Enhance conversation history and runtime variable management

- Update ConversationRecorder to include source and nodeId metadata in transcripts for better context tracking.
- Introduce optional variable handling in DynamicVariableStore, allowing for unset variables to be rendered as empty without raising errors.
- Refactor WorkflowBrain to apply turn configurations and manage interaction policies dynamically, improving agent responsiveness.
- Implement tests to ensure proper handling of updated session variables and workflow metadata in various scenarios.

frontend/src/components/workflow/specs.ts

@@ -3,7 +3,8 @@
 import * as LucideIcons from "lucide-react";
 import { Circle, type LucideIcon } from "lucide-react";
 
-import type { NodeSpecDto } from "@/lib/api";
+import type { NodeSpecDto, TurnConfig } from "@/lib/api";
+import { defaultTurnConfig } from "@/lib/turn-config";
 
 export type WorkflowNodeType = "start" | "agent" | "action" | "handoff" | "end";
 export type ContextPolicy = "inherit" | "fresh";
@@ -37,6 +38,8 @@ export type WorkflowNodeData = {
   llmResourceId?: string;
   asrResourceId?: string;
   ttsResourceId?: string;
+  enableInterrupt?: boolean;
+  turnConfig?: TurnConfig;
   toolId?: string;
   arguments?: Record<string, unknown>;
   resultAssignments?: Record<string, string>;
@@ -142,6 +145,8 @@ export type WorkflowGraph = {
     knowledgeMode: "automatic" | "on_demand";
     knowledgeTopN: number;
     knowledgeScoreThreshold: number;
+    enableInterrupt: boolean;
+    turnConfig: TurnConfig;
   };
   nodes: Array<{
     id: string;
@@ -172,6 +177,8 @@ export function defaultGraph(): WorkflowGraph {
       knowledgeMode: "automatic",
       knowledgeTopN: 5,
       knowledgeScoreThreshold: 0,
+      enableInterrupt: true,
+      turnConfig: defaultTurnConfig(),
     },
     nodes: [
       {