From ddf982332ccae1fb71344304de4b3bdcbe46faa6 Mon Sep 17 00:00:00 2001
From: Cheng Peng <cheng@block.xyz>
Date: Tue, 3 Nov 2026 22:57:36 -0800
Subject: [PATCH 1/2] fix(messages): pick the latest message with the shared
 ordering

The newest-message lookup behind Up-to-edit and react-to-latest compared
whole-second createdAt and kept the first row on a tie, so in a
same-second burst it picked an earlier message. Use compareMessages, the
rendered order (send ms, then id).

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Cheng Peng <cheng@block.xyz>
Co-authored-by: Cursor <cursoragent@cursor.com>
---
 .../messages/use-message-selection.test.tsx   | 52 +++++++++++++++++++
 .../messages/use-message-selection.ts         |  3 +-
 2 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 src/features/messages/use-message-selection.test.tsx

diff --git a/src/features/messages/use-message-selection.test.tsx b/src/features/messages/use-message-selection.test.tsx
new file mode 100644
index 0000000000..c8b99a1ea5
--- /dev/null
+++ b/src/features/messages/use-message-selection.test.tsx
@@ -0,0 +1,52 @@
+// @vitest-environment jsdom
+import { cleanup, render } from "@testing-library/react";
+import { useRef } from "react";
+import { afterEach, expect, it } from "vitest";
+import type { ChannelMessage } from "../relay/contracts";
+import type { RelaySession } from "../relay/session";
+import { selectNewestMessage } from "./message-selection";
+import { useMessageSelection } from "./use-message-selection";
+
+afterEach(cleanup);
+
+const message = (id: string, createdAt: number, createdAtMs?: number) =>
+  ({ id, createdAt, createdAtMs }) as ChannelMessage;
+
+function List({ rows }: { rows: readonly ChannelMessage[] }) {
+  const list = useRef<HTMLElement>(null);
+  useMessageSelection(list, rows, {} as RelaySession);
+  return (
+    <section ref={list} data-testid="list">
+      {rows.map((row) => (
+        <div key={row.id} data-message-id={row.id}>
+          <div data-layout="timeline">{row.id}</div>
+        </div>
+      ))}
+    </section>
+  );
+}
+
+function newestSelected(rows: readonly ChannelMessage[]) {
+  const { getByTestId } = render(<List rows={rows} />);
+  expect(selectNewestMessage(getByTestId("list"))).toBe(true);
+  return document.activeElement?.closest<HTMLElement>("[data-message-id]")
+    ?.dataset.messageId;
+}
+
+it("selects the latest message of a same-second burst by send ms, then id", () => {
+  expect(
+    newestSelected([message("z", 100, 100_100), message("a", 100, 100_200)]),
+  ).toBe("a");
+  cleanup();
+  expect(newestSelected([message("a", 100), message("b", 100)])).toBe("b");
+});
+
+it("selects the latest message across seconds and skips membership notices", () => {
+  const notice = {
+    ...message("notice", 300),
+    membership: {},
+  } as ChannelMessage;
+  expect(
+    newestSelected([message("old", 100), message("new", 200), notice]),
+  ).toBe("new");
+});
diff --git a/src/features/messages/use-message-selection.ts b/src/features/messages/use-message-selection.ts
index f39a4ed060..b0bb1a1476 100644
--- a/src/features/messages/use-message-selection.ts
+++ b/src/features/messages/use-message-selection.ts
@@ -1,5 +1,6 @@
 import { useLayoutEffect, useRef, type RefObject } from "react";
 import type { ChannelMessage } from "../relay/contracts";
+import { compareMessages } from "../relay/message-order";
 import type { RelaySession } from "../relay/session";
 import { useMessageEditScope } from "./MessageEditScope";
 import { useMessageKeyActions } from "./MessageManagement";
@@ -26,7 +27,7 @@ export function useMessageSelection(
       newest: () =>
         latest.current.reduce<ChannelMessage | undefined>(
           (newest, row) =>
-            !row.membership && (!newest || row.createdAt > newest.createdAt)
+            !row.membership && (!newest || compareMessages(row, newest) > 0)
               ? row
               : newest,
           undefined,

From 3695aeec0b51cde781ecf8fcc8383424d959c156 Mon Sep 17 00:00:00 2001
From: Cheng Peng <cheng@block.xyz>
Date: Tue, 3 Nov 2026 23:19:28 -0800
Subject: [PATCH 2/2] test(messages): mount the newest-message test in
 StrictMode

Follow the mounted-test conventions in docs/contributing.md: render with
reactStrictMode and find the list by its region role instead of a test id.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>
Signed-off-by: Cheng Peng <cheng@block.xyz>
---
 src/features/messages/use-message-selection.test.tsx | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/features/messages/use-message-selection.test.tsx b/src/features/messages/use-message-selection.test.tsx
index c8b99a1ea5..b9dc681666 100644
--- a/src/features/messages/use-message-selection.test.tsx
+++ b/src/features/messages/use-message-selection.test.tsx
@@ -16,7 +16,7 @@ function List({ rows }: { rows: readonly ChannelMessage[] }) {
   const list = useRef<HTMLElement>(null);
   useMessageSelection(list, rows, {} as RelaySession);
   return (
-    <section ref={list} data-testid="list">
+    <section ref={list} aria-label="Messages">
       {rows.map((row) => (
         <div key={row.id} data-message-id={row.id}>
           <div data-layout="timeline">{row.id}</div>
@@ -27,8 +27,10 @@ function List({ rows }: { rows: readonly ChannelMessage[] }) {
 }
 
 function newestSelected(rows: readonly ChannelMessage[]) {
-  const { getByTestId } = render(<List rows={rows} />);
-  expect(selectNewestMessage(getByTestId("list"))).toBe(true);
+  const { getByRole } = render(<List rows={rows} />, { reactStrictMode: true });
+  expect(selectNewestMessage(getByRole("region", { name: "Messages" }))).toBe(
+    true,
+  );
   return document.activeElement?.closest<HTMLElement>("[data-message-id]")
     ?.dataset.messageId;
 }