fix: resolve Zod v4 compatibility issue in delegate_task tool schema (#590)

Author: omeraplak

.changeset/khaki-islands-try.md

@@ -0,0 +1,15 @@
+---
+"@voltagent/core": patch
+---
+
+fix: resolve Zod v4 compatibility issue in delegate_task tool schema
+
+Fixed a compatibility issue where `z.record(z.unknown())` in the delegate_task tool's context parameter was causing JSON schema generation errors with Zod v4. Changed to `z.record(z.string(), z.any())` which works correctly with both Zod v3 and v4.
+
+The error occurred when using the MCP server or other components that convert Zod schemas to JSON schemas:
+
+```
+TypeError: Cannot read properties of undefined (reading '_zod')
+```
+
+This fix ensures the delegate_task tool works seamlessly across all Zod versions supported by the framework (^3.25.0 || ^4.0.0).

packages/core/src/agent/subagent/index.ts

@@ -705,7 +705,10 @@ ${task}\n\nContext: ${safeStringify(contextObj, { indentation: 2 })}`;
       parameters: z.object({
         task: z.string().describe("The task to delegate"),
         targetAgents: z.array(z.string()).describe("List of agent names to delegate the task to"),
-        context: z.record(z.unknown()).optional().describe("Additional context for the task"),
+        context: z
+          .record(z.string(), z.any())
+          .optional()
+          .describe("Additional context for the task"),
       }),
       execute: async ({ task, targetAgents, context = {} }, currentOperationContext) => {
         // Fall back to the original operation context if not available