test: target terminal viewport for scroll perf probe

tests/e2e/artificial-opencode-scroll-scenario.ts

@@ -82,12 +82,17 @@ export async function measureActiveTerminalWheelScroll(page: Page): Promise<Scro
     })()
     pane.terminal.focus()
     pane.terminal.scrollToBottom()
-    const screen = pane.container.querySelector<HTMLElement>('.xterm-screen')
-    if (!screen) {
-      throw new Error('Active terminal screen is unavailable')
+    // Why: Linux headless can miss wheel input over xterm's text layer while
+    // output is flooding; the viewport is the scrollable surface users affect.
+    const wheelTarget =
+      pane.container.querySelector<HTMLElement>('.xterm-viewport') ??
+      pane.container.querySelector<HTMLElement>('.xterm') ??
+      pane.container.querySelector<HTMLElement>('.xterm-screen')
+    if (!wheelTarget) {
+      throw new Error('Active terminal wheel target is unavailable')
     }
     const buffer = pane.terminal.buffer.active
-    const rect = screen.getBoundingClientRect()
+    const rect = wheelTarget.getBoundingClientRect()
     return {
       baseY: buffer.baseY,
       beforeViewportY: buffer.viewportY,
@@ -119,6 +124,16 @@ export async function measureActiveTerminalWheelScroll(page: Page): Promise<Scro
   await page.mouse.move(target.x, target.y)
   await page.mouse.wheel(0, -1200)
   let afterViewportY = target.beforeViewportY
+  while (performance.now() - start < 75) {
+    afterViewportY = await readActiveTerminalViewportY(page)
+    if (afterViewportY < target.beforeViewportY) {
+      break
+    }
+    await page.waitForTimeout(5)
+  }
+  if (afterViewportY >= target.beforeViewportY) {
+    await dispatchActiveTerminalWheelEvent(page)
+  }
   while (performance.now() - start < 500) {
     afterViewportY = await readActiveTerminalViewportY(page)
     if (afterViewportY < target.beforeViewportY) {
@@ -164,6 +179,45 @@ export function annotateScrollMeasurement(
   })
 }
 
+async function dispatchActiveTerminalWheelEvent(page: Page): Promise<void> {
+  await page.evaluate(() => {
+    const store = window.__store
+    const state = store?.getState()
+    const worktreeId = state?.activeWorktreeId
+    const tabId =
+      state?.activeTabType === 'terminal'
+        ? state.activeTabId
+        : worktreeId
+          ? (state?.activeTabIdByWorktree?.[worktreeId] ?? null)
+          : null
+    const manager = tabId ? window.__paneManagers?.get(tabId) : null
+    const pane = manager?.getActivePane?.() ?? manager?.getPanes?.()[0] ?? null
+    if (!pane) {
+      throw new Error('Active terminal pane is unavailable')
+    }
+    // Why: CI can drop CDP wheel input while the active textarea is focused;
+    // dispatching on xterm's own surfaces still exercises its user scroll path.
+    const wheelTargets = [
+      pane.container.querySelector<HTMLElement>('.xterm'),
+      pane.container.querySelector<HTMLElement>('.xterm-viewport'),
+      pane.container.querySelector<HTMLElement>('.xterm-screen')
+    ].filter((target): target is HTMLElement => Boolean(target))
+    if (wheelTargets.length === 0) {
+      throw new Error('Active terminal wheel target is unavailable')
+    }
+    for (const wheelTarget of wheelTargets) {
+      wheelTarget.dispatchEvent(
+        new WheelEvent('wheel', {
+          bubbles: true,
+          cancelable: true,
+          deltaMode: WheelEvent.DOM_DELTA_PIXEL,
+          deltaY: -1200
+        })
+      )
+    }
+  })
+}
+
 async function readActiveTerminalViewportY(page: Page): Promise<number> {
   return page.evaluate(() => {
     const store = window.__store