test: account for alternateScreen flag in empty headless snapshot assertions

The alt-screen scrollback fix threads an alternateScreen flag through the
headless snapshot return type. Two sibling empty-buffer tests used exact
toEqual() assertions that did not include the new (legitimately false) key.
Update them to reflect the correct snapshot shape.

src/main/runtime/mobile-subscribe-integration.test.ts

@@ -227,7 +227,10 @@ describe('mobile subscribe integration', () => {
       cols: 90,
       rows: 30,
       seq: 17,
-      source: 'headless'
+      source: 'headless',
+      // Non-alt-screen buffer reports alternateScreen=false so the renderer
+      // keeps its destructive scrollback clear on restore.
+      alternateScreen: false
     })
     await expect(runtime.serializeTerminalBuffer('pty-empty')).resolves.toBeNull()
   })

src/main/runtime/orca-runtime.test.ts

@@ -5267,7 +5267,10 @@ describe('OrcaRuntimeService', () => {
       cols: 90,
       rows: 30,
       seq: 17,
-      source: 'headless'
+      source: 'headless',
+      // Non-alt-screen buffer reports alternateScreen=false so the renderer
+      // keeps its destructive scrollback clear on restore.
+      alternateScreen: false
     })
     expect(serializeBuffer).not.toHaveBeenCalled()
   })