Plugins that let you read the value of a process variable in SAIL

You can directly use pv!variableName inside your SAIL code but process variable and UI task needs to be in same process model .. not sure if i understood your question correctly

@nickh Unfortunately you couldn't read the returned data using startprocesswrite as it's of type fire and forget. Probably you could go with either of the approaches as specified below:
>> Save the details into database using the process which you trigger by using startprocesswrite and read the values from the database in the SAIL interface.
>> Make use of the queryProcessAnalytics or getportalreportdatasubset and query the process analytics of the process triggered using startprocesswrite.

But please bear in mind that you need to identify the right record and for this you may have to identify unique attributes that fetches you a right record in any case.

Further I can also confirm that there aren't any OOTB or shared component available for doing the above.

@nick: You can create expression function to get the process variable value from particular process. copy existing code of Get external PV smart service.(Not recommended if you are on cloud )