In toaster-next, I occasionally see errors which take this form:

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NOTE: Logging error 2: {'build': <Build: 2 Project object core-image-minimal>, 'message': 'An uncaught exception occured in runqueue', 'pathname': '/home/ell/dev/toaster/poky/bitbake/lib/bb/runqueue.py', 'level': 2, 'lineno': 1223}
ERROR: An uncaught exception occured in runqueue
Traceback (most recent call last):
  File "/home/ell/dev/toaster/poky/bitbake/lib/bb/runqueue.py", line 1210, in RunQueue.execute_runqueue():
             try:
    >            return self._execute_runqueue()
             except bb.runqueue.TaskFailure:
  File "/home/ell/dev/toaster/poky/bitbake/lib/bb/runqueue.py", line 1144, in RunQueue._execute_runqueue():
                     # needs it
    >                depgraph = self.cooker.buildDependTree(self, self.rqdata.taskData)
                     self.rqdata.init_progress_reporter.next_stage()
  File "/home/ell/dev/toaster/poky/bitbake/lib/bb/cooker.py", line 741, in BBCooker.buildDependTree(rq=<bb.runqueue.RunQueue object at 0x7f049d83c4a8>, taskdata=<bb.taskdata.TaskData object at 0x7f049f786dd8>):
                     for ei in extra_info:
    >                    depend_tree["pn"][pn][ei] = vars(self.recipecache)[ei][fn]
     
KeyError: '/home/ell/dev/toaster/poky/meta/recipes-devtools/run-postinsts/run-postinsts_1.0.bb'
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While this looks like a bitbake error, it also causes the corresponding Toaster build to "hang": the most recent builds area doesn't update.

We may not be able to fix the bitbake error or even reproduce it reliably, but we can detect when exceptions occur at this point in the bitbake run and capture them properly in Toaster, so the build at least fails (and is reported as failed in the UI).