fix: keep assistant menu selection visible

apps/nextjs/src/components/assistant/assistant-trigger-scroll.spec.ts

@@ -0,0 +1,53 @@
+import { describe, expect, test } from "vitest";
+
+import { getNearestTriggerScrollTop } from "./assistant-trigger-scroll";
+
+describe("getNearestTriggerScrollTop", () => {
+  test("keeps a fully visible highlighted item in place", () => {
+    expect(
+      getNearestTriggerScrollTop({
+        scrollTop: 120,
+        viewportTop: 100,
+        viewportBottom: 400,
+        itemTop: 180,
+        itemBottom: 228,
+      }),
+    ).toBe(120);
+  });
+
+  test("scrolls down only enough to reveal the highlighted item", () => {
+    expect(
+      getNearestTriggerScrollTop({
+        scrollTop: 120,
+        viewportTop: 100,
+        viewportBottom: 400,
+        itemTop: 388,
+        itemBottom: 436,
+      }),
+    ).toBe(156);
+  });
+
+  test("scrolls up only enough to reveal the highlighted item", () => {
+    expect(
+      getNearestTriggerScrollTop({
+        scrollTop: 120,
+        viewportTop: 100,
+        viewportBottom: 400,
+        itemTop: 72,
+        itemBottom: 120,
+      }),
+    ).toBe(92);
+  });
+
+  test("clamps upward scrolling at the start of the list", () => {
+    expect(
+      getNearestTriggerScrollTop({
+        scrollTop: 12,
+        viewportTop: 100,
+        viewportBottom: 400,
+        itemTop: 40,
+        itemBottom: 88,
+      }),
+    ).toBe(0);
+  });
+});