Refactor workflow agent and routing components for improved functionality

- Introduce WorkflowAgentStage to manage agent stage configurations and enhance interaction with the workflow engine.
- Implement WorkflowEdgeEvaluator for priority-aware edge evaluation, improving routing decisions based on conditions and user turns.
- Update WorkflowBrain to handle user turns and routing more effectively, ensuring agents cannot have only one default path.
- Enhance CallEndCoordinator to track speech events and manage call termination based on queued speech.
- Add new models and output handling for workflow interactions, improving clarity and maintainability.
- Update tests to validate the new routing logic and agent behavior under various scenarios.

frontend/src/components/workflow/panels/EdgeSettingsPanel.tsx

@@ -27,10 +27,14 @@ import type { ExpressionRule, WorkflowEdgeData } from "../specs";
 
 export function EdgeSettingsPanel({
   edge,
+  sourceType,
+  isOnlyOutgoing,
   hasOtherDefaultPath,
   onChange,
 }: {
   edge: Edge;
+  sourceType?: string;
+  isOnlyOutgoing: boolean;
   hasOtherDefaultPath: boolean;
   onChange: (patch: WorkflowEdgeData) => void;
 }) {
@@ -109,7 +113,10 @@ export function EdgeSettingsPanel({
             {
               value: "always",
               label: "默认路径",
-              disabled: mode !== "always" && hasOtherDefaultPath,
+              disabled:
+                mode !== "always" &&
+                (hasOtherDefaultPath ||
+                  (sourceType === "agent" && isOnlyOutgoing)),
             },
             { value: "llm", label: "大模型判断" },
             { value: "expression", label: "表达式" },
@@ -127,24 +134,31 @@ export function EdgeSettingsPanel({
             当前节点已经有一条默认路径；其它出边需要使用大模型判断或表达式。
           </span>
         )}
-        <label className="block">
-          <div className="mb-1.5 text-sm font-medium text-foreground">
-            优先级
-          </div>
-          <Input
-            type="number"
-            value={priority}
-            onChange={(event) => {
-              const nextPriority = Number(event.target.value) || 0;
-              setPriority(nextPriority);
-              publish({ nextPriority });
-            }}
-            className="border-hairline-strong bg-background text-foreground"
-          />
-          <span className="mt-1.5 block text-xs text-muted-foreground">
-            条件路径按数字从小到大判断，默认路径始终作为兜底。
+        {sourceType === "agent" && isOnlyOutgoing && mode === "always" && (
+          <span className="-mt-1 block text-xs text-destructive">
+            Agent 不能只有默认路径；请改为条件路径，或删除连接以持续对话。
           </span>
-        </label>
+        )}
+        {mode !== "always" && (
+          <label className="block">
+            <div className="mb-1.5 text-sm font-medium text-foreground">
+              优先级
+            </div>
+            <Input
+              type="number"
+              value={priority}
+              onChange={(event) => {
+                const nextPriority = Number(event.target.value) || 0;
+                setPriority(nextPriority);
+                publish({ nextPriority });
+              }}
+              className="border-hairline-strong bg-background text-foreground"
+            />
+            <span className="mt-1.5 block text-xs text-muted-foreground">
+              条件路径按数字从小到大判断；默认路径不参与优先级。
+            </span>
+          </label>
+        )}
       </SectionCard>
 
       <SectionCard