feat: 命令台子代理链路（主任务/模型子代理/委派子任务 + 过程调用实时同步）

host：链路条目带 thread 归属；delegate 向父链路文件写 agent-start/done 标记。服务端：GET /tasks/{id}/agents 聚合父链路 + 子链路文件成代理链（状态口径：委派以结束标记为准、无标记即进行中；模型子代理无结束信号时父任务运行中为进行中、否则未知）。命令台：新增子代理链路区，随 SSE 流防抖刷新；扁平链路也渲染 agent 标记。

tests/test_host_trace.py

@@ -6,6 +6,7 @@
 
 import json
 import os
+import shutil
 import sys
 import tempfile
 import unittest
@@ -130,6 +131,48 @@ class TraceFileTestCase(unittest.TestCase):
             self.assertEqual(len(lines), 1)
             self.assertEqual(json.loads(lines[0])["id"], "c1")
 
+    def test_summarize_carries_thread(self):
+        # 模型内子代理与主任务同文件时，服务端凭 thread 归属条目。
+        entries = _summarize_trace_item(
+            "item/completed",
+            {"item": {"type": "commandExecution", "id": "c1",
+                      "command": "ls"},
+             "threadId": "th-sub", "completedAtMs": 1700000000000})
+        self.assertEqual(entries[0]["thread"], "th-sub")
+        entries = _summarize_trace_item(
+            "item/completed",
+            {"item": {"type": "commandExecution", "id": "c2",
+                      "command": "ls"},
+             "completedAtMs": 1700000000000})
+        self.assertIsNone(entries[0]["thread"])
+
+    def test_append_trace_marker_to_parent_file(self):
+        # delegate 向父链路报到：路径清洗与 set_trace_file 一致，
+        # 写失败不抛（尽力而为，不影响回合）。
+        from host import _append_trace_marker, _trace_file_path
+        with tempfile.TemporaryDirectory() as d:
+            state_path = os.path.join(d, "host-state.json")
+            self.assertEqual(
+                _trace_file_path(state_path, "abc/def?id=1"),
+                os.path.join(d, "host-traces", "abc-def-id-1.jsonl"))
+            _append_trace_marker(
+                state_path, "parent task!",
+                {"kind": "agent-start", "id": "agent:rev",
+                 "name": "rev", "prompt": "review"})
+            path = os.path.join(d, "host-traces", "parent-task-.jsonl")
+            with open(path, encoding="utf-8") as f:
+                entry = json.loads(f.read().strip())
+            self.assertEqual(entry["kind"], "agent-start")
+            self.assertEqual(entry["name"], "rev")
+            # 目录被文件占住时也不抛。
+            blocker = os.path.join(d, "host-traces")
+            shutil.rmtree(blocker)
+            with open(blocker, "w", encoding="utf-8") as f:
+                f.write("x")
+            _append_trace_marker(state_path, "parent task!",
+                                 {"kind": "agent-done", "id": "agent:rev:done",
+                                  "name": "rev", "status": "completed"})
+
 
 if __name__ == "__main__":
     unittest.main()