fix(chat): keep sent messages in view

src/app/chat/components/__tests__/chat-area-scroll.test.tsx

@@ -145,6 +145,51 @@ describe("ChatArea scrolling", () => {
     expect(scrollNode.scrollTop).toBe(100);
   });
 
+  it("forces the latest user message into view after the keyboard resizes", () => {
+    scrollHeight = 1_000;
+    clientHeight = 300;
+    const history = [createMessage("history-1")];
+    renderChatArea(root, history, true, { scrollToBottomSignal: 0 });
+    const scrollNode = getScrollNode(container);
+
+    clientHeight = 200;
+    scrollNode.scrollTop = 700;
+    act(() => scrollNode.dispatchEvent(new Event("scroll", { bubbles: true })));
+
+    scrollHeight = 1_200;
+    renderChatArea(
+      root,
+      [...history, createUserMessage("sent-1")],
+      true,
+      { scrollToBottomSignal: 1 },
+    );
+
+    expect(scrollNode.scrollTop).toBe(1_000);
+  });
+
+  it("scrolls below a promotion after the user sends a message", () => {
+    scrollHeight = 1_000;
+    clientHeight = 300;
+    const history = [createMessage("history-1")];
+    const promotion = createMessage("promotion-1");
+    renderChatArea(root, [...history, promotion], true, {
+      scrollToBottomSignal: 0,
+    });
+    const scrollNode = getScrollNode(container);
+    scrollNode.scrollTop = 100;
+    act(() => scrollNode.dispatchEvent(new Event("scroll", { bubbles: true })));
+
+    scrollHeight = 1_500;
+    renderChatArea(
+      root,
+      [...history, createUserMessage("sent-1"), promotion],
+      true,
+      { scrollToBottomSignal: 1 },
+    );
+
+    expect(scrollNode.scrollTop).toBe(1_200);
+  });
+
   it("preserves the visible message after older history is prepended", () => {
     scrollHeight = 1_000;
     clientHeight = 300;
@@ -184,6 +229,7 @@ function renderChatArea(
     canLoadMoreHistory?: boolean;
     isLoadingMoreHistory?: boolean;
     onLoadMoreHistory?: () => void;
+    scrollToBottomSignal?: number;
   } = {},
 ): void {
   act(() => {
@@ -227,6 +273,15 @@ function createMessage(id: string): UiMessage {
   };
 }
 
+function createUserMessage(id: string): UiMessage {
+  return {
+    id,
+    content: `Message ${id}`,
+    isFromAI: false,
+    date: "2026-07-15",
+  };
+}
+
 function getScrollNode(container: HTMLElement): HTMLElement {
   const node = container.querySelector<HTMLElement>(
     '[aria-label="Chat messages"]',