fix(agent): switch roster node to inline (#37754)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

api/services/agent/composer_service.py

@@ -830,6 +830,16 @@ class AgentComposerService:
     ) -> WorkflowAgentNodeBinding:
         node_job = payload.node_job or WorkflowNodeJobConfig()
         if binding:
+            if cls._is_start_from_scratch_request(binding=binding, payload=payload):
+                return cls._switch_roster_binding_to_inline_agent(
+                    tenant_id=tenant_id,
+                    app_id=app_id,
+                    workflow_id=workflow_id,
+                    node_id=node_id,
+                    account_id=account_id,
+                    binding=binding,
+                    payload=payload,
+                )
             binding.node_job_config = node_job
             if payload.agent_soul is not None and binding.binding_type == WorkflowAgentBindingType.INLINE_AGENT:
                 current_snapshot = cls._require_version(
@@ -880,6 +890,46 @@ class AgentComposerService:
         db.session.flush()
         return binding
 
+    @classmethod
+    def _is_start_from_scratch_request(cls, *, binding: WorkflowAgentNodeBinding, payload: ComposerSavePayload) -> bool:
+        return (
+            binding.binding_type == WorkflowAgentBindingType.ROSTER_AGENT
+            and payload.binding is not None
+            and payload.binding.binding_type == WorkflowAgentBindingType.INLINE_AGENT.value
+        )
+
+    @classmethod
+    def _switch_roster_binding_to_inline_agent(
+        cls,
+        *,
+        tenant_id: str,
+        app_id: str,
+        workflow_id: str,
+        node_id: str,
+        account_id: str,
+        binding: WorkflowAgentNodeBinding,
+        payload: ComposerSavePayload,
+    ) -> WorkflowAgentNodeBinding:
+        if payload.binding and (payload.binding.agent_id or payload.binding.current_snapshot_id):
+            raise ValueError("Start from Scratch must not provide an existing inline agent binding.")
+
+        agent_soul = payload.agent_soul or AgentSoulConfig()
+        agent = cls._create_workflow_only_agent(
+            tenant_id=tenant_id,
+            app_id=app_id,
+            workflow_id=workflow_id,
+            node_id=node_id,
+            account_id=account_id,
+            agent_soul=agent_soul,
+        )
+        binding.binding_type = WorkflowAgentBindingType.INLINE_AGENT
+        binding.agent_id = agent.id
+        binding.current_snapshot_id = agent.active_config_snapshot_id
+        binding.node_job_config = payload.node_job or binding.node_job_config
+        binding.updated_by = account_id
+        db.session.flush()
+        return binding
+
     @classmethod
     def _save_to_current_version(
         cls,