Function capture 

pub fn capture(
    writer: Option<&SnapshotWriter>,
    slot: &str,
    exec_id: u64,
    subject_kind: &str,
    subject_id: &str,
    readout_name: &str,
    lod: &str,
    rendered: &str,
)

Capture a rendered body to the snapshot store. Best- effort: a None writer (snapshots disabled), lock poisoning, or “sqlite init failed” (inner Option is None) all collapse to silent no-ops — snapshot capture must never block or corrupt the readout-fire path.

subject_id is normally produced by ReadoutContext::subject_id — the trait default folds subject_name + subject_labels into the conventional name@labels shape; session-scoped contexts override to a literal "session".