refactor: extract minimal helpers from _dispatch, _dispatch_project and _create_task

Move the /tasks/* sub-route out of _dispatch into _dispatch_task_route
(query passed explicitly; the files/tree/thread branches use it), move
the push-subscription DELETE branch out of _dispatch_project into
_project_push_subscription_delete, and turn the goal-validation block
of _create_task into the pure module function
_validate_task_goal_options (returns error string instead of sending
400, caller sends it unchanged). Statements are moved verbatim except
indentation and the goal send+return -> return-error transform; no
behaviour change. server.py module split intentionally not done: it
remains a larger, higher-risk refactor.

Add test_longfunc_split covering the pure goal validator's success
paths and all eight error strings.

cloud/tests/test_longfunc_split.py

@@ -0,0 +1,91 @@
+"""长函数小步拆分单测：只测从 _create_task 抽出的纯函数。
+
+不跑真实模型回合、不联网、不碰 DB：_validate_task_goal_options
+只读 body/prompt/plan，错误串须与抽取前 _create_task 内联分支
+发出的 400 文案逐字一致（改动文案即本文件失败）。
+本文件不含任何真实密钥、token、证书或私钥。
+"""
+
+import sys
+import unittest
+from pathlib import Path
+
+try:
+    from cloud.server import (
+        CloudControlPlaneHandler,
+        _validate_task_goal_options,
+    )
+except ImportError:  # discover -s cloud/tests 时把项目根目录补进 sys.path
+    sys.path.insert(0, str(Path(__file__).resolve().parents[2]))
+    from cloud.server import (
+        CloudControlPlaneHandler,
+        _validate_task_goal_options,
+    )
+
+
+class ValidateTaskGoalOptionsTestCase(unittest.TestCase):
+    def test_new_goal_mode(self):
+        self.assertEqual(
+            _validate_task_goal_options(
+                {"goal_mode": 1}, "做 X", None, 0),
+            (1, "做 X", None, 0, None))
+
+    def test_goal_command_target_is_new_goal_mode(self):
+        self.assertEqual(
+            _validate_task_goal_options(
+                {}, "做 X", "做 X", 0),
+            (1, "做 X", None, 0, None))
+
+    def test_new_goal_mode_conflicts(self):
+        self.assertEqual(
+            _validate_task_goal_options(
+                {"goal_mode": 1}, "做 X", None, 1)[4],
+            "plan 模式与 goal 模式冲突（只读 vs 改文件）")
+        self.assertEqual(
+            _validate_task_goal_options(
+                {"goal_mode": 1, "verify_command": "make test"},
+                "做 X", None, 0)[4],
+            "goal 模式不需要验收命令（达标由模型宣告）")
+
+    def test_old_goal_defaults(self):
+        self.assertEqual(
+            _validate_task_goal_options({}, "p", None, 0),
+            (0, None, None, 3, None))
+
+    def test_old_goal_explicit(self):
+        self.assertEqual(
+            _validate_task_goal_options(
+                {"goal": "G", "verify_command": "make test",
+                 "goal_max_rounds": 5}, "p", None, 0),
+            (0, "G", "make test", 5, None))
+
+    def test_old_goal_errors(self):
+        # (body, plan, want_error)：plan+verify 冲突用例传 plan=1，
+        # 其余 plan=0。
+        cases = [
+            ({"goal": 123}, 0, "goal must be a string"),
+            ({"verify_command": 123}, 0, "verify_command must be a string"),
+            ({"verify_command": "make test"}, 1,
+             "plan 模式与 goal 模式冲突（只读 vs 改文件）"),
+            ({"goal_max_rounds": "x"}, 0,
+             "goal_max_rounds must be an integer"),
+            ({"goal_max_rounds": 0}, 0, "goal_max_rounds must be >= 1"),
+            ({"goal_max_rounds": 101}, 0, "goal_max_rounds 超过上限 100 轮"),
+        ]
+        for body, plan, want in cases:
+            self.assertEqual(
+                _validate_task_goal_options(body, "p", None, plan)[4],
+                want, body)
+
+    def test_split_helpers_exist(self):
+        # 结构锚点：两个路由助手须挂在 handler 上（行为由既有
+        # dispatch/任务/订阅测试覆盖，本文件不重复搭 HTTP 骨架）。
+        self.assertTrue(callable(
+            getattr(CloudControlPlaneHandler, "_dispatch_task_route")))
+        self.assertTrue(callable(
+            getattr(CloudControlPlaneHandler,
+                    "_project_push_subscription_delete")))
+
+
+if __name__ == "__main__":
+    unittest.main()