The effect backends

Five kinds of thing an effect is made of, each behind one contract the runtime leases, re-seats and re-fires.

geometry's transform takes either { position, rotation, scale } or the ribbon form { from, to, width } — a strip stretched between two world points, which is what a beam, a trail and a tether all are.

material records the mesh's own material before it stamps and puts it back when the play ends.

feature writes its params into featureParams(identity), which the render feature reads each frame. A render feature is compiled as its own chunk, so that table is the channel between a play and the pass it drives; active says whether any play currently holds it.

There is one entry per feature identity, so two plays through the same feature share it: the newest one's parameters are what the pass reads, and active stays true until the last of them lets go.

The contract

{
    key(spec) -> string,          -- the pool bucket; same key = interchangeable
    acquire(spec) -> instance,    -- the only member that allocates
    seat(instance, spec),         -- re-tune and re-position one the pool holds
    start(instance),              -- begin
    stop(instance),               -- stop producing; what is drawing finishes
    quiet(instance),              -- stop and remove now
    place(instance, position),    -- retarget
    bytes(instance) -> number,    -- GPU bytes it holds
    active(instance) -> boolean,  -- still drawing after it stopped producing
    silence(instance) -> (reason?, detail?),
    free(instance),               -- reached only by an explicit drain
}

A family that needs a way of drawing this module does not ship registers one with effects.registerBackend(kind, backend) rather than widening the runtime.