fix(tui): keep streaming progress stable during interaction

ui-tui/src/__tests__/virtualHistoryClamp.test.ts

@@ -0,0 +1,13 @@
+import { describe, expect, it } from 'vitest'
+
+import { shouldSetVirtualClamp } from '../hooks/useVirtualHistory.js'
+
+describe('virtual history clamp bounds', () => {
+  it('does not clamp sticky live tail content', () => {
+    expect(shouldSetVirtualClamp({ itemCount: 20, sticky: true, viewportHeight: 10 })).toBe(false)
+  })
+
+  it('sets clamp bounds after manual scroll breaks sticky mode', () => {
+    expect(shouldSetVirtualClamp({ itemCount: 20, sticky: false, viewportHeight: 10 })).toBe(true)
+  })
+})