D578 - Random devices serve a deterministic stream

Status: decided Date: 2026-09-07

/dev/random and /dev/urandom are one non-blocking device reading from orbistoun_core::entropy, a fixed sequence shared with every other randomness source; a write to it is refused. Recording successful opens is a setting, ORBISTOUN_TRACE_OPENS, off by default.

Why: a random device's bytes carry no meaning, so it can be served without inventing a layout or vendor semantics, and FreeBSD makes both names one device. Every measurement here rests on two runs behaving identically, and a physically random seed sends the guest down a different path each run. One pool keeps two readers from drifting apart. A write stirs nothing in a fixed sequence, so accepting it would claim an effect. Recording opens changes only what is reported, so it carries no caveat, and it is gated because successes are frequent.

Rejected:

• Host randomness: two runs of one build stop being comparable.
• Leaving the devices absent: they carry no semantics that could be answered wrongly.
• Always recording opens: a lock and a string per open changes what it observes.