dustRestoreGate

Optional restore gate awaited ONCE before the first dust sync that finds no local checkpoint (a fresh install / new device / new network). The host's chance to obtain Drive consent so the cloud-checkpoint restore can succeed instead of the sync silently replaying from genesis. The SDK hands the gate the restored RestoredAppState (prefs + host payload, null when nothing is in the cloud) — the gate can fire during build, before the host holds any SDK handle, so it can't fetch that itself. Must resolve promptly (grant, decline, or nothing-to-do) and must NOT call back into wallet sync APIs (it runs inside the dust-sync critical section). Omit it (the default) and behavior is unchanged. Registered as a builder option — not a post-build property — because the proactive dust sync starts at build time and would otherwise race past the gate into genesis.