buildkite-bootstrap-issue

Steps to reproduce:

1. Configure a Buildkite pipeline to build this repository using pipeline.yml.
2. Start an agent by running BUILDKITE_AGENT_TOKEN=<xyz> ./start-bootstrapped-agent.sh
3. Trigger a new build of the pipeline
4. After the command has been running for 10 seconds, click Cancel button for the step
5. Observe that job output ends with line Received cancellation signal, interrupting
   • expected to see lines:

   Terminated
   🚨 Error: The command was interrupted by a signal
   2021-09-03 16:43:13 DEBUG  Terminating bootstrap after cancellation with terminated
   

6. Observe that agent logs include the error message:

   2021-09-03 22:05:04 DEBUG  bootstrapped-agent [Process] Sending signal SIGTERM to PGID: 22 
   2021-09-03 22:05:04 INFO   bootstrapped-agent Process with PID: 22 finished with Exit Status: -1, Signal: SIGTERM 
   2021-09-03 22:05:04 DEBUG  bootstrapped-agent [JobRunner] Routine that refreshes the job has finished 
   2021-09-03 22:05:04 DEBUG  bootstrapped-agent [Process] Waiting for routines to finish 
   2021-09-03 22:05:04 DEBUG  bootstrapped-agent [LineScanner] Encountered EOF 
   2021-09-03 22:05:04 DEBUG  bootstrapped-agent [JobRunner] Routine that processes the log has finished 
   2021-09-03 22:05:04 DEBUG  bootstrapped-agent [LineScanner] Finished 
   2021-09-03 22:05:04 ERROR  bootstrapped-agent [Process] PTY output copy failed with error: *errors.errorString: io: read/write on closed pipe
   

   • expected to see

   2021-09-03 22:03:12 INFO   default-agent Canceling job b5fc6588-c773-46a1-9398-359be603bee0 with a grace period of 10s 
   2021-09-03 22:03:12 DEBUG  default-agent [Process] Sending signal SIGTERM to PGID: 24 
   2021-09-03 22:03:12 DEBUG  default-agent [Process] PTY has finished being copied to the buffer 
   2021-09-03 22:03:12 INFO   default-agent Process with PID: 24 finished with Exit Status: 255, Signal: nil
   

Expected observations were determined by running the above steps, but using ./start-default-agent.sh to start the agent.