When an AI Agent Joins Your Yjs Room, Three Assumptions Break

Wiring an LLM as a first-class Yjs peer is architecturally sound — but it invalidates three silent assumptions your collaboration stack already makes about peer symmetry: throughput, undo ownership, and presence cadence. You've tuned a Yjs provider under real collaborative load. You know the feeling before you can name it — one heavy client starts lagging the room, presence updates stutter, and you end up adding a debounce somewhere and calling it done. Now imagine that client generates text at 3,000 words per minute, never goes offline, and has its own awareness cursor. That's not a sidebar feature. That's a new class of peer, and your collaboration architecture wasn't designed for it. The Demo Is Real — But It Skips the Hard Parts In April 2026, a working demo wired an LLM as a genuine server-side Yjs document peer — same transport as the human editors, same CRDT, its own awareness state. The implementation uses y-prosemirror and the standard awareness protocol directly. If you've shipped TipTap collaboration, you already have every dependency it needs. The architecture is correct. Making the agent a server-side peer — rather than a client-side bolt-on posting diffs over a REST endpoint — gives you one convergence model instead of two, real presence semantics for the agent, and a clean separation between the LLM streaming layer and the document state layer. But the demo establishes the peer model. It doesn't stress-test what happens to your existing assumptions once that peer is running. The Silent Assumption Every CRDT Implementation Makes Here it is — the assumption baked into the Yjs awareness protocol, the undo manager, and your backpressure strategy, the one nobody wrote down because it was always true until now: All peers produce operations at roughly human speed. Not identical speed. Human typists vary. But they land in the same order of magnitude. The entire design space — how often you broadcast awareness, how you scope undo history, whether you need per-