fix(ui): reuse persisted text during chat streaming (#146831)

ui/src/pages/chat/chat-gateway.test.ts

@@ -824,6 +824,58 @@ describe("handleChatGatewayEvent", () => {
     expect(state.chatStream).toBe(expected);
   });
 
+  it("reuses persisted text across live deltas and refreshes replaced messages", () => {
+    const persistedMessage = (id: string, text: string) => {
+      const readContent = vi.fn(() => [{ type: "text", text }]);
+      return {
+        readContent,
+        message: {
+          role: "assistant",
+          get content() {
+            return readContent();
+          },
+          __openclaw: { id, runId: "run-1" },
+        },
+      };
+    };
+    const first = persistedMessage("part-a", "A");
+    const second = persistedMessage("part-b", "B");
+    const state = createState({
+      chatRunId: "run-1",
+      chatMessages: [first.message, second.message],
+    });
+    const receiveDelta = (text: string) => {
+      expect(
+        handleChatGatewayEvent(state, {
+          runId: "run-1",
+          sessionKey: "main",
+          state: "delta",
+          message: createTextChatMessage("assistant", text),
+        }),
+      ).toBe("delta");
+      return visibleCurrentAssistantStreamTail(state, () => false);
+    };
+
+    expect(receiveDelta("ABC")).toBe("C");
+    expect(first.readContent).toHaveBeenCalled();
+    expect(second.readContent).toHaveBeenCalled();
+    first.readContent.mockClear();
+    second.readContent.mockClear();
+
+    for (const text of ["ABCD", "ABCDE", "ABCDEF"]) {
+      expect(receiveDelta(text)).toBe(text.slice(2));
+    }
+    expect(first.readContent).not.toHaveBeenCalled();
+    expect(second.readContent).not.toHaveBeenCalled();
+
+    const replacement = persistedMessage("part-b", "BC");
+    state.chatMessages = [first.message, replacement.message];
+    expect(receiveDelta("ABCDEFG")).toBe("DEFG");
+    expect(replacement.readContent).toHaveBeenCalled();
+    expect(first.readContent).not.toHaveBeenCalled();
+    expect(second.readContent).not.toHaveBeenCalled();
+  });
+
   it("adopts the run id for selected-session live deltas observed from another channel", () => {
     const state = createState({
       sessionKey: "agent:main:feishu:direct:peer-1",

ui/src/pages/chat/stream-causal-boundary.ts

@@ -9,7 +9,7 @@ import {
   streamSegmentUsesAccumulatedText,
   type ChatStreamSegment,
 } from "../../lib/chat/chat-types.ts";
-import { extractText } from "../../lib/chat/message-extract.ts";
+import { extractText, extractTextCached } from "../../lib/chat/message-extract.ts";
 import { userTurnRunId } from "./chat-thread-items.ts";
 import { isKeyedAssistantStreamFallbackMessage } from "./chat-thread-run-identity.ts";
 
@@ -236,7 +236,7 @@ export function resolveCumulativeAssistantTail(
     const identity = readSessionMessageIdentity(message);
     const persistedText =
       identity?.runId === runId && !isKeyedAssistantStreamFallbackMessage(message)
-        ? extractText(message)
+        ? extractTextCached(message)
         : null;
     if (
       identity?.role === "assistant" &&
@@ -255,7 +255,7 @@ export function resolveCumulativeAssistantTail(
     return identity?.role === "assistant" &&
       (!identity.runId || identity.runId === runId) &&
       !isKeyedAssistantStreamFallbackMessage(message)
-      ? extractText(message)
+      ? extractTextCached(message)
       : null;
   });
   return resolveAssistantTextTail(persistedTexts, cumulativeText);