Function optional_ttl 

pub fn optional_ttl(
    config: &HashMap<String, Value>,
    node_type: &str,
) -> Result<Option<u64>, String>

Parses the optional ttl_seconds. Absent means no expiry; 0 is rejected.

store-get (Task 2, the first caller of this module) had no use for a TTL – reading a key never sets one – so this was test-only for a while. store-set now calls it unconditionally from from_config, same as required_template: this is pure config validation with no dependency on a store actually being reachable, so unlike resolve it needs no redis-store-gated pair – one definition, always compiled, matches how it is called on every feature combination.