Optional result-level _meta object. Reserved by MCP on every Result (the base interface all paginated list results extend), so it round-trips on every protocol version: toJson emits it only when set and fromJson parses it. Unset by default, so pre-existing wire output is unchanged.
Draft CacheableResult freshness hint (ttlMs/cacheScope). Round-trips symmetrically: toJson emits it when set and fromJson parses it. The server sets this (draft-gated) so pre-draft wire output is unchanged.
optional _meta object
Result of resources/templates/list.