feat(workflow): support single-node execution and MCP Streamable HTTP protocol

- Add `run_single_node` method in workflow service for isolated node execution
- Refactor MCP client to support Streamable HTTP protocol (2025-03-26) with session ID handling, SSE/JSON response parsing, and proper initialized notification
- Update iteration node to conditionally initialize stream writer based on stream flag
- Improve cycle graph node invocation with checkpoint config passing

api/app/core/workflow/nodes/cycle_graph/iteration.py

@@ -70,7 +70,7 @@ class IterationRuntime:
         self.variable_pool = variable_pool
         self.cycle_nodes = cycle_nodes
         self.cycle_edges = cycle_edges
-        self.event_write = get_stream_writer()
+        self.event_write = get_stream_writer() if self.stream else (lambda x: None)
 
         self.output_value = None
         self.result: list = []
@@ -196,7 +196,7 @@ class IterationRuntime:
                         })
             result = graph.get_state(config=checkpoint).values
         else:
-            result = await graph.ainvoke(init_state)
+            result = await graph.ainvoke(init_state, config=checkpoint)
 
         output = child_pool.get_value(self.output_value)
         stopped = result["looping"] == 2

api/app/core/workflow/nodes/cycle_graph/loop.py

@@ -57,7 +57,7 @@ class LoopRuntime:
         self.looping = True
         self.variable_pool = variable_pool
         self.child_variable_pool = child_variable_pool
-        self.event_write = get_stream_writer()
+        self.event_write = get_stream_writer() if self.stream else (lambda x: None)
 
         self.checkpoint = RunnableConfig(
             configurable={
@@ -223,7 +223,7 @@ class LoopRuntime:
                         })
             return self.graph.get_state(config=self.checkpoint).values
         else:
-            return await self.graph.ainvoke(loopstate)
+            return await self.graph.ainvoke(loopstate, config=self.checkpoint)
 
     async def run(self):
         """

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

@@ -385,6 +385,7 @@ class HttpRequestNode(BaseNode):
                     logger.info(f"Node {self.node_id}: HTTP request succeeded")
                     response = HttpResponse(resp)
                     # Build raw request summary for process_data
+                    await resp.request.aread()
                     raw_request = (
                         f"{self.typed_config.method.upper()} {resp.request.url} HTTP/1.1\r\n"
                         + "".join(f"{k}: {v}\r\n" for k, v in resp.request.headers.items())