This repository is a small reproducible example of a fundamental issue with boa and the Internet Computer's futures implementation.
The canister code is found in canisters/boa/src/lib.rs. There are comments explaining the problem.
To test your solution simply start an IC replica and then run ./test.sh from a terminal. You may need to run chmod +x test.sh to enable executing test.sh as a script.
Running test.sh will simply deploy the canister locally and call the rand_bytes update function. By default the function should return the string "1,2,3". You will need to follow the comments to enable the code that is broken.
If you can get the broken code to work, then you are a hero. It's as simple as that.