Bug: scatterplot column autocomplete is broken

[breck7]

repro steps:

1. go to ohayo.computer
2. create reddit template
3. in source editor, change line 9 scatter xColumn

expected:
correct column names suggested in autocomplete

actual:

[breck7]

The issue is around runtime autocomplete. Also involving the fact that we may be creating a new version of the program in the editor, that hasn't executed yet, so in some cases the autocomplete may be depending on things that aren't there yet.

Need to figure out the general pattern here.