feat(workflow): parse and substitute template variables in node configurations

- Implement regex matching for {{xxx}} template variable format.
- Enable recursive parsing of all string template variables within node configurations.
- Resolve and substitute template variables with runtime values during input data extraction.
- Support dynamic parsing and substitution of file selector variables in the document extraction node.
- Make strict template variable mode optional and introduce support for default values.

api/app/core/workflow/nodes/base_node.py

@@ -1,5 +1,6 @@
 import asyncio
 import logging
+import re
 import time
 import uuid
 from abc import ABC, abstractmethod
@@ -22,6 +23,9 @@ from app.services.multimodal_service import MultimodalService
 
 logger = logging.getLogger(__name__)
 
+# 匹配模板变量 {{xxx}} 的正则
+_TEMPLATE_PATTERN = re.compile(r"\{\{.*?\}\}")
+
 
 class NodeExecutionError(Exception):
     """节点执行失败异常。
@@ -503,10 +507,29 @@ class BaseNode(ABC):
             variable_pool: The variable pool used for reading and writing variables.
 
         Returns:
-            A dictionary containing the node's input data.
+            A dictionary containing the node's input data with all template
+            variables resolved to their actual runtime values.
         """
-        # Default implementation returns the node configuration
-        return {"config": self.config}
+        return {"config": self._resolve_config(self.config, variable_pool)}
+
+    @staticmethod
+    def _resolve_config(config: Any, variable_pool: VariablePool) -> Any:
+        """递归解析 config 中的模板变量，将 {{xxx}} 替换为实际值。
+
+        Args:
+            config: 节点的原始配置（可能包含模板变量）。
+            variable_pool: 变量池，用于解析模板变量。
+
+        Returns:
+            解析后的配置，所有字符串中的 {{变量}} 已被替换为真实值。
+        """
+        if isinstance(config, str) and _TEMPLATE_PATTERN.search(config):
+            return BaseNode._render_template(config, variable_pool, strict=False)
+        elif isinstance(config, dict):
+            return {k: BaseNode._resolve_config(v, variable_pool) for k, v in config.items()}
+        elif isinstance(config, list):
+            return [BaseNode._resolve_config(item, variable_pool) for item in config]
+        return config
 
     def _extract_output(self, business_result: Any) -> Any:
         """Extracts the actual output from the business result.

api/app/core/workflow/nodes/document_extractor/node.py

@@ -121,7 +121,10 @@ class DocExtractorNode(BaseNode):
         return business_result
 
     def _extract_input(self, state: WorkflowState, variable_pool: VariablePool) -> dict[str, Any]:
-        return {"file_selector": self.config.get("file_selector")}
+        file_selector = self.config.get("file_selector", "")
+        # 将变量选择器（如 sys.files）解析为实际值
+        resolved = self.get_variable(file_selector, variable_pool, strict=False, default=file_selector)
+        return {"file_selector": resolved}
 
     async def execute(self, state: WorkflowState, variable_pool: VariablePool) -> Any:
         config = DocExtractorNodeConfig(**self.config)