Struct EnvContribution 

pub struct EnvContribution<'a> {
    pub from_host: &'a BTreeMap<EnvVarName, Option<String>>,
    pub overrides: &'a BTreeMap<EnvVarName, String>,
}

Resolved environment contribution (CACHE-008).

from_host carries each allow-listed variable name together with the value it took in the host process at key-derivation time, or None when the host did not set that name. The cache does NOT consult std::env itself: callers resolve the values (typically std::env::var(name).ok()) and hand the map here.

overrides carries the task-level env.override map. On a name appearing in both maps, the overrides entry wins: the from_host entry for that name does NOT contribute to the key. Enforcement happens inside contribute_env, so the caller MAY leave the from_host map as-passed.

Fields

from_host: &'a BTreeMap<EnvVarName, Option<String>>

Allow-listed host variable names paired with their values at key-derivation time (None for absent).

overrides: &'a BTreeMap<EnvVarName, String>

Task-level hardcoded name/value overrides.