While in a hybrid of "classic" and "modern" extensions, Generating Symbols is something that may have to be done quite regularly. Those unfamiliar with command line can find it cumbersome to use the generatesymbolreferences command.
While adding to VS Code (#1707) might be more complicated, can it be added as a menu item similar to "Build Server Application Objects"? That could even show progress, or allow you to build for just the highlighted objects....

After the initial run of
Finsql.exe command=generatesymbolreference
you can use the incremental symbol generation which is much faster and doesn't require any additional steps beyond compiling changed objects. To achieve it launch finsql with the flag generatesymbolreference=yes.
Would that address your scenario?
I wasn't aware that it needed to be launched with that parameter for incremental. Explains why it wasn't working.
It should be an option in the zup file/tools > options.
We'd always want it on; any consultants forgetting to turn it on would require a full rebuild?
Yes, it is good to do a full rebuild from time to time to make sure that the forgotten sessions are corrected.
We can look into adding it to the zup file, that's a good suggestion.
It simplifies things for those familiar with classic development environment.
Tools > Options seems to be the most appropriate.
Does it rebuild the symbol on compile? Or save?
I imagine Compile would be the best option here. In the scenario where an object was knowingly modified (but the user forgot to turn on incremental symbol building) they could correct the option and recompile the object to generate the symbol.
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I wasn't aware that it needed to be launched with that parameter for incremental. Explains why it wasn't working.
It should be an option in the zup file/tools > options.
We'd always want it on; any consultants forgetting to turn it on would require a full rebuild?