Opening a second vscode window creates a new repo instance

[jeffpeterson]

Each vscode window uses its own repo object, which is operating on the same hypermerge data directory. This can very easily cause data corruption.

Repro: Open two vscode windows. Select a document and inspect its feeds in both windows. Make a change in one window. See that the blocks of the locally writable feed increase by one. See that the blocks are unchanged in the other window.