Possible race conditions when compiling and running

I'm seeing this in logs for `/compile` requests:

A web handler threw an exception. Details:
data/haskell/build/Pxx/Pxxxxxxxxxxxxxxxxxxxxxx.basever: openFile: does not exist (No such file or directory)

This indicates that some part of the system thinks the build is done, but there's no basever file. I'm not sure how that could happen. Maybe a race condition of some kind?

I also see this for `/runMsg`:

A web handler threw an exception. Details:
data/haskell/build/Pxx/Pxxxxxxxxxxxxxxxxxxxxxx.err.txt: getFileStatus: does not exist (No such file or directory)

Similar situation: the system thinks that the build is complete, but there's no build output file, which should always be created as part of a build.

Empieza rastreando los manejadores web `/compile` y `/runMsg` y cómo determinan que una compilación ha terminado. Examina el tratamiento de los archivos `basever` y `.err.txt` que faltan en `data/haskell/build/`. Se considera terminado cuando se entiende la condición de carrera y estas solicitudes ya no informan de que faltan artefactos de compilación.

Escrito por el modelo de indexación a partir del texto del issue.