Hi Michael,
yes, I’d prefer a more private thread.
The build-wrapper.log is available together with build-wrapper-dump.json and compile_commands.json.
Of course I can provide a new process tree dump by triggering the build again.
Wrt. item 1 and “always hang”: the job containing this SonarCloud PoC is quite new … with out build number 7 we have been able to get everything up and running for the first time using build-wrapper. Now we are at build number 10. All of them have been hanging. But … “always” … hmmm … 
… strong word …
Wrt. item 2: this is our PoC project for qbs together with SonarCloud. So … “any qbs project” … hmmm … again a strong term … …
Wrt. item 3: yes, maybe I could replace qbs_processlauncher by some script containing the corr. strace call. Need to check what/where to change in our build infrastructure …
Wrt. item 4: inside the community here I’ve found a ticket
That one sounds like I run into other trouble with sonar-scanner when trying this. Or has this been fixed within sonar-scanner?
Of course I can also provide proc maps for the qbs_processlauncher process. And the corr. environ file.
And another idea is me writing a question to qbs mailing list asking whether others are using SonarCloud.