- Any useful undocumented parameters?

NVRelayHaltTimerOnOn / NVRelayHaltTimerOnOff

Kills any existing timer (delayed message) when the trap is activated/deactivated.

- No equivalent of TrapFailChance for deactivation events?

The same fail chance applies to both activation and deactivation.  It can fail to send the trigger.

- TrapFailChance int or float?

Float.

- Do Failed activation attempts count toward the max activation counts?

They count towards the max trap activation count (NVRelayTrapCount), but not the max trigger activation count (NVRelayTrapTCount).

- Weighting scheme for weighted links could use more explanation.

Basically, it builds up a list of all the links, adding each link to the list the number of times specified in its weight.  It then picks a random link from that list.

- What is the default “inactive” value of the trapon/off/delay/max values?

NVRelayTrapOn="TurnOn"; NVRelayTrapOff="TurnOff"; NVRelayTrapTOn="TurnOn"; NVRelayTrapOff="TurnOff"; NVRelayTrapDelay=0; NVRelayTrapDelayMax=0; NVRelayTrapOnDelay=0; NVRelayTrapOnDelayMax=0; NVRelayTrapOffDelay=0; NVRelayTrapOffDelayMax=0

- NVRelayTrapExclusiveDelay: Do delayed messages queue up by default?

There can be multiple delayed messages waiting at the same time.  Normally, a delayed message should fire at that number of milliseconds after it was activated, regardless of other messages.

Note that I think I noticed a bug with ExclusiveDelay today - it doesn't work as expected if an object has multiple relay trap scripts on it which use delayed messages.  I suspect repeating won't work reliably either.
(e.g. values relating to timers and repeats are shared amongst all script instances, so an exclusive delay on one will kill timers on another.)

- Will NVRelayTrapRepeat use NVRelayTrapOn/OffDelay/Max params, or just the base generic delay?

It will use the most specific param specified.  The code is shared for all of this functionality, there are no separate code paths with more/less features.

1 for on, 0 for off.

can one relaytrap send signals to multiple objects? the guide suggests this is possible, but no idea how to separate the obj ids, tried a couple of things, but only the first object has received the activation message.

a swarm of relay traps it is then.

a destruction of an object should send a turnon signal to three other objects. no worries, working fine with three relay traps.

there can be, but as mentioned, no problem with using three relay traps.

just regular objects (it's a dml fix). I could link them I suppose, but hey, if it works, don't fix it..