diskspace not reporting corect values even though segments have been flushed to disk and are not in memory

diskspace not reporting corect values even though segments have been flushed to disk and are not in memory
the values allways show -1

Start by reproducing the reported diskspace behavior in Apache Pinot, focusing on the case where segments have been flushed to disk but the value remains -1. The issue provides no file, test, or entry point; done means identifying the cause and making disk-space reporting return the correct value, with regression coverage if the relevant test area is found.

Written by the indexing model from the issue text.