ubuntu-app-test fails to launch apps at all [CRITICAL **: Unable to get PID for 'ubuntu-app-test' application]

If it's relevant, I launch everything and do all development from an ssh login. Until recently ubuntu-app-launch worked fine in this configuration (bug 1654915).

Status changed to 'Confirmed' because the bug affects multiple users.

This WFM with this silo: https://bileto.ubuntu.com/#/ticket/2577

It was probably the trusted overlay prompts not being ported to systemd, so you were fighting a Upstart/Systemd battle that would only end in tears.

The silo does not help for me. Mir applications fail to connect, but not with the error described in this bug. Instead I get various errors about being unable to connect to the Mir server, which vary depending on the test client used.

Further investigation shows connections to the Mir server are failing with the error "Error processing request: Invalid prompt session" when the proxy socket is used, but if the regular MIR_SOCKET value is forced the connection succeeds.

I had to use strace to glean the actual connection failure message since it gets swallowed somewhere in the Mir client.

I was able to hit this issue when U8 crashed while ubuntu-app-test was open. Leaving behind in:
/run/user/1000/systemd/transient/ubuntu-app-launch-application-legacy-ubuntu-app-test-.service

Once this was stuck there even relogging seems to be causing this issue. If you remove that file then it works again.

To reproduce this issue:
1) In U8 on a terminal start ubuntu-app-test with any application
2) Copy the /run/user/1000/systemd/transient/ubuntu-app-launch-application-legacy-ubuntu-app-test-.service somewhere
3) Relog into U8
4) Copy the *.service file back into /run/user/1000/systemd/transient/
5) Try to use ubuntu-app-test again from a terminal in U8

Then you'll hit this error.

An actual way to reproduce:

1) Start ubuntu-app-test through a terminal on U8
2) sudo kill -9 <unity8-pid>
3) Try to start ubuntu-app-test

Error, and you'll see that *.service file is there