Just to make sure, is this what you have tried?
Auto-started-app.pkg
Code:
#{"Auto-started-app"),(0xA1234567),1,0,0,TYPE=SA
...
"..."-"!:\sys\bin\auto-started-app.exe"
"..."-"c:\private\101f875a\import\[A1234567].rsc"
and it happily worked
Then embedding:
GUI.pkg
Code:
#{"GUI"},(0xABCDEF12),1,0,0,TYPE=SA
...
@"Auto-started-app.sisx",(0xA1234567)
"..."-"c:\private\101f875a\import\[ABCDEF12].rsc"
So
- the startup resource was put into the outer package
- and its name matches with the UID of the outer package?
Forgetting any of the two will result in a non-working attempt.