it seems there is no error any more, because my code returns :
"/data/user/0/edu.mit.appinventor.aicompanion3/cache/temp.png" with companion
or "/data/user/0/appinventor.ai_jm_latour.imagesMp3/cache/temp.png" with built
but i don't really know if temp.png exists, because i can't go there and see it with my file explorer, and i can't use it in AI with blocks to display image file:
I also try to get it with "temp.png", "/temp.png", "//temp.png" but none of them display image file...
