Function parse_idle_timeout_secs 

pub fn parse_idle_timeout_secs(raw: Option<String>) -> IdleTimeoutSetting

Resolve a raw idle-timeout override into the value actually in force.

Pure — no environment access — so it is unit-testable directly rather than by mutating process-global env. That shape is copied from devflow-cli’s four parse_* timeout readers; their BEHAVIOUR is deliberately not copied, because none of them clamps against a floor and none logs when a fallback engages. There is no clamp-and-log precedent anywhere in this workspace; this is the first (D-04).