fix(desktop): retain live rows after window exhaustion

desktop/src/features/messages/lib/channelWindowStore.test.mjs

@@ -154,14 +154,38 @@ test("live backdated rows stay outside pages and render in order", () => {
   );
 });
 
-test("live rows below the oldest retained boundary wait for paging", () => {
+test("live rows below an open oldest boundary wait for paging", () => {
   const store = replaceNewestChannelWindow(
     emptyChannelWindowStore(),
     page(null, [event("n", 110), event("a", 100)]),
   );
   assert.equal(mergeLiveChannelWindowEvent(store, event("old", 90)), store);
 });
 
+test("same-second live rows enter an exhausted short window regardless of id order", () => {
+  const store = replaceNewestChannelWindow(
+    emptyChannelWindowStore(),
+    page(null, [event("a", 100), event("m", 100)], { hasMore: false }),
+  );
+  const live = event("z", 100);
+  const withLive = mergeLiveChannelWindowEvent(store, live);
+
+  assert.notEqual(withLive, store);
+  assert.deepEqual(
+    flattenChannelWindowEvents(withLive).map((item) => item.content),
+    ["z", "m", "a"],
+  );
+});
+
+test("older live rows stay below an exhausted window", () => {
+  const store = replaceNewestChannelWindow(
+    emptyChannelWindowStore(),
+    page(null, [event("a", 100)], { hasMore: false }),
+  );
+
+  assert.equal(mergeLiveChannelWindowEvent(store, event("old", 99)), store);
+});
+
 test("live aux stays separate from authoritative page closure", () => {
   const store = replaceNewestChannelWindow(
     emptyChannelWindowStore(),

desktop/src/features/messages/lib/channelWindowStore.ts

@@ -178,7 +178,7 @@ export function mergeLiveThreadSummary(
 
 /**
  * Merge a live top-level event without mutating authoritative page boundaries.
- * Events below the oldest loaded boundary wait for ordinary relay pagination.
+ * Events below an open oldest boundary wait for ordinary relay pagination.
  */
 export function mergeLiveChannelWindowEvent(
   current: ChannelWindowStore,
@@ -205,7 +205,13 @@ export function mergeLiveChannelWindowEvent(
   }
   const oldestPage = current.pages[current.pages.length - 1];
   const oldest = oldestPage?.rows[oldestPage.rows.length - 1]?.event;
-  if (oldest && compareRelayOrder(event, oldest) >= 0) return current;
+  if (
+    oldest &&
+    (event.created_at < oldest.created_at ||
+      (oldestPage.hasMore && compareRelayOrder(event, oldest) >= 0))
+  ) {
+    return current;
+  }
   return {
     ...current,
     liveOverlay: current.liveOverlay