diff --git a/nanobot/webui/transcript.py b/nanobot/webui/transcript.py
index ee2734283..0d19a7119 100644
--- a/nanobot/webui/transcript.py
+++ b/nanobot/webui/transcript.py
@@ -1823,6 +1823,29 @@ def fork_boundary_message_count(lines: list[dict[str, Any]]) -> int | None:
     return None
 
 
+def has_pending_tool_calls(lines: list[dict[str, Any]]) -> bool:
+    """Return True when the selected transcript tail looks like an unfinished turn."""
+    for rec in reversed(lines):
+        ev = rec.get("event")
+        if ev == "turn_end":
+            return False
+        if ev == "user":
+            return False
+        if ev == "message":
+            return rec.get("kind") in {"tool_hint", "progress", "reasoning"}
+        if ev in {
+            "delta",
+            "stream_end",
+            "reasoning_delta",
+            "reasoning_end",
+            "file_edit",
+        }:
+            return True
+        if ev in {WEBUI_FORK_MARKER_EVENT}:
+            continue
+    return False
+
+
 def build_webui_thread_response(
     session_key: str,
     *,
@@ -1855,6 +1878,7 @@ def build_webui_thread_response(
         "schemaVersion": WEBUI_TRANSCRIPT_SCHEMA_VERSION,
         "sessionKey": session_key,
         "messages": msgs,
+        "has_pending_tool_calls": has_pending_tool_calls(lines),
     }
     if page is not None:
         page["loaded_message_count"] = len(msgs)
diff --git a/tests/utils/test_webui_transcript.py b/tests/utils/test_webui_transcript.py
index 0675b659a..4f0173400 100644
--- a/tests/utils/test_webui_transcript.py
+++ b/tests/utils/test_webui_transcript.py
@@ -290,6 +290,91 @@ def test_replay_delta_and_turn_end(tmp_path, monkeypatch) -> None:
     assert msgs[1]["latencyMs"] == 42
 
 
+def test_thread_response_does_not_mark_completed_message_tool_tail_pending(
+    tmp_path,
+    monkeypatch,
+) -> None:
+    monkeypatch.setattr("nanobot.config.paths.get_data_dir", lambda: tmp_path)
+    key = "websocket:cron-tail"
+    turn_id = "cron:job:run"
+    for ev in (
+        {
+            "event": "message",
+            "chat_id": "cron-tail",
+            "text": 'message({"content":"Cron test"})',
+            "kind": "tool_hint",
+            "tool_events": [{
+                "phase": "start",
+                "call_id": "call-message",
+                "name": "message",
+                "arguments": {"content": "Cron test"},
+            }],
+            "turn_id": turn_id,
+            "turn_phase": "activity",
+            "turn_seq": 5,
+        },
+        {
+            "event": "message",
+            "chat_id": "cron-tail",
+            "text": "Cron test",
+            "source": {"kind": "cron", "label": "one-min-test"},
+            "turn_id": turn_id,
+            "turn_phase": "answer",
+            "turn_seq": 6,
+        },
+        {
+            "event": "message",
+            "chat_id": "cron-tail",
+            "text": "",
+            "kind": "progress",
+            "tool_events": [{
+                "phase": "end",
+                "call_id": "call-message",
+                "name": "message",
+                "arguments": {"content": "Cron test"},
+                "result": "ok",
+            }],
+            "turn_id": turn_id,
+            "turn_phase": "activity",
+            "turn_seq": 7,
+        },
+        {
+            "event": "turn_end",
+            "chat_id": "cron-tail",
+            "turn_id": turn_id,
+            "turn_phase": "complete",
+            "turn_seq": 8,
+        },
+    ):
+        append_transcript_object(key, ev)
+
+    out = build_webui_thread_response(key)
+
+    assert out is not None
+    assert out["has_pending_tool_calls"] is False
+    assert out["messages"][-1]["kind"] == "trace"
+    assert out["messages"][-2]["content"] == "Cron test"
+
+
+def test_thread_response_marks_unfinished_tool_tail_pending(tmp_path, monkeypatch) -> None:
+    monkeypatch.setattr("nanobot.config.paths.get_data_dir", lambda: tmp_path)
+    key = "websocket:active-tail"
+    append_transcript_object(
+        key,
+        {
+            "event": "message",
+            "chat_id": "active-tail",
+            "text": 'exec({"command":"date"})',
+            "kind": "tool_hint",
+        },
+    )
+
+    out = build_webui_thread_response(key)
+
+    assert out is not None
+    assert out["has_pending_tool_calls"] is True
+
+
 def test_replay_preserves_turn_metadata(tmp_path, monkeypatch) -> None:
     monkeypatch.setattr("nanobot.config.paths.get_data_dir", lambda: tmp_path)
     key = "websocket:t-turn"
diff --git a/webui/src/hooks/useNanobotStream.ts b/webui/src/hooks/useNanobotStream.ts
index e53377bab..bac44ad00 100644
--- a/webui/src/hooks/useNanobotStream.ts
+++ b/webui/src/hooks/useNanobotStream.ts
@@ -8,6 +8,7 @@ import {
   normalizeToolProgressEvents,
   toolTraceLinesFromEvents,
 } from "@/lib/tool-traces";
+import { hasPendingAgentActivity } from "@/lib/activity-timeline";
 import type { StreamError } from "@/lib/nanobot-client";
 import type {
   InboundEvent,
@@ -450,12 +451,8 @@ export function useNanobotStream(
 } {
   const { client } = useClient();
   const [messages, setMessages] = useState<UIMessage[]>(initialMessages);
-  /** If the last loaded message is a trace row (e.g. "Using 2 tools"),
-   * the model was still processing when the page loaded — keep the
-   * loading spinner alive so the user sees the model is active. */
-  const initialStreaming = initialMessages.length > 0
-    ? initialMessages[initialMessages.length - 1].kind === "trace"
-    : false;
+  /** If history ends in unfinished agent activity, keep the loading spinner alive. */
+  const initialStreaming = hasPendingAgentActivity(initialMessages);
   const [isStreaming, setIsStreaming] = useState(initialStreaming || hasPendingToolCalls);
   /** Unix epoch seconds when the current user turn started; cleared on ``idle``. */
   const [runStartedAt, setRunStartedAt] = useState<number | null>(null);
@@ -694,9 +691,7 @@ export function useNanobotStream(
   useEffect(() => {
     setMessages(initialMessages);
     setIsStreaming(
-      (initialMessages.length > 0
-        ? initialMessages[initialMessages.length - 1].kind === "trace"
-        : false) || hasPendingToolCalls,
+      hasPendingAgentActivity(initialMessages) || hasPendingToolCalls,
     );
     setStreamError(null);
     setRunStartedAt(chatId ? client.getRunStartedAt(chatId) : null);
diff --git a/webui/src/hooks/useSessions.ts b/webui/src/hooks/useSessions.ts
index 7618b7e17..43adaadd6 100644
--- a/webui/src/hooks/useSessions.ts
+++ b/webui/src/hooks/useSessions.ts
@@ -8,6 +8,7 @@ import {
   fetchWebuiThread,
   listSessions,
 } from "@/lib/api";
+import { hasPendingAgentActivity } from "@/lib/activity-timeline";
 import { deriveTitle } from "@/lib/format";
 import type {
   ChatSummary,
@@ -29,6 +30,16 @@ function persistedMessagesToUi(messages: UIMessage[]): UIMessage[] {
   }));
 }
 
+function hasPendingToolCallsFromThread(
+  body: Awaited<ReturnType<typeof fetchWebuiThread>>,
+  messages: UIMessage[],
+): boolean {
+  if (typeof body?.has_pending_tool_calls === "boolean") {
+    return body.has_pending_tool_calls;
+  }
+  return hasPendingAgentActivity(messages);
+}
+
 /** Sidebar state: fetches the full session list and exposes create / delete actions. */
 export function useSessions(): {
   sessions: ChatSummary[];
@@ -257,8 +268,7 @@ export function useSessionHistory(key: string | null): {
           return;
         }
         const ui = persistedMessagesToUi(body.messages);
-        const last = ui[ui.length - 1];
-        const hasPending = last?.kind === "trace";
+        const hasPending = hasPendingToolCallsFromThread(body, ui);
         const forkBoundary = typeof body.fork_boundary_message_count === "number"
           ? Math.max(0, Math.min(body.fork_boundary_message_count, ui.length))
           : null;
@@ -342,13 +352,12 @@ export function useSessionHistory(key: string | null): {
           ? null
           : prev.forkBoundaryMessageCount + older.length;
         const nextMessages = [...older, ...prev.messages];
-        const last = nextMessages[nextMessages.length - 1];
         return {
           ...prev,
           messages: nextMessages,
           loadingOlder: false,
           error: null,
-          hasPendingToolCalls: last?.kind === "trace",
+          hasPendingToolCalls: hasPendingAgentActivity(nextMessages),
           forkBoundaryMessageCount: olderBoundary ?? shiftedBoundary,
           beforeCursor: body.page?.before_cursor ?? null,
           hasMoreBefore: body.page?.has_more_before === true,
diff --git a/webui/src/lib/activity-timeline.ts b/webui/src/lib/activity-timeline.ts
index 9f2b049b6..f1f912cef 100644
--- a/webui/src/lib/activity-timeline.ts
+++ b/webui/src/lib/activity-timeline.ts
@@ -52,6 +52,38 @@ export function isAgentActivityMember(message: UIMessage): boolean {
   return isReasoningOnlyAssistant(message) || message.kind === "trace";
 }
 
+export function hasPendingAgentActivity(messages: UIMessage[]): boolean {
+  if (messages.length === 0) return false;
+  const last = messages[messages.length - 1];
+  if (!isAgentActivityMember(last)) return false;
+
+  let trailingStart = messages.length - 1;
+  while (
+    trailingStart > 0
+    && isAgentActivityMember(messages[trailingStart - 1])
+  ) {
+    trailingStart -= 1;
+  }
+
+  const trailing = messages.slice(trailingStart);
+  if (trailing.some((message) => message.isStreaming || message.reasoningStreaming)) {
+    return true;
+  }
+
+  const previous = messages[trailingStart - 1];
+  if (!previous || previous.role !== "assistant" || isAgentActivityMember(previous)) {
+    return true;
+  }
+
+  const trailingTurnIds = new Set(
+    trailing
+      .map((message) => message.turnId)
+      .filter((turnId): turnId is string => typeof turnId === "string" && turnId.length > 0),
+  );
+  if (!previous.turnId) return trailingTurnIds.size > 0;
+  return trailingTurnIds.size > 0 && !trailingTurnIds.has(previous.turnId);
+}
+
 export function normalizeActivityTimeline(
   messages: UIMessage[],
   options: NormalizeActivityTimelineOptions = {},
diff --git a/webui/src/lib/types.ts b/webui/src/lib/types.ts
index f02a2e650..df51f0887 100644
--- a/webui/src/lib/types.ts
+++ b/webui/src/lib/types.ts
@@ -881,6 +881,7 @@ export interface WebuiThreadPersistedPayload {
   savedAt?: string;
   messages: UIMessage[];
   fork_boundary_message_count?: number;
+  has_pending_tool_calls?: boolean;
   page?: WebuiThreadPagePayload;
   workspace_scope?: WorkspaceScopePayload;
 }
diff --git a/webui/src/tests/useNanobotStream.test.tsx b/webui/src/tests/useNanobotStream.test.tsx
index dcec94df5..b983fc193 100644
--- a/webui/src/tests/useNanobotStream.test.tsx
+++ b/webui/src/tests/useNanobotStream.test.tsx
@@ -180,6 +180,36 @@ describe("useNanobotStream", () => {
     });
   });
 
+  it("does not start streaming from completed trailing activity after an answer", () => {
+    const fake = fakeClient();
+    const initialMessages = [
+      {
+        id: "a1",
+        role: "assistant" as const,
+        content: "Cron test",
+        turnId: "cron:run",
+        createdAt: Date.now(),
+      },
+      {
+        id: "t1",
+        role: "tool" as const,
+        kind: "trace" as const,
+        content: "message({})",
+        traces: ["message({})"],
+        turnId: "cron:run",
+        createdAt: Date.now(),
+      },
+    ];
+
+    const { result } = renderHook(
+      () => useNanobotStream("chat-cron-done", initialMessages),
+      { wrapper: wrap(fake.client) },
+    );
+
+    expect(result.current.messages.at(-1)?.kind).toBe("trace");
+    expect(result.current.isStreaming).toBe(false);
+  });
+
   it("drops pending stream work when switching chats", async () => {
     const fake = fakeClient();
     const { result, rerender } = renderHook(
diff --git a/webui/src/tests/useSessions.test.tsx b/webui/src/tests/useSessions.test.tsx
index 323f67ee7..148bf4628 100644
--- a/webui/src/tests/useSessions.test.tsx
+++ b/webui/src/tests/useSessions.test.tsx
@@ -416,6 +416,40 @@ describe("useSessions", () => {
     expect(result.current.hasPendingToolCalls).toBe(true);
   });
 
+  it("uses the server pending flag for completed tails that still end with trace rows", async () => {
+    vi.mocked(api.fetchWebuiThread).mockResolvedValue({
+      schemaVersion: 3,
+      has_pending_tool_calls: false,
+      messages: [
+        {
+          id: "a1",
+          role: "assistant",
+          content: "Cron test",
+          turnId: "cron:run",
+          createdAt: 1,
+        },
+        {
+          id: "t1",
+          role: "tool",
+          kind: "trace",
+          content: "message({})",
+          traces: ["message({})"],
+          turnId: "cron:run",
+          createdAt: 2,
+        },
+      ],
+    });
+
+    const { result } = renderHook(() => useSessionHistory("websocket:chat-cron-done"), {
+      wrapper: wrap(fakeClient()),
+    });
+
+    await waitFor(() => expect(result.current.loading).toBe(false));
+
+    expect(result.current.messages.at(-1)?.kind).toBe("trace");
+    expect(result.current.hasPendingToolCalls).toBe(false);
+  });
+
   it("does not flag transcript as pending when last row is not a trace", async () => {
     vi.mocked(api.fetchWebuiThread).mockResolvedValue({
       schemaVersion: 3,