backgroundLifetimeMs

Ceiling on how long the decrypted seed may stay alive while the app is backgrounded. Backgrounding only soft-locks (UI gated, SDK kept alive for monitoring), so without this a seed could sit decrypted in memory indefinitely on a device whose screen never turns off. When the ceiling elapses it routes through the hold-aware lock — so an in-flight operation or a backgrounded Kicks match (which holds the session) DEFERS the wipe until it finishes, never gets torn out mid-flight; an idle, unheld session is wiped. Mutable so hosts can tune it.