We should have a hook that's called on "serial connection ended"

[obra]

It doesn't matter what kind of serial connection drop it is, but if the device detects the port being closed, it should be called.

then focus can listen for it and reset its own state.

[tlyu]

I think we probably do want something like that kind of functionality. One thing to think about is that a lot of the higher-level parsing happens in the actual plugins that use Focus, which don't really have a central way of resetting their parse state.

One possibility is to introduce some kind of EOF indication, which would function like EOL currently does. It would terminate the current item's parse. This might produce some invalid inputs as a side effect, but probably harmless ones.

Flushing input is a bit tricky: CDC serial doesn't support it (uses the flush method to flush output instead), and if the event is switching to a different host connection, it might not be possible to flush the input from the other connection.

Having this hook activate on DTR drop for CDC serial might help with some situations where some program decides to do active probes of all available serial devices on the host.