Indeed, this is close to what Yjs (popular CRDT library) does: each client instance (~ browser tab) chooses a random 32-bit clientId, and character IDs combine this clientId with local counters. https://github.com/yjs/yjs/blob/987c9ebb5ad0a2a89a0230f3a0c6...

Any given collaborative document will probably only see ~1k clientIds in its lifetime, so the odds of a collision are fairly low, though I'd be more comfortable with a 64-bit ID.