Each coverage run leaves ~50 six-byte /tmp/CodeCoverage.* files behind on Linux (18.11.x) #252

TL;DR: On Linux, each dotnet test --coverage run leaves about 50 six-byte /tmp/CodeCoverage.* files behind in my runs. Versions 18.11.0 and 18.11.2 do this; 18.10.0 left none under the same test configurations. The files are never removed, so they accumulate when tests run repeatedly.

Package: Microsoft.Testing.Extensions.CodeCoverage 18.11.0 and 18.11.2 (the latest at the time of writing)
Runtime: .NET 8 and .NET 10 hosts, Linux x64, xunit.v3 3.2.2 on Microsoft.Testing.Platform
Context: split out of #232. Version 18.11.2 fixed the issue reported there. The measurements are in this comment.

Summary

Each dotnet test --coverage run leaves small files in /tmp that are never removed: 52 on net8.0 and 54 on net10.0 in my runs. They are named /tmp/CodeCoverage.<session>.<guid>, have mode 0600, and are six bytes long, all containing 02 00 00 00 00 00.

TryDeleteBackingFile does remove the real coverage buffer (the 1,633-byte one in this test), so only these small files leak. For comparison, 18.10.0 left none behind under the same test configurations. On a CI runner or developer machine that runs tests repeatedly, they accumulate without bound.