fix(hub-client): add onKeyDown guard for async Automerge change events

[shikokuchuo]

Fixes #35. Follow-up to #100.

Bug

Automerge-repo's message pipeline has await boundaries between the WebSocket message and the DocHandle change event. The immediate callback from #102 fires in a later microtask, which usually drains before the next keystroke — but not always. In the rare case where a keystroke macrotask fires first, Monaco is still stale and characters land at wrong positions.

Fix

Add an editor.onKeyDown guard that syncs Monaco with Automerge before the keystroke is processed. A pendingRemoteSync dirty flag (set only for remote changes via an isApplyingLocal guard) ensures the expensive getValue() + diff only runs when a remote change is actually pending. Solo typing costs one boolean check per keystroke.

[cscheid]

Thanks! I'll reiterate what I said at Asilomar, which is that we have plenty of time to redesign the monaco editor component. It might be a good idea to do so now that we have a better handle of the properties we need the system to hold.

[shikokuchuo]

What seemed like an easy fix (originally in #100) appears to be really hard to pin down. The changes here are not sufficient. We probably should be looking more holistically at the integration.

[cscheid]

Following up a bit more. Have you investigated the automerge history to see if, like our high latency problems, there's a permanent record of the bug on the document? If that's the case, then we might be able to combine this with additional logging to get at a root cause.

[shikokuchuo]

It's the Monaco side - the keystroke is getting lost without ever hitting the Automerge document. I need to look at greater depth into Monaco.