extensions property
Extensions framework (MCP 2026-07-28). Keys are reverse-DNS extension
identifiers (e.g. io.modelcontextprotocol/tasks, following the _meta
key naming rules with a mandatory prefix); values are per-extension
settings objects (an empty object = supported with no settings).
Advertised via server/discover / initialize capabilities.extensions.
Additive — absent/empty for peers that do not use extensions.
Implementation
final Map<String, Map<String, dynamic>>? extensions;