mcp: validation only for accept action (#766)

Fix: #758

- validate schema only for accept action
- add unit test

mcp/client.go

@@ -590,7 +590,7 @@ func (c *Client) elicit(ctx context.Context, req *ElicitRequest) (*ElicitResult,
 			return nil, err
 		}
 		// Validate elicitation result content against requested schema.
-		if schema != nil && res.Content != nil {
+		if res.Action == "accept" && schema != nil && res.Content != nil {
 			resolved, err := schema.Resolve(nil)
 			if err != nil {
 				return nil, &jsonrpc.Error{Code: jsonrpc.CodeInvalidParams, Message: fmt.Sprintf("failed to resolve requested schema: %v", err)}