fix: preserve optional task instruction variables for OpenCode

backend/services/background_tasks/opencode.py

@@ -82,8 +82,12 @@ class OpenCodeExecutor:
                     if self.config.get("model_provider_id") and self.config.get("model_id"):
                         payload["model"] = {"providerID": self.config["model_provider_id"], "modelID": self.config["model_id"]}
                     backend = self.config.get("_backend") or {}
+                    from models import AssistantConfig
                     from services.runtime_variables import DynamicVariableStore
-                    store = DynamicVariableStore(self.config.get("_variables") or {})
+                    store = DynamicVariableStore.from_config(AssistantConfig(
+                        dynamic_variables=self.config.get("_variables") or {},
+                        dynamic_variable_definitions=self.config.get("_variable_definitions") or {},
+                    ))
                     assistant_instructions = store.render(str(backend.get("instructions") or ""))
                     instructions = "\n\n".join(value for value in (self.config.get("instructions"), assistant_instructions) if value)
                     if instructions:

backend/tests/test_opencode_tasks.py

@@ -36,7 +36,7 @@ class OpenCodeTaskTest(unittest.IsolatedAsyncioTestCase):
                 self.assertEqual(payload["messageID"], "msg_test")
                 self.assertEqual(payload["agent"], "build")
                 self.assertEqual(payload["model"], {"providerID": "test-provider", "modelID": "test-model"})
-                self.assertEqual(payload["system"], "通用说明\n\n项目 demo")
+                self.assertEqual(payload["system"], "通用说明\n\n项目 demo；可选信息：")
                 submitted = True
                 return httpx.Response(204)
             if request.url.path.endswith("/message"):
@@ -48,8 +48,9 @@ class OpenCodeTaskTest(unittest.IsolatedAsyncioTestCase):
             raise AssertionError(request.url)
         executor = OpenCodeExecutor({"url": "https://remote.test", "directory": "/workspace/demo", "agent": "build",
                                      "model_provider_id": "test-provider", "model_id": "test-model",
-                                     "instructions": "通用说明", "_backend": {"instructions": "项目 {{project}}"},
-                                     "_variables": {"project": "demo"}}, {}, transport=httpx.MockTransport(respond))
+                                     "instructions": "通用说明", "_backend": {"instructions": "项目 {{project}}；可选信息：{{optional}}"},
+                                     "_variables": {"project": "demo"},
+                                     "_variable_definitions": {"optional": {"type": "string", "required": False}}}, {}, transport=httpx.MockTransport(respond))
         async def emit(event):
             updates.append(event)
         result = await executor.run(handle, "修复测试", emit)

implement-stage/task-backends/BUILD_NOTE.md

@@ -13,6 +13,7 @@
 - F1：12项资源专项测试通过，连同原生主线、桥接、生命周期累计33项通过，exit 0；真实隔离 PostgreSQL 17 完成0026旧数据→0027迁移及CRUD/助手复制/运行时解析，见database-smoke.json。
 - F2：make test-backend，391项测试通过，exit 0；包含真实 Pipecat BackendLLMWorker 与模拟模型的13项Reasoner/服务主线检查、绑定指令来源、OpenCode固定agent/model/system负载及现有回归。
 - F3：TypeScript、lint及4项前端契约测试通过，exit 0；lint保留既有BatchTestPage警告。生产构建并入F4。
+- F4自动检查：`make test` exit 0（391项后端、4项前端契约、lint、production build、5项契约快照）；隔离数据库验证通过。补齐OpenCode可选变量行为后，再次运行391项后端检查，exit 0。浏览器验收和独立审阅正在补齐。
 
 ## Deferred
 - 真实模型/OpenCode联调：尚无服务地址与凭据。