DAW/host parameter support is finished, including golden tests, etc. Everything works how I'd like it to.

The golden tests were slightly interesting. Since, obviously, a MIDI file can't contain host automation, it wasn't immediately obvious how to write golden tests for this. My first thought was just to hard-code a few automation events and do the tests that way. But what I came up with was a little config parameter that lets the golden tests request that specified MIDI continuous controller #s be translated to host automation inputs.

So, in Ableton, I created the test preset and set up some automations in two lanes. Once I got this working how I wanted, I copied and pasted the automation lanes into MIDI CC 1 and 2, and exported the MIDI file. Then in the golden tests, I mapped CC 1 to automation lane 0 and CC 2 to automation lane 1. The golden test produced exactly the output it was supposed to. This gives me a lot of flexibility in how to test this kind of thing.

Aside from finishing the host automation stuff, I tracked down and fixed a bug where undo/redo worked, but the right-hand side panel didn't update to reflect the changes from undo/redo unless you cleared the selection and re-selected the entities. This ended up being a nasty bug in the subscriptions code, which caused (a) some subscribers to see irrelevant changes, and (b) some subscribes to miss changes intended for them. Strictly speaking, #a was a problem with the subscriptions code, and #b was a misuse of the subscription API. But even the API misuse was because the API was bad. Both of these are fixed, and tested.