MCP servers are add-ons that give Claude Code extra tools. When a program drives Claude Code through the SDK and asks for something that needs an MCP server blocked by managed policy (settings an organisation deploys), Claude Code now refuses with the error code mcp_policy_blocked before it tries to connect. This covers:
mcp_togglemcp_reconnectmcp_authenticatemcp_read_resource
mcp_read_resource now also records why it failed, either a reserved address or a policy block, before it reports the error. Before, the only MCP error codes listed were mcp_client_registration_unavailable and mcp_redirect_uri_unusable.
The SDK documentation also now notes that deny and ask rules and hook matchers written as mcp__<connectorId> reach that server's tools as well.
A program can now tell a policy block apart from other MCP failures and show the right message, rather than treating it as a connection problem.