diff --git a/src/langbot/pkg/api/http/controller/groups/monitoring.py b/src/langbot/pkg/api/http/controller/groups/monitoring.py
index aae227e25..5cbdf56c6 100644
--- a/src/langbot/pkg/api/http/controller/groups/monitoring.py
+++ b/src/langbot/pkg/api/http/controller/groups/monitoring.py
@@ -24,12 +24,21 @@ def parse_iso_datetime(datetime_str: str | None) -> datetime.datetime | None:
     return dt
 
 
-def validate_monitoring_window(start_time: datetime.datetime | None, end_time: datetime.datetime | None) -> None:
+def validate_monitoring_window(
+    start_time: datetime.datetime | None,
+    end_time: datetime.datetime | None,
+    *,
+    allow_point_window: bool = False,
+) -> None:
     """Bound explicit dashboard windows to one year without silently truncating them."""
     if start_time is None:
         return
     end = end_time or datetime.datetime.now(datetime.timezone.utc).replace(tzinfo=None)
-    if start_time >= end or end - start_time > datetime.timedelta(days=365):
+    if (
+        start_time > end
+        or (start_time == end and not allow_point_window)
+        or end - start_time > datetime.timedelta(days=365)
+    ):
         quart.abort(400, description='Monitoring time range must be positive and no longer than 365 days')
 
 
@@ -580,7 +589,8 @@ class MonitoringRouterGroup(group.RouterGroup):
             """Get detailed analysis for a specific session"""
             start_time = parse_iso_datetime(quart.request.args.get('startTime'))
             end_time = parse_iso_datetime(quart.request.args.get('endTime'))
-            validate_monitoring_window(start_time, end_time)
+            # Message pages can contain one timestamp; tool-call bounds are inclusive.
+            validate_monitoring_window(start_time, end_time, allow_point_window=True)
             analysis = await self.ap.monitoring_service.get_session_analysis(
                 request_context,
                 session_id,
diff --git a/tests/unit_tests/api/service/test_monitoring_sessions.py b/tests/unit_tests/api/service/test_monitoring_sessions.py
index 7451c9124..868f51589 100644
--- a/tests/unit_tests/api/service/test_monitoring_sessions.py
+++ b/tests/unit_tests/api/service/test_monitoring_sessions.py
@@ -183,6 +183,31 @@ async def test_analysis_fails_closed_and_scopes_statistics(service):
     assert result['session']['bot_id'] == 'b'
 
 
+async def test_single_message_analysis_without_tool_calls(service):
+    from langbot.pkg.api.http.controller.groups.monitoring import validate_monitoring_window
+    from werkzeug.exceptions import BadRequest
+
+    await service.record_session_start(context('a'), session_id='person_42', **resource('a'))
+    await service.record_message(context('a'), session_id='person_42', message_content='hi', **resource('a'))
+    row = (await service.ap.persistence_mgr.execute_async(sa.select(models.MonitoringMessage.timestamp))).one()
+    timestamp = row.timestamp
+    validate_monitoring_window(timestamp, timestamp, allow_point_window=True)
+    result = await service.get_session_analysis(
+        context(), 'person_42', bot_id='a', start_time=timestamp, end_time=timestamp
+    )
+    assert result['found'] is True
+    assert result['message_stats']['total'] == 1
+    assert result['tool_calls'] == []
+    for start, end in [
+        (timestamp + dt.timedelta(seconds=1), timestamp),
+        (timestamp, timestamp + dt.timedelta(days=366)),
+    ]:
+        with pytest.raises(BadRequest):
+            validate_monitoring_window(start, end, allow_point_window=True)
+    with pytest.raises(BadRequest):
+        validate_monitoring_window(timestamp, timestamp)
+
+
 async def test_activity_requires_bot_and_upsert_counts_racing_first_queries(service):
     for _ in range(2):
         await service.record_session_start(context('a'), session_id='person_42', **resource('a'))
diff --git a/web/src/app/home/pipelines/PipelineMigration.tsx b/web/src/app/home/pipelines/PipelineMigration.tsx
index 892022f37..d85b3931f 100644
--- a/web/src/app/home/pipelines/PipelineMigration.tsx
+++ b/web/src/app/home/pipelines/PipelineMigration.tsx
@@ -340,16 +340,12 @@ export default function PipelineMigration({
 
   return (
     <>
-      {(count > 0 || previewError || results.length > 0) && (
+      {(count > 0 || results.length > 0) && (
         <Alert className="mb-4 shrink-0 border-amber-200 bg-amber-50 text-amber-900 dark:border-amber-900/50 dark:bg-amber-950/30 dark:text-amber-200">
           <AlertTriangle aria-hidden="true" />
           <AlertTitle>{t('pipelineMigration.title')}</AlertTitle>
           <AlertDescription className="flex items-center justify-between gap-3 text-amber-800 dark:text-amber-200">
-            <span>
-              {previewError
-                ? t('pipelineMigration.previewError')
-                : t('pipelineMigration.detected', { count })}
-            </span>
+            <span>{t('pipelineMigration.detected', { count })}</span>
             <Button
               variant="outline"
               size="sm"
diff --git a/web/src/app/infra/http/BaseHttpClient.ts b/web/src/app/infra/http/BaseHttpClient.ts
index 0243c9a3c..d1c86022a 100644
--- a/web/src/app/infra/http/BaseHttpClient.ts
+++ b/web/src/app/infra/http/BaseHttpClient.ts
@@ -4,6 +4,7 @@ import axios, {
   AxiosResponse,
   AxiosError,
 } from 'axios';
+import i18n from 'i18next';
 import {
   clearActiveWorkspaceUuid,
   getActiveWorkspaceUuid,
@@ -79,6 +80,12 @@ export abstract class BaseHttpClient {
     // 请求拦截
     this.instance.interceptors.request.use(
       async (config) => {
+        // Account-only endpoints have no selected Workspace. Workspace routes
+        // resolve their persisted language and override this presentation hint.
+        // This is a LangBot backend hint, not part of the public Space API.
+        if (!this.disableToken) {
+          config.headers['X-LangBot-Language'] = i18n.language || 'en-US';
+        }
         // 客户端添加认证头
         if (typeof window !== 'undefined' && !this.disableToken) {
           const session = this.getSessionSync();