style(webui): float in conversation highlight

webui/src/components/ChatList.tsx

@@ -107,6 +107,8 @@ export const ChatList = memo(function ChatList({
   const listContentRef = useRef<HTMLDivElement>(null);
   const activeRowRef = useRef<HTMLDivElement>(null);
   const activeHighlightRef = useRef<HTMLDivElement>(null);
+  const activeHighlightSurfaceRef = useRef<HTMLDivElement>(null);
+  const highlightVisibleRef = useRef(false);
   const labels = useMemo<ChatGroupLabels>(() => ({
     pinned: t("chat.groups.pinned"),
     all: t("chat.groups.all"),
@@ -162,17 +164,27 @@ export const ChatList = memo(function ChatList({
   }, [showArchived, sort]);
 
   useLayoutEffect(() => {
+    let resetTransitionFrame: number | null = null;
+
     const updateHighlight = () => {
       const content = listContentRef.current;
       const row = activeRowRef.current;
       const highlight = activeHighlightRef.current;
+      const surface = activeHighlightSurfaceRef.current;
 
-      if (!highlight) return;
+      if (!highlight || !surface) return;
       if (!content || !row) {
-        highlight.style.opacity = "0";
+        surface.style.opacity = "0";
+        surface.style.transform = "scale(0.97)";
+        highlightVisibleRef.current = false;
         return;
       }
 
+      const shouldFloatIn = !highlightVisibleRef.current;
+      if (shouldFloatIn) {
+        highlight.style.transitionProperty = "none";
+      }
+
       const contentRect = content.getBoundingClientRect();
       const rowRect = row.getBoundingClientRect();
       highlight.style.width = `${rowRect.width}px`;
@@ -180,7 +192,21 @@ export const ChatList = memo(function ChatList({
       highlight.style.transform = `translate3d(${rowRect.left - contentRect.left}px, ${
         rowRect.top - contentRect.top
       }px, 0)`;
-      highlight.style.opacity = "1";
+
+      if (shouldFloatIn) {
+        void highlight.offsetWidth;
+      }
+
+      surface.style.opacity = "1";
+      surface.style.transform = "scale(1)";
+      highlightVisibleRef.current = true;
+
+      if (shouldFloatIn) {
+        resetTransitionFrame = window.requestAnimationFrame(() => {
+          highlight.style.removeProperty("transition-property");
+          resetTransitionFrame = null;
+        });
+      }
     };
 
     updateHighlight();
@@ -196,6 +222,10 @@ export const ChatList = memo(function ChatList({
     window.addEventListener("resize", updateHighlight);
 
     return () => {
+      if (resetTransitionFrame !== null) {
+        window.cancelAnimationFrame(resetTransitionFrame);
+      }
+      activeHighlightRef.current?.style.removeProperty("transition-property");
       resizeObserver?.disconnect();
       window.removeEventListener("resize", updateHighlight);
     };
@@ -449,10 +479,16 @@ export const ChatList = memo(function ChatList({
           ref={activeHighlightRef}
           data-testid="active-chat-highlight"
           aria-hidden="true"
-          className="pointer-events-none absolute left-0 top-0 z-0 !mt-0 rounded-xl bg-sidebar-foreground/[0.055] opacity-0 transition-[transform,width,height,opacity] duration-300 ease-out will-change-transform motion-reduce:transition-none dark:bg-white/[0.07]"
+          className="pointer-events-none absolute left-0 top-0 z-0 !mt-0 transition-[transform,width,height] duration-300 ease-out will-change-transform motion-reduce:transition-none"
+        >
+          <div
+            ref={activeHighlightSurfaceRef}
+            data-testid="active-chat-highlight-surface"
+            className="h-full w-full scale-[0.97] rounded-xl bg-sidebar-foreground/[0.055] opacity-0 transition-[opacity,transform] duration-200 ease-out motion-reduce:transition-none dark:bg-white/[0.07]"
           />
         </div>
       </div>
+    </div>
   );
 });
 

webui/src/tests/chat-list.test.tsx

@@ -220,7 +220,12 @@ describe("ChatList", () => {
     expect(within(chatsSection).queryByText("Project chat")).not.toBeInTheDocument();
   });
 
-  it("slides one borderless highlight between selected topics", () => {
+  it("floats a borderless highlight in, then slides it between selected topics", () => {
+    let revealFrame: FrameRequestCallback | null = null;
+    vi.spyOn(window, "requestAnimationFrame").mockImplementation((callback) => {
+      revealFrame = callback;
+      return 1;
+    });
     vi.spyOn(HTMLElement.prototype, "getBoundingClientRect").mockImplementation(
       function (this: HTMLElement) {
         if (this.hasAttribute("data-chat-list-content")) {
@@ -250,11 +255,26 @@ describe("ChatList", () => {
     const { rerender } = render(
       <ChatList
         {...props}
-        activeKey="websocket:active"
+        activeKey={null}
       />,
     );
 
     const highlight = screen.getByTestId("active-chat-highlight");
+    const surface = screen.getByTestId("active-chat-highlight-surface");
+    expect(surface).toHaveClass(
+      "bg-sidebar-foreground/[0.055]",
+      "transition-[opacity,transform]",
+      "motion-reduce:transition-none",
+    );
+    expect(surface).toHaveStyle("opacity: 0; transform: scale(0.97)");
+
+    rerender(
+      <ChatList
+        {...props}
+        activeKey="websocket:active"
+      />,
+    );
+
     const activeButton = screen.getByTitle("Active topic");
     expect(activeButton).toHaveAttribute("aria-current", "page");
     expect(activeButton.parentElement).not.toHaveClass(
@@ -262,13 +282,16 @@ describe("ChatList", () => {
       "shadow-[inset_0_0_0_1px_hsl(var(--sidebar-border)/0.55)]",
     );
     expect(highlight).toHaveClass(
-      "bg-sidebar-foreground/[0.055]",
+      "transition-[transform,width,height]",
-      "transition-[transform,width,height,opacity]",
       "motion-reduce:transition-none",
     );
     expect(highlight).toHaveStyle(
-      "width: 284px; height: 32px; transform: translate3d(8px, 12px, 0); opacity: 1",
+      "width: 284px; height: 32px; transform: translate3d(8px, 12px, 0); transition-property: none",
     );
+    expect(surface).toHaveStyle("opacity: 1; transform: scale(1)");
+
+    revealFrame?.(0);
+    expect(highlight.style.transitionProperty).toBe("");
 
     rerender(
       <ChatList
@@ -280,7 +303,7 @@ describe("ChatList", () => {
     expect(screen.getByTitle("Active topic")).not.toHaveAttribute("aria-current");
     expect(screen.getByTitle("Inactive topic")).toHaveAttribute("aria-current", "page");
     expect(highlight).toHaveStyle(
-      "width: 284px; height: 40px; transform: translate3d(8px, 48px, 0); opacity: 1",
+      "width: 284px; height: 40px; transform: translate3d(8px, 48px, 0)",
     );
   });