feat: implement AfterTool tail tool calls (#18486)

packages/core/src/tools/tools.ts

@@ -579,6 +579,15 @@ export interface ToolResult {
    * Optional data payload for passing structured information back to the caller.
    */
   data?: Record<string, unknown>;
+
+  /**
+   * Optional request to execute another tool immediately after this one.
+   * The result of this tail call will replace the original tool's response.
+   */
+  tailToolCallRequest?: {
+    name: string;
+    args: Record<string, unknown>;
+  };
 }
 
 /**