GuestRegion
A guest-controlled window [ptr, ptr + len) of WASM linear memory, decoded from a packed warp_run result by unpackWarpResult.
Both words are unsigned 32-bit values carried as non-negative Longs (0..0xFFFF_FFFF). They must never be narrowed to a signed Int before bounds validation: a value with bit 31 set would wrap negative, slip past a naive bounds check, and index host memory (a sandbox escape) or hit ByteArray(negative) (a raw exception escaping WasmException).