Client-side sampling validation doesn't use CreateMessageResultWithToolsSchema when tools are present #1346

Describe the bug
When a client handles a sampling/createMessage request that includes tools, the client SDK validates the handler's response using CreateMessageResultSchema instead of CreateMessageResultWithToolsSchema. This causes valid tool_use responses (which have array content) to be rejected with a validation error.

The server-side was fixed in PR #1156, but it appears that the client-side validation in Client.setRequestHandler was missed.

To Reproduce

1. Create a client that declares sampling: { tools: {} } capability
2. Set up a sampling handler that returns tool_use content when the LLM wants to use tools
3. Connect to a server that sends a sampling/createMessage request with tools
4. When the LLM responds with tool_use, the client rejects the response with validation error

Expected behavior
When params.tools is present and non-empty in the sampling request, the client should validate the response using CreateMessageResultWithToolsSchema (which accepts array content with tool_use blocks) instead of CreateMessageResultSchema (which only accepts single object content).

Logs

[Sampling] Server requested LLM completion with 2 tools
[Sampling] LLM requested 1 tool(s): add
{
  "content": [
    {
      "type": "text",
      "text": "MCP error -32602: MCP error -32602: Invalid sampling result: [\n  {\n    \"code\": \"invalid_type\",\n    \"expected\": \"object\",\n    \"path\": [\n      \"content\"\n    ],\n    \"message\": \"Invalid input: expected object, received array\"\n  }\n]"
    }
  ],
  "isError": true
}

Additional context

Location of bug: packages/client/src/client/client.ts lines 461-469

Current code (SDK 1.25.1):

// For non-task requests, validate against CreateMessageResultSchema
const validationResult = safeParse(CreateMessageResultSchema, result);
if (!validationResult.success) {
    const errorMessage = validationResult.error instanceof Error ? validationResult.error.message : String(validationResult.error);
    throw new McpError(ErrorCode.InvalidParams, `Invalid sampling result: ${errorMessage}`);
}
return validationResult.data;

Suggested fix:

// For non-task requests, validate against appropriate schema
// Use CreateMessageResultWithToolsSchema when tools are present (allows array content with tool_use)
const hasTools = params.tools && params.tools.length > 0;
const resultSchema = hasTools ? CreateMessageResultWithToolsSchema : CreateMessageResultSchema;
const validationResult = safeParse(resultSchema, result);
if (!validationResult.success) {
    const errorMessage = validationResult.error instanceof Error ? validationResult.error.message : String(validationResult.error);
    throw new McpError(ErrorCode.InvalidParams, `Invalid sampling result: ${errorMessage}`);
}
return validationResult.data;

Also requires adding CreateMessageResultWithToolsSchema to the imports at the top of the file.

(Issue created by Claude and edited by me)