diff --git a/api/agent_sessions.py b/api/agent_sessions.py
index 1bdaf48b..7d65bc57 100644
--- a/api/agent_sessions.py
+++ b/api/agent_sessions.py
@@ -527,6 +527,10 @@ def read_session_lineage_metadata(db_path: Path, session_ids: list[str] | set[st
                 entry['relationship_type'] = 'child_session'
                 entry['parent_title'] = parent_row.get('title')
                 entry['parent_source'] = parent_row.get('source')
+                parent_source = str(parent_row.get('source') or '').strip().lower()
+                child_source = str(row.get('source') or '').strip().lower()
+                if parent_source and child_source and parent_source != child_source:
+                    entry['_cross_surface_child_session'] = True
                 parent_root = _continuation_root_id(rows, parent_id)
                 if parent_root:
                     entry['_parent_lineage_root_id'] = parent_root
diff --git a/static/sessions.js b/static/sessions.js
index 7ee8214e..2bfaeaff 100644
--- a/static/sessions.js
+++ b/static/sessions.js
@@ -1870,6 +1870,10 @@ function _attachChildSessionsToSidebarRows(collapsedRows, rawSessions){
   const orphans=[];
   for(const child of rawSessions||[]){
     if(!_isChildSession(child)) continue;
+    if(child._cross_surface_child_session){
+      orphans.push({...child,_orphan_child_session:true});
+      continue;
+    }
     const parentSid=child.parent_session_id;
     let parentRow=visibleBySid.get(parentSid);
     let parentSegment=null;
diff --git a/tests/test_session_lineage_collapse.py b/tests/test_session_lineage_collapse.py
index f68b3779..868c416b 100644
--- a/tests/test_session_lineage_collapse.py
+++ b/tests/test_session_lineage_collapse.py
@@ -126,6 +126,8 @@ console.log(JSON.stringify({{sid: collapsed[0].session_id, containsRoot: _sessio
     assert '"containsRoot":true' in result
 
 
+
+
 def test_sidebar_attaches_child_sessions_to_collapsed_hidden_parent_lineage():
     js = SESSIONS_JS_PATH.read_text(encoding="utf-8")
     source = f"""
@@ -162,3 +164,47 @@ console.log(JSON.stringify(attached));
     assert [row["session_id"] for row in rows] == ["tip"]
     assert rows[0]["_child_session_count"] == 1
     assert rows[0]["_child_sessions"][0]["session_id"] == "child"
+
+
+def test_cross_surface_webui_child_session_remains_top_level_when_parent_is_messaging():
+    js = SESSIONS_JS_PATH.read_text(encoding="utf-8")
+    source = f"""
+const src = {js!r};
+function extractFunc(name) {{
+  const re = new RegExp('function\\\\s+' + name + '\\\\s*\\\\(');
+  const start = src.search(re);
+  if (start < 0) throw new Error(name + ' not found');
+  let i = src.indexOf('{{', start);
+  let depth = 1; i++;
+  while (depth > 0 && i < src.length) {{
+    if (src[i] === '{{') depth++;
+    else if (src[i] === '}}') depth--;
+    i++;
+  }}
+  return src.slice(start, i);
+}}
+eval(extractFunc('_isChildSession'));
+eval(extractFunc('_sidebarLineageKeyForRow'));
+eval(extractFunc('_attachChildSessionsToSidebarRows'));
+const collapsed = [{{session_id:'telegram_parent', title:'Telegram parent', source_label:'Telegram'}}];
+const raw = [
+  collapsed[0],
+  {{
+    session_id:'webui_tip',
+    title:'Current WebUI continuation',
+    parent_session_id:'telegram_parent',
+    relationship_type:'child_session',
+    parent_source:'telegram',
+    source_label:'Telegram',
+    session_source:'messaging',
+    raw_source:'telegram',
+    _cross_surface_child_session:true,
+  }},
+];
+const rows = _attachChildSessionsToSidebarRows(collapsed, raw);
+console.log(JSON.stringify(rows));
+"""
+    rows = json.loads(_run_node(source))
+    assert [row["session_id"] for row in rows] == ["telegram_parent", "webui_tip"]
+    assert rows[1].get("_orphan_child_session") is True
+    assert "_child_sessions" not in rows[0]
diff --git a/tests/test_session_lineage_metadata_api.py b/tests/test_session_lineage_metadata_api.py
index fbd3381b..f070bd7e 100644
--- a/tests/test_session_lineage_metadata_api.py
+++ b/tests/test_session_lineage_metadata_api.py
@@ -45,14 +45,14 @@ def _ensure_state_db(path):
     return conn
 
 
-def _insert_state_row(conn, sid, *, parent=None, ended_at=None, end_reason=None, started_at=None):
+def _insert_state_row(conn, sid, *, parent=None, ended_at=None, end_reason=None, started_at=None, source='webui'):
     conn.execute(
         """
         INSERT INTO sessions
         (id, source, title, model, started_at, message_count, parent_session_id, ended_at, end_reason)
-        VALUES (?, 'webui', ?, 'openai/gpt-5', ?, 2, ?, ?, ?)
+        VALUES (?, ?, ?, 'openai/gpt-5', ?, 2, ?, ?, ?)
         """,
-        (sid, sid, started_at or time.time(), parent, ended_at, end_reason),
+        (sid, source, sid, started_at or time.time(), parent, ended_at, end_reason),
     )
     conn.commit()
 
@@ -202,3 +202,35 @@ def test_cli_close_parent_preserves_cross_surface_continuation_lineage(_isolate)
         assert rows["lineage_api_webui_child"].get("_lineage_root_id") == "lineage_api_cli_parent"
     finally:
         conn.close()
+
+
+def test_cross_surface_child_session_metadata_marks_orphan_top_level_candidate(_isolate):
+    conn = _ensure_state_db(_isolate)
+    t0 = time.time() - 100
+    try:
+        _save_webui_session("lineage_api_telegram_parent", title="Telegram parent", updated_at=t0)
+        _save_webui_session("lineage_api_webui_tip", title="WebUI tip", updated_at=t0 + 10)
+        _insert_state_row(
+            conn,
+            "lineage_api_telegram_parent",
+            source="telegram",
+            started_at=t0,
+            ended_at=t0 + 5,
+            end_reason="compression",
+        )
+        _insert_state_row(
+            conn,
+            "lineage_api_webui_tip",
+            source="webui",
+            parent="lineage_api_telegram_parent",
+            started_at=t0 + 6,
+        )
+
+        rows = {row["session_id"]: row for row in all_sessions()}
+        tip = rows["lineage_api_webui_tip"]
+
+        assert tip.get("relationship_type") == "child_session"
+        assert tip.get("parent_source") == "telegram"
+        assert tip.get("_cross_surface_child_session") is True
+    finally:
+        conn.close()