Ensure sent markers are hidden when showing thread summary. (#31076)

* Ensure read markers are hidden when showing thread summary.

* lint

* update screenshot

Author: Half-Shot

playwright/e2e/threads/threads.spec.ts

@@ -445,7 +445,7 @@ test.describe("Threads", () => {
         await expect(locator.locator(".mx_EventTile").last().getByText("Hello Mr. User")).toBeAttached();
     });
 
-    test("navigate through right panel", async ({ page, app, user }) => {
+    test("navigate through right panel", { tag: "@screenshot" }, async ({ page, app, user }) => {
         // Create room
         const roomId = await app.client.createRoom({});
         await page.goto("/#/room/" + roomId);
@@ -497,6 +497,9 @@ test.describe("Threads", () => {
         await expect(
             threadPanel.locator(".mx_EventTile_last").getByText("Hello again Mr. User in a thread"),
         ).toBeVisible();
+        await expect(threadPanel).toMatchScreenshot("thread-panel.png", {
+            css: ".mx_MessageTimestamp { visibility: hidden !important; }",
+        });
 
         const rightPanel = page.locator(".mx_RightPanel");
         // Check that the threads are listed

playwright/snapshots/threads/threads.spec.ts/thread-panel-linux.png

@@ -360,6 +360,9 @@ export class UnwrappedEventTile extends React.Component<EventTileProps, IState>
         // We only show the 'sent' receipt on the last successful event.
         if (!this.props.lastSuccessful) return false;
 
+        // Don't show this in the thread view as it conflicts with the thread counter.
+        if (this.context.timelineRenderingType === TimelineRenderingType.ThreadsList) return false;
+
         // Check to make sure the sending state is appropriate. A null/undefined send status means
         // that the message is 'sent', so we're just double checking that it's explicitly not sent.
         if (this.props.eventSendStatus && this.props.eventSendStatus !== EventStatus.SENT) return false;