ReadonlychannelThe channel this spare backs up.
Optional ReadonlydisplacedThe DISPLACED PRIMARY — the endpoint set the channel was fed from at the moment the swap landed, which the reverse gesture restores. Present exactly while the latch is held, so a show that restarts mid-swap comes back mid-swap: the session's patch capture brings the channel back on the spare, and this brings back what to return it to.
ABSENT means the latch is released, not "an empty primary" — a channel swapped while
unpatched holds [], which is a different fact and restores to unpatched.
Optional ReadonlydisplacedThe REGISTERED SOURCE the displaced primary referenced, when it had one — restored by the reverse gesture so a channel that followed a source's head-amp goes on following it. Meaningful only while displaced is present; absent means the primary was a raw port patch, which is the ordinary case.
Optional ReadonlylabelOptional operator label for the spare ("DI B", "SM58 spare").
ReadonlysourceThe spare source's left/mono port name (persistence-by-name).
Optional ReadonlysourceThe spare source's right port name, for a stereo spare.
A pre-declared spare for a channel, and the SWAP LATCH over it: if the primary mic/DI dies mid-show, one tap re-points the strip onto the spare input and REMEMBERS what it displaced, so the reverse is one tap too (
2026-07-30-southbound-actuator-contract.md§10a). The spare is named by the source endpoint the engine should patch (persistence-by-name).Neither the preamp nor the alignment follows the swap: head-amp is a property of the physical port and a spare is PREPARED (§10b), and the align delay described the dead mic's position in the room (§10c). This shape therefore carries the wiring and nothing else.