Fail workflows when agents report incomplete

[Copilot]

A successful agent process could emit report_incomplete while leaving the Actions job green. Failure-issue reporting could run or fail independently without propagating the incomplete state to the job conclusion.

• Failure propagation

  • Call core.setFailed() when a meaningful report_incomplete signal is detected.
  • Continue optional issue reporting after marking the step failed.
  • Preserve the exception for task-completion registration-only reports.

• Regression coverage

  • Cover successful agent exits that report incomplete.
  • Verify the step remains failed when issue reporting is disabled or issue creation fails.

core.setFailed("Agent reported that it could not complete the task");

• Fixes report_incomplete leaves workflow green when the agent exits 0 #59274