Show output of cached build steps

Sometimes the build steps break without any exit code. The image layers linked to these steps are then cached and used for other unsuspecting builds.

We can debug the issue with the original build using the output/error. The builds that use the cache, however, can't be debugged.

Fix this by copying the output/error from the deploy candidate that originally built the cached layer.


The issue names no files or tests; start by tracing cached build-step handling and the deploy candidate data that stores output and errors. Confirm how cached layers are reused, then verify that builds using them display the original deploy candidate's output/error.

Written by the indexing model from the issue text.