Novella where two vast digital civilizations simulate each other

Question

A couple of years ago, I came across an intriguing and fun novella about acorporeal civilizations (living as computer simulations) which I'd love to read again.

Can any of you identify which story I'm thinking of? Here is what I remember:

• By the time the events of the story unfold, the galaxy is populated by two civilizations, both existing as simulations on vast amounts of computronium. Biological life doesn't seem to exist anymore.
• Additionally, there is an expanding void, which destroys the computronium the two civilizations are running on, whose true nature is yet unknown.
• One of the two civilizations consists of lots of individuals which each have authority of what they want to do. The individuals have certain fixed roles, and when cloning themselves, for instance when embarking on a risky mission, the clones might recombine after meeting again or might not. I seem to recall that one of the roles was to be a "filter" (of information). The other civilization runs a concensus protocol including every bit of it, causing it to be quite slow in coming to decisions, but on other hand being more coherent.
• The two civilizations are fighting each other. Part of their war efforts include simulating the other kind, even in a nested fashion.
• I seem to recall that at some point, one of the civilizations discovers a way of detecting whether they live in a simulation.
• The ending is very nice.

The story was probably published on some blog or on a fan fiction hub. It is related in spirit to, but distinct from:

• Greg Egan's Diaspora, Permutation City or other stories of him set in the Amalgam/Aloof universe
• qntm's I don't know, Timmy, being God is a big responsibility
• Eliezer Yudkowsky's The Finale of the Ultimate Meta Mega Crossover

Answer 1

True Names by Cory Doctorow and Benjamin Rosenbaum. I read it in the anthology Fast Forward 2.

It is available on the Internet Archive here. It is described as:

the tale of duelling galactic colony-organisms that are competing to recruit all the matter in the universe for raw computation.

The main protagonist is Beebe, who is from the more individualistic simulation. The other simulation is called the Demiurge. They do indeed simulate each other looking for strategic advantage (Beebe narrating):

It has long been known that Beebe simulates Demiurge, and Demiurge simulates Beebe. We must build models of cognition in order to predict action—you recall my proof that competition between intelligences generates first-order empathy. But all our models of Demiurge have been outsidein theories, empirical predictive fictions. We have had no knowledge of (Her) implementation.

There are two filters, Alonzo and Algernon:

Alonzo was a filter. If Nadia was, under the veneer of free will and consciousness, a general-purpose strategy for allocation of intraBeebe resources, Alonzo was a set of rules for performing transformations on daemons—daemons like Nadia