From 36ee986d5548ccc382a598c834f4edcd3953c965 Mon Sep 17 00:00:00 2001
From: TYY-2005 <tyy1659579788@gmail.com>
Date: Tue, 20 Oct 2026 09:57:28 +0800
Subject: [PATCH] fix(frontend): restore thinking-only steps after reconnect
 (#7144)

* fix(frontend): restore thinking-only steps after reconnect

* docs(frontend): explain reconnect answer boundary

---------

Co-authored-by: TYY-2005 <TYY-2005@users.noreply.github.com>
Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
---
 frontend/src/core/threads/hooks.ts            |  6 ++-
 .../unit/core/threads/message-merge.test.ts   | 37 +++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/frontend/src/core/threads/hooks.ts b/frontend/src/core/threads/hooks.ts
index 56b91d7f31..1ea79991f9 100644
--- a/frontend/src/core/threads/hooks.ts
+++ b/frontend/src/core/threads/hooks.ts
@@ -21,7 +21,7 @@ import { getBackendBaseURL } from "../config";
 import { useI18n } from "../i18n/hooks";
 import { getMessageRunId } from "../messages/run-duration";
 import {
-  hasContent,
+  extractContentFromMessage,
   hasToolCalls,
   isHiddenFromUIMessage,
 } from "../messages/utils";
@@ -1072,7 +1072,9 @@ export function restoreReconnectedTurnMessageOrder(
     if (
       message.type === "ai" &&
       !isHiddenFromUIMessage(message) &&
-      hasContent(message) &&
+      // Thinking-only blocks (Anthropic) are not completed answers: require
+      // extractable text/image content to close the turn.
+      extractContentFromMessage(message).length > 0 &&
       !hasToolCalls(message)
     ) {
       candidateStart = index + 1;
diff --git a/frontend/tests/unit/core/threads/message-merge.test.ts b/frontend/tests/unit/core/threads/message-merge.test.ts
index 2e5af0bc1c..0b6800217c 100644
--- a/frontend/tests/unit/core/threads/message-merge.test.ts
+++ b/frontend/tests/unit/core/threads/message-merge.test.ts
@@ -2503,6 +2503,43 @@ test("reconnected turn order treats a content-only streaming text as a boundary"
   ).toEqual([streamingText, human, toolStep, laterStep]);
 });
 
+test("reconnected turn order does not treat Anthropic thinking blocks as a completed answer", () => {
+  const thinkingStep = {
+    id: "thinking-step",
+    type: "ai",
+    content: [{ type: "thinking", thinking: "Still analyzing" }],
+    run_id: "run-r",
+  } as unknown as Message;
+  const toolStep = {
+    id: "tool-step",
+    type: "ai",
+    content: "",
+    tool_calls: [{ id: "tc-1", name: "read_file", args: {} }],
+    run_id: "run-r",
+  } as unknown as Message;
+  const human = {
+    id: "human-r",
+    type: "human",
+    content: "Question",
+  } as Message;
+  const laterStep = {
+    id: "later",
+    type: "ai",
+    content: "",
+    tool_calls: [{ id: "tc-2", name: "write_file", args: {} }],
+    run_id: "run-r",
+  } as unknown as Message;
+
+  expect(
+    restoreReconnectedTurnMessageOrder([
+      thinkingStep,
+      toolStep,
+      human,
+      laterStep,
+    ]),
+  ).toEqual([human, thinkingStep, toolStep, laterStep]);
+});
+
 test("rendered message ledger does not retain explicitly superseded messages", () => {
   const retained = {
     id: "retained-answer",