fix(tui): refresh scroll height at cached bottom

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

@@ -3,9 +3,12 @@ import { describe, expect, it, vi } from 'vitest'
 import { scrollWithSelectionBy } from '../app/scroll.js'
 
 function makeScroll(overrides: Partial<Record<string, unknown>> = {}) {
+  const getScrollHeight = (overrides.getScrollHeight as (() => number) | undefined) ?? vi.fn(() => 100)
+
   return {
+    getFreshScrollHeight: vi.fn(() => getScrollHeight()),
     getPendingDelta: vi.fn(() => 0),
-    getScrollHeight: vi.fn(() => 100),
+    getScrollHeight,
     getScrollTop: vi.fn(() => 10),
     getViewportHeight: vi.fn(() => 20),
     getViewportTop: vi.fn(() => 0),
@@ -34,6 +37,47 @@ describe('scrollWithSelectionBy', () => {
     expect(s.scrollBy).toHaveBeenCalledWith(1)
   })
 
+  it('uses fresh scroll height when cached height would swallow a down-scroll at a fake bottom', () => {
+    const s = makeScroll({
+      getFreshScrollHeight: vi.fn(() => 34),
+      getScrollHeight: vi.fn(() => 30),
+      getScrollTop: vi.fn(() => 10),
+      getViewportHeight: vi.fn(() => 20)
+    })
+
+    const selection = {
+      captureScrolledRows: vi.fn(),
+      getState: vi.fn(() => null),
+      shiftAnchor: vi.fn(),
+      shiftSelection: vi.fn()
+    }
+
+    scrollWithSelectionBy(10, { scrollRef: { current: s as never }, selection })
+
+    expect(s.scrollBy).toHaveBeenCalledWith(4)
+  })
+
+  it('uses fresh height when pending down-scroll reaches the cached fake bottom', () => {
+    const s = makeScroll({
+      getFreshScrollHeight: vi.fn(() => 38),
+      getPendingDelta: vi.fn(() => 2),
+      getScrollHeight: vi.fn(() => 32),
+      getScrollTop: vi.fn(() => 10),
+      getViewportHeight: vi.fn(() => 20)
+    })
+
+    const selection = {
+      captureScrolledRows: vi.fn(),
+      getState: vi.fn(() => null),
+      shiftAnchor: vi.fn(),
+      shiftSelection: vi.fn()
+    }
+
+    scrollWithSelectionBy(10, { scrollRef: { current: s as never }, selection })
+
+    expect(s.scrollBy).toHaveBeenCalledWith(6)
+  })
+
   it('does nothing at the edge instead of queueing dead pending deltas', () => {
     const s = makeScroll({
       getScrollHeight: vi.fn(() => 30),

ui-tui/src/app/scroll.ts

@@ -13,6 +13,23 @@ export interface ScrollWithSelectionOptions {
   readonly selection: SelectionApi
 }
 
+function scrollBoundsForDelta(s: ScrollBoxHandle, cur: number, delta: number) {
+  const viewport = Math.max(0, s.getViewportHeight())
+  const cachedHeight = Math.max(viewport, s.getScrollHeight())
+  let max = Math.max(0, cachedHeight - viewport)
+
+  // getScrollHeight() is render-time cached. After the streaming tail is
+  // committed into virtual history, the Yoga height can be fresher than the
+  // cached value; if we clamp only against the cached fake bottom, wheel-down
+  // becomes a no-op and no render is scheduled to reveal the real tail.
+  if (delta > 0 && cur + delta >= max - 1) {
+    const freshHeight = Math.max(viewport, s.getFreshScrollHeight())
+    max = Math.max(0, freshHeight - viewport)
+  }
+
+  return { max, viewport }
+}
+
 export function scrollWithSelectionBy(delta: number, { scrollRef, selection }: ScrollWithSelectionOptions): void {
   const s = scrollRef.current
 
@@ -21,8 +38,7 @@ export function scrollWithSelectionBy(delta: number, { scrollRef, selection }: S
   }
 
   const cur = s.getScrollTop() + s.getPendingDelta()
-  const viewport = Math.max(0, s.getViewportHeight())
+  const { max, viewport } = scrollBoundsForDelta(s, cur, delta)
-  const max = Math.max(0, s.getScrollHeight() - viewport)
   const actual = Math.max(0, Math.min(max, cur + delta)) - cur
 
   if (actual === 0) {