diff --git a/ui/src/pages/chat/chat-thread.test.ts b/ui/src/pages/chat/chat-thread.test.ts
index 429218bfb1a7..32e1246d75a8 100644
--- a/ui/src/pages/chat/chat-thread.test.ts
+++ b/ui/src/pages/chat/chat-thread.test.ts
@@ -257,6 +257,124 @@ describe("collapseCompletedTurnWork", () => {
     expect(workGroups).toHaveLength(2);
     expect(new Set(workGroups.map((item) => item.key)).size).toBe(2);
   });
+
+  it("keeps a completed-work row keyed to its final reply as older work is prepended", () => {
+    resetChatThreadState();
+    const finalReply = {
+      __openclaw: { id: "final-reply", seq: 3 },
+      role: "assistant",
+      content: "Done.",
+      timestamp: 3_000,
+    };
+    const initial = collapsedItems({
+      messages: [toolResult("call-1", 2_000), finalReply],
+    });
+    const initialWork = requireWorkGroup(initial[0]);
+
+    const prepended = collapsedItems({
+      messages: [
+        {
+          __openclaw: { id: "older-commentary", seq: 1 },
+          role: "assistant",
+          content: "Checking.",
+          timestamp: 1_000,
+        },
+        toolResult("call-1", 2_000),
+        finalReply,
+      ],
+    });
+    const prependedWork = requireWorkGroup(prepended[0]);
+
+    expect(prependedWork.key).toBe(initialWork.key);
+    expect(prependedWork.durationMs).toBeGreaterThan(initialWork.durationMs ?? 0);
+  });
+});
+
+describe("buildCachedChatItems row identity", () => {
+  it("preserves a same-role group key as messages are prepended and appended", () => {
+    resetChatThreadState();
+    const first = {
+      __openclaw: { id: "assistant-1", seq: 2 },
+      role: "assistant",
+      content: "First",
+      timestamp: 2,
+    };
+    const second = {
+      __openclaw: { id: "assistant-2", seq: 3 },
+      role: "assistant",
+      content: "Second",
+      timestamp: 3,
+    };
+    const initial = groupAt(messageGroups({ messages: [first, second] }), 0);
+    const prepended = groupAt(
+      messageGroups({
+        messages: [
+          {
+            __openclaw: { id: "assistant-0", seq: 1 },
+            role: "assistant",
+            content: "Earlier",
+            timestamp: 1,
+          },
+          first,
+          second,
+        ],
+      }),
+      0,
+    );
+    const appended = groupAt(
+      messageGroups({
+        messages: [
+          ...prepended.messages.map((entry) => entry.message),
+          {
+            __openclaw: { id: "assistant-3", seq: 4 },
+            role: "assistant",
+            content: "Later",
+            timestamp: 4,
+          },
+        ],
+      }),
+      0,
+    );
+
+    expect(prepended.key).toBe(initial.key);
+    expect(appended.key).toBe(initial.key);
+  });
+
+  it("keeps a projected-sibling group stable after an unrelated prepend", () => {
+    resetChatThreadState();
+    const siblings = [
+      {
+        __openclaw: { id: "source-message", seq: 2 },
+        role: "assistant",
+        content: "First projection",
+        timestamp: 2,
+      },
+      {
+        __openclaw: { id: "source-message", seq: 2 },
+        role: "assistant",
+        content: "Second projection",
+        timestamp: 2,
+      },
+    ];
+    const initial = groupAt(messageGroups({ messages: siblings }), 0);
+    const prepended = groupAt(
+      messageGroups({
+        messages: [
+          {
+            __openclaw: { id: "older-user", seq: 1 },
+            role: "user",
+            content: "Earlier",
+            timestamp: 1,
+          },
+          ...siblings,
+        ],
+      }),
+      1,
+    );
+
+    expect(new Set(initial.messages.map((entry) => entry.key)).size).toBe(2);
+    expect(prepended.key).toBe(initial.key);
+  });
 });
 
 describe("buildCachedChatItems working spark", () => {
diff --git a/ui/src/pages/chat/chat-thread.ts b/ui/src/pages/chat/chat-thread.ts
index 8640fce2ce61..a2778bbee35f 100644
--- a/ui/src/pages/chat/chat-thread.ts
+++ b/ui/src/pages/chat/chat-thread.ts
@@ -1405,7 +1405,10 @@ function buildChatItems(props: BuildChatItemsProps): Array<ChatItem | MessageGro
           : liftedCanvasSource.timestamp;
       items.splice(insertionIndex, 0, {
         kind: "message",
-        key: `${messageKey(liftedCanvasSource.message, liftedCanvasSource.index + history.length)}:canvas`,
+        key: `${messageKey(
+          liftedCanvasSource.message,
+          liftedCanvasSource.index + history.length,
+        )}:canvas`,
         message: createCanvasAssistantMessage(liftedCanvasSource, timestamp),
       });
       continue;
@@ -1649,8 +1652,65 @@ function stabilizeChatItems(
   if (previous.length === 0 || next.length === 0) {
     return next;
   }
+  // Same-role groups can grow at either edge. Preserve the existing row key
+  // when loaded-history arrays retain message objects across prepend or append.
+  const previousGroupByMessage = new WeakMap<object, MessageGroup>();
+  const previousGroupByMessageKey = new Map<string, MessageGroup>();
+  for (const item of previous) {
+    if (item.kind !== "group") {
+      continue;
+    }
+    for (const message of item.messages) {
+      if (message.message && typeof message.message === "object") {
+        previousGroupByMessage.set(message.message, item);
+      }
+      previousGroupByMessageKey.set(message.key, item);
+    }
+  }
+  const claimedGroupKeys = new Set<string>();
+  const reconciled = next.map((item) => {
+    if (item.kind !== "group") {
+      return item;
+    }
+    const candidates = new Map<MessageGroup, { overlap: number; lastMatchIndex: number }>();
+    for (const [index, message] of item.messages.entries()) {
+      const prior =
+        message.message && typeof message.message === "object"
+          ? (previousGroupByMessage.get(message.message) ??
+            previousGroupByMessageKey.get(message.key))
+          : previousGroupByMessageKey.get(message.key);
+      if (
+        !prior ||
+        claimedGroupKeys.has(prior.key) ||
+        prior.role !== item.role ||
+        prior.senderLabel !== item.senderLabel
+      ) {
+        continue;
+      }
+      const candidate = candidates.get(prior);
+      candidates.set(prior, {
+        overlap: (candidate?.overlap ?? 0) + 1,
+        lastMatchIndex: index,
+      });
+    }
+    let best: { group: MessageGroup; overlap: number; lastMatchIndex: number } | null = null;
+    for (const [group, candidate] of candidates) {
+      if (
+        !best ||
+        candidate.overlap > best.overlap ||
+        (candidate.overlap === best.overlap && candidate.lastMatchIndex > best.lastMatchIndex)
+      ) {
+        best = { group, ...candidate };
+      }
+    }
+    if (!best) {
+      return item;
+    }
+    claimedGroupKeys.add(best.group.key);
+    return item.key === best.group.key ? item : { ...item, key: best.group.key };
+  });
   const previousByKey = new Map(previous.map((item) => [`${item.kind}\u0000${item.key}`, item]));
-  const stabilized = next.map((item) => {
+  const stabilized = reconciled.map((item) => {
     const prior = previousByKey.get(`${item.kind}\u0000${item.key}`);
     return prior && sameChatItem(prior, item) ? prior : item;
   });
@@ -1876,7 +1936,8 @@ export function collapseCompletedTurnWork(
     result.push(...turn.slice(0, segmentStart));
     result.push({
       kind: "work-group",
-      key: `work:${firstGroup.key}`,
+      // The final reply survives older-history prepends; the first work row does not.
+      key: `work:${finalReply.key}`,
       groups,
       durationMs,
       hasError: workGroupHasError(groups),
diff --git a/ui/src/pages/chat/components/chat-message.test.ts b/ui/src/pages/chat/components/chat-message.test.ts
index 7345899710dd..510ffcfd5476 100644
--- a/ui/src/pages/chat/components/chat-message.test.ts
+++ b/ui/src/pages/chat/components/chat-message.test.ts
@@ -525,6 +525,18 @@ describe("grouped chat rendering", () => {
     expect(userBubble.querySelector(".chat-bubble-actions")).toBeNull();
   });
 
+  it("does not replay an arrival animation when a message row mounts", () => {
+    const container = document.createElement("div");
+    renderAssistantMessage(container, {
+      role: "assistant",
+      content: "Stable transcript row",
+      timestamp: 1000,
+    });
+
+    const bubble = expectElement(container, ".chat-bubble", HTMLElement);
+    expect(bubble.classList.contains("fade-in")).toBe(false);
+  });
+
   it("uses the displayed answer for assistant message actions", () => {
     const container = document.createElement("div");
     const onOpenSidebar = vi.fn();
diff --git a/ui/src/pages/chat/components/chat-message.ts b/ui/src/pages/chat/components/chat-message.ts
index 638d7296ce27..1a265067b708 100644
--- a/ui/src/pages/chat/components/chat-message.ts
+++ b/ui/src/pages/chat/components/chat-message.ts
@@ -2131,7 +2131,6 @@ function renderGroupedMessage(
     "chat-bubble",
     isToolShell ? "chat-bubble--tool-shell" : "",
     opts.isStreaming ? "streaming" : "",
-    "fade-in",
   ]
     .filter(Boolean)
     .join(" ");
diff --git a/ui/src/styles/chat/grouped.css b/ui/src/styles/chat/grouped.css
index 89f2507a9ee8..5d1df28cf969 100644
--- a/ui/src/styles/chat/grouped.css
+++ b/ui/src/styles/chat/grouped.css
@@ -518,11 +518,6 @@ img.chat-avatar {
   box-shadow: none;
 }
 
-/* Fade-in animation for new messages */
-.chat-bubble.fade-in {
-  animation: fade-in 200ms ease-out;
-}
-
 @keyframes fade-in {
   from {
     opacity: 0;