diff --git a/extensions/codex/src/app-server/context-compaction-activity.test.ts b/extensions/codex/src/app-server/context-compaction-activity.test.ts
new file mode 100644
index 000000000000..49bb90d820e0
--- /dev/null
+++ b/extensions/codex/src/app-server/context-compaction-activity.test.ts
@@ -0,0 +1,70 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { persistCodexContextCompactionActivity } from "./context-compaction-activity.js";
+
+const appendMessage = vi.hoisted(() => vi.fn());
+const publishUpdate = vi.hoisted(() => vi.fn());
+
+vi.mock("openclaw/plugin-sdk/session-transcript-runtime", () => ({
+  appendSessionTranscriptMessageByIdentity: appendMessage,
+  publishSessionTranscriptUpdateByIdentity: publishUpdate,
+}));
+
+beforeEach(() => {
+  appendMessage.mockReset();
+  publishUpdate.mockReset();
+});
+
+describe("persistCodexContextCompactionActivity", () => {
+  it("publishes one model-excluded activity and leaves replay deduplication to transcript identity", async () => {
+    appendMessage
+      .mockImplementationOnce(async (params: { message: unknown }) => ({
+        appended: true,
+        message: params.message,
+        messageId: "activity-message",
+      }))
+      .mockResolvedValueOnce({
+        appended: false,
+        message: {},
+        messageId: "activity-message",
+      });
+    const params = {
+      run: {
+        runId: "run-1",
+        workspaceDir: "/workspace",
+        sessionTarget: {
+          agentId: "main",
+          sessionId: "session-1",
+          sessionKey: "agent:main:dashboard:session-1",
+          storePath: "/state/openclaw-agent.sqlite",
+        },
+      },
+      threadId: "thread-1",
+      turnId: "turn-1",
+      itemId: "compact-1",
+      timestamp: 123,
+    } as Parameters<typeof persistCodexContextCompactionActivity>[0];
+
+    await persistCodexContextCompactionActivity(params);
+    await persistCodexContextCompactionActivity(params);
+
+    expect(appendMessage).toHaveBeenCalledTimes(2);
+    expect(appendMessage.mock.calls[0]?.[0]).toMatchObject({
+      eventId: "codex-context-compaction:thread-1:turn-1:compact-1",
+      message: {
+        role: "custom",
+        customType: "openclaw.context-compaction",
+        content: "Context compacted",
+        display: true,
+        excludeFromContext: true,
+        idempotencyKey: "codex-context-compaction:thread-1:turn-1:compact-1",
+      },
+    });
+    expect(publishUpdate).toHaveBeenCalledOnce();
+    expect(publishUpdate.mock.calls[0]?.[0]).toMatchObject({
+      update: {
+        messageId: "activity-message",
+        runId: "run-1",
+      },
+    });
+  });
+});
diff --git a/packages/agent-core/src/harness/session/session-context.test.ts b/packages/agent-core/src/harness/session/session-context.test.ts
index 412f32837eaf..176cddee30b0 100644
--- a/packages/agent-core/src/harness/session/session-context.test.ts
+++ b/packages/agent-core/src/harness/session/session-context.test.ts
@@ -133,6 +133,19 @@ function toolResultEntry(
 }
 
 describe("buildSessionContext", () => {
+  it("keeps display-only custom activity out of model input", () => {
+    const activity = {
+      role: "custom" as const,
+      customType: "openclaw.context-compaction",
+      content: "Context compacted",
+      display: true,
+      excludeFromContext: true,
+      timestamp: Date.parse(timestamp),
+    };
+
+    expect(convertToLlm([activity])).toEqual([]);
+  });
+
   it("keeps private shell executions in history without projecting them into context", () => {
     const hiddenEntry = bashEntry("hidden", "initial", "private shell output", true);
     const visibleEntry = bashEntry("visible", "hidden", "visible shell output", false);
diff --git a/ui/src/pages/chat/chat-thread-grouping.ts b/ui/src/pages/chat/chat-thread-grouping.ts
index d1e4ecfa5ce7..64236e2a5ba4 100644
--- a/ui/src/pages/chat/chat-thread-grouping.ts
+++ b/ui/src/pages/chat/chat-thread-grouping.ts
@@ -86,12 +86,18 @@ export function groupMessages(items: ChatItem[]): Array<ChatItem | MessageGroup>
       currentGroup?.role === "assistant" &&
       isKeyedAssistantStreamFallbackMessage(currentGroup.messages[0]?.message) !==
         isKeyedAssistantStreamFallbackMessage(item.message);
+    const splitsRuntimeActivity =
+      role === "assistant" &&
+      currentGroup?.role === "assistant" &&
+      isContextCompactionActivity(currentGroup.messages[0]?.message) !==
+        isContextCompactionActivity(item.message);
 
     if (
       !currentGroup ||
       startsProjectedTurn ||
       currentGroup.role !== role ||
       splitsAssistantCommentary ||
+      splitsRuntimeActivity ||
       (shouldSplitBySender &&
         (currentGroup.senderLabel !== senderLabel ||
           senderIdentityKey(currentGroup.sender) !== senderIdentityKey(sender)))
@@ -542,14 +548,15 @@ export function assistantGroupCanOwnActiveRunStatus(group: MessageGroup): boolea
   return (
     group.role.toLowerCase() === "assistant" &&
     !assistantGroupIsForwardedBoundary(group) &&
-    !group.messages.every(
-      ({ message }) =>
-        asRecord(asRecord(message)?.["__openclaw"])?.runtimeActivityKind === "context_compaction",
-    ) &&
+    !group.messages.every(({ message }) => isContextCompactionActivity(message)) &&
     groupHasVisibleReplyContent(group)
   );
 }
 
+function isContextCompactionActivity(message: unknown): boolean {
+  return asRecord(asRecord(message)?.["__openclaw"])?.runtimeActivityKind === "context_compaction";
+}
+
 // History carries no final-vs-commentary marker (commentary exists only as
 // live stream segments), so the last assistant group with visible content
 // stands in for the final reply. Turns whose last content is commentary
diff --git a/ui/src/pages/chat/chat-thread.test.ts b/ui/src/pages/chat/chat-thread.test.ts
index 8c7154e12a7f..93919ac98e0f 100644
--- a/ui/src/pages/chat/chat-thread.test.ts
+++ b/ui/src/pages/chat/chat-thread.test.ts
@@ -757,6 +757,35 @@ describe("collapseCompletedTurnWork", () => {
     expect(requireGroup(items[2]).role).toBe("assistant");
   });
 
+  it("keeps durable context compaction inside completed work instead of treating it as the reply", () => {
+    const items = collapsedItems({
+      messages: [
+        userMessage("do it", 1_000),
+        {
+          role: "custom",
+          customType: "openclaw.context-compaction",
+          content: "Context compacted",
+          display: true,
+          excludeFromContext: true,
+          timestamp: 2_000,
+        },
+        assistantMessage("All done.", 3_000),
+      ],
+    });
+
+    expect(items.map((item) => item.kind)).toEqual(["group", "work-group", "group"]);
+    const work = requireWorkGroup(items[1]);
+    expect(work.groups).toHaveLength(1);
+    expect(work.groups[0]?.messages[0]?.message).toMatchObject({
+      role: "assistant",
+      content: [{ type: "text", text: "Context compacted" }],
+      __openclaw: { runtimeActivityKind: "context_compaction" },
+    });
+    expect(requireGroup(items[2]).messages[0]?.message).toMatchObject({
+      content: "All done.",
+    });
+  });
+
   it.each([
     {
       role: "assistant",