Validate a user-supplied _meta key for attachment: it MUST be a
well-formed key (isValidMetaKey) and MUST NOT use an MCP-reserved prefix
(isReservedMetaPrefix). Returns true if the key is safe to use. Uses the
2025-11-25 / draft "second label" reserved-prefix rule; pass a
ProtocolVersion to apply the rule for a specific connection.
Validate a user-supplied _meta key for attachment: it MUST be a well-formed key (isValidMetaKey) and MUST NOT use an MCP-reserved prefix (isReservedMetaPrefix). Returns true if the key is safe to use. Uses the 2025-11-25 / draft "second label" reserved-prefix rule; pass a ProtocolVersion to apply the rule for a specific connection.