This is fixed for 8.1.19/the next nightly build.
This is "fixed" for 8.1.19/the next nightly; you will no longer get an incorrect autocompletion for the (builtin) format
method that looks like it's a string instance autocompletion. You will not get string instance autocompletion, unfortunately, but smarter 'local' autocompletion is probably the next item I'd like to address.
The inner problem that causes this is now caught, so if the fold parsing logic breaks, you won't get any folds, but everything else will still work. A fix for the fold parsing logic will hopefully come soon.
And yes, project library autocompletion throughout the designer.
As a small bonus convenience feature, we also added an option to select which hint scope to provide for autocompletion while authoring project library scripts:
This setting will persist with your script library, but does not affect actual execution in any way; it's just a convenience to help with script authoring.