fix(tui): keep streaming progress stable during interaction

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

@@ -0,0 +1,28 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+
+import { getInteractionMode, markScrolling, markTyping, resetInteractionMode } from '../app/interactionMode.js'
+import { SCROLLING_IDLE_MS, TYPING_IDLE_MS } from '../config/timing.js'
+
+describe('interactionMode', () => {
+  afterEach(() => {
+    resetInteractionMode()
+    vi.useRealTimers()
+  })
+
+  it('holds scrolling mode briefly then returns idle', () => {
+    vi.useFakeTimers()
+    markScrolling()
+    expect(getInteractionMode()).toBe('scrolling')
+    vi.advanceTimersByTime(SCROLLING_IDLE_MS)
+    expect(getInteractionMode()).toBe('idle')
+  })
+
+  it('typing takes priority over scrolling', () => {
+    vi.useFakeTimers()
+    markTyping()
+    markScrolling()
+    expect(getInteractionMode()).toBe('typing')
+    vi.advanceTimersByTime(TYPING_IDLE_MS)
+    expect(getInteractionMode()).toBe('idle')
+  })
+})