
+      </MemoryRouter>
+    )
+
+    expect(shellOf(container).getAttribute('data-hud-input')).toBe('solid')
+  })
+})

apps/desktop/src/styles.css

@@ -3578,14 +3578,33 @@ button[data-slot='aui_msg-reactions'] svg {
 
    CanvasTTY grammar: four edge strips + four larger corner targets, each with
    its native resize cursor and each preserving the opposite edge. Deliberately
-   invisible chrome: no glyph or border over whatever app is below the HUD. */
+   invisible chrome: no glyph or border over whatever app is below the HUD.
+
+   Invisible chrome that is ALWAYS hit-testable is a dead zone: an idle HUD is
+   just the bar, the window hands every other point to the app underneath, and
+   the only thing left answering the cursor was this frame — a thin invisible
+   ring that swallowed clicks and drags aimed at the app behind it (#108793).
+   So the frame rides the band's engagement gates: while the HUD is being used
+   (caret in the composer — data-hud-typing, stamped live by useHudGlass — or a
+   held band waiting on an answer) its edges may be grabbed; an in-flight
+   resize keeps its own handle live via data-hud-grabbing, because pointer
+   capture routes the moves to the handle that started the drag. Solid-input
+   hosts (X11) never hand the window away in the first place, so their frame
+   stays live unconditionally. */
 [data-hud-shell] [data-hud-resize] {
   position: absolute;
   z-index: 20;
-  pointer-events: auto;
+  pointer-events: none;
   touch-action: none;
 }
 
+[data-hud-shell][data-hud-typing] [data-hud-resize],
+[data-hud-shell][data-hud-held] [data-hud-resize],
+[data-hud-shell][data-hud-input='solid'] [data-hud-resize],
+[data-hud-shell] [data-hud-resize][data-hud-grabbing] {
+  pointer-events: auto;
+}
+
 [data-hud-shell] [data-hud-resize='n'] {
   top: 0;
   right: 1.25rem;