fix(tui): flash tabs on prompt admission (#39702)

packages/tui/test/component/tab-pulse.test.tsx

@@ -1,6 +1,10 @@
+/** @jsxImportSource @opentui/solid */
 import { expect, test } from "bun:test"
 import { RGBA } from "@opentui/core"
+import { testRender } from "@opentui/solid"
+import { createSignal } from "solid-js"
 import {
+  TabPulse,
   blendTabPulseColor,
   completionPulseOpacity,
   glowIgnitionLevel,
@@ -8,6 +12,50 @@ import {
 } from "../../src/component/tab-pulse"
 import { tint } from "../../src/theme/color"
 
+test("a prompt pulse restarts the neutral edge flash while the tab remains busy", async () => {
+  const background = RGBA.fromHex("#101010")
+  const flash = RGBA.fromHex("#f0f0f0")
+  const [promptPulse, setPromptPulse] = createSignal(0)
+  const app = await testRender(
+    () => (
+      <box width={8} height={1} backgroundColor={background}>
+        <TabPulse
+          active={true}
+          promptPulse={promptPulse()}
+          color={background}
+          flashColor={flash}
+          backgroundColor={background}
+        />
+      </box>
+    ),
+    { width: 8, height: 1 },
+  )
+
+  const firstBackground = () => app.captureSpans().lines[0]?.spans[0]?.bg
+
+  try {
+    await app.renderOnce()
+    expect(firstBackground()?.equals(background)).toBeTrue()
+
+    setPromptPulse(1)
+    await Bun.sleep(80)
+    await app.renderOnce()
+    expect(firstBackground()?.equals(background)).toBeFalse()
+    expect(firstBackground()?.r ?? 0).toBeGreaterThan(0.17)
+
+    await Bun.sleep(800)
+    await app.renderOnce()
+    expect(firstBackground()?.equals(background)).toBeTrue()
+
+    setPromptPulse(2)
+    await Bun.sleep(80)
+    await app.renderOnce()
+    expect(firstBackground()?.equals(background)).toBeFalse()
+  } finally {
+    app.renderer.destroy()
+  }
+})
+
 test("completion pulse rises quickly and fades over the remaining duration", () => {
   expect(completionPulseOpacity(0)).toBe(0)
   expect(completionPulseOpacity(0.06)).toBeCloseTo(0.5)