Overview

• Adds comment syncing to the push process

Implementation approach and notes

• Uses websockets bi-directional channel interactive sync process
• Adds a lot of websocket utilities which are also useful to SyncV3 :)
• UCM scans the full causal history and collects comment hashes, sends them to the server, the server reports back which hashes its missing, which UCM then uploads.

Interesting/controversial decisions

The algorithm here is pretty naive, the "correct" way to sync something like this is to make comments part of the main causal merkle-tree (and affect hashing); but a redo of code hashing is out-of-scope;

There are smarter ways to do this sync even without integrating comments into the history;
one particular option would be to tag each branch with not just its causal root, but also the root of a Merkle Search Tree which contains all the comments it knows about which are reachable from that causal root. MSTs are a useful data type for efficiently doing unions of arbitrary sets across distributed clients like this.

Since most cases are likely to be small here, we'll ship with this simple version in the hopes it lasts us for a while, and we can integrate the more complex and efficient version later.

Comment sync is quite likely to be dwarfed by code-sync in the majority of cases.

Test coverage

• Manual testing
• Transcripts on the Share side.