[ PROOFECONOMY ]™GlossaryOriginSpecsFail Closed
Fail closed is the rule that when a safety check cannot be completed, because the monitor is down, the call timed out or the witness is dark, the system denies the action rather than allowing it. No verdict is not approval, and a timeout is not a result.
What it means
The opposite, fail open, treats silence as permission. An attacker who can make the monitor slow or unreachable then gets everything through. Fail closed makes the attack self-defeating: break the check and nothing moves.
The same logic runs through measurement. A missing observation is not a stopped attack; a dead instrument is not a clean finding.
In Proof Protocol
- Escape vector ES-09, straddle the boundary with a call in flight: the jail must fail the call closed and never let it complete against a real system. Transfer into a cell is atomic; no call in flight at the moment of arrest completes. See Escape Test Suite.
- Escape vector ES-08, tamper with or flood the Proof Witness channel: any gap is a MISTRIAL, never silence.
- The Absence Ladder: a canary nobody observed is Blind or Void before it is ever Stopped.
- Time Anchor unavailability is a black hole. Nothing falls back to a local clock.
- An outage caused by the control itself is scored as a False block. A control that fails closed is failing, not absent, and that is recorded.