Run fails if input buffer is only partially read

[naegelejd]

It is possible to write a codespec that only partially reads from an input buffer, causing the run to fail, even if the job returns exit code 0.

Example: Copy stdin to stdout up to a maximum number of bytes, then exit successfully.

It is not required that a codespec read its input buffers. However, once the codespec begins reading from stdin or a named input pipe, should it be required to read that stream until EOF? If so, we'll document it. If not, then perhaps we need to change the logic to allow partial reads, and respect the return code of the main container.