Function parse_entity_option_key 

pub fn parse_entity_option_key(key: &str) -> Option<(&str, EntityRole)>

Parses a well-formed entity-identity option key of the shape greptime.semantic.entity.<type>.{id|descriptive|scope} into (entity_type, role). The <type> may itself contain dots; the role is the final dot-separated segment. This is the single parser of the key format — DDL validation and the read-time derivation both go through it.