Function parse_agent_definition 

pub fn parse_agent_definition(
    directory_id: &str,
    contents: &str,
) -> Result<Option<Personality>, PersonalityParseError>

Parses one .agents agent definition.

directory_id is used when the optional frontmatter id is absent. Disabled definitions return Ok(None) so callers can omit them without treating intentional configuration as a parse failure.

Errors

Returns PersonalityParseError when frontmatter is malformed or a required name, description, directory fallback ID, or prompt is missing.