(v6) Post check takes up to hours and status unclear after passing

Any time the workflow reaches the post check for caching, it will hang on that step for minutes up to more than an hour before passing and the workflow reporting that it completed without issues.

The relevant portion from my workflow file:

name: Check for cache
  id: cache-build
  uses: actions/cache@v6
  with:
    path: |
          /usr
          /opt
          /agbcc
          /pokeemerald
          /bin
          key: default-cache

"Check for cache" step output:

Run actions/cache@v6
  with:
    path: /usr
  /opt
  /agbcc
  /pokeemerald
  /bin
  
    key: default-cache
    enableCrossOsArchive: false
    fail-on-cache-miss: false
    lookup-only: false
    save-always: false
Cache not found for input keys: default-cache

Post check step output:

Post job cleanup.
/usr/bin/tar --posix -cf cache.tzst --exclude cache.tzst -P -C /home/runner/work/modern-emerald-rebalanced/modern-emerald-rebalanced --files-from manifest.txt --use-compress-program zstdmt
/usr/bin/tar: ../../../../../opt/hca/diagnostics.json: Cannot open: Permission denied
/usr/bin/tar: Exiting with failure status due to previous errors
Warning: Failed to save: "/usr/bin/tar" failed with error: The process '/usr/bin/tar' failed with exit code 2

Also pretty default workflow environment:

Current runner version: '2.336.0'
Runner Image Provisioner
  Hosted Compute Agent
  Version: 20260729.566
  Commit: cf7153fe6e25b664e8693c24944bf2b00355d109
  Build Date: 2026-07-29T19:17:02Z
  Worker ID: {ef2689be-7dde-487b-8cff-00af7f79f784}
  Azure Region: eastus
Operating System
  Ubuntu
  24.04.4
  LTS
Runner Image
  Image: ubuntu-24.04
  Version: 20260816.277.1
  Included Software: https://github.com/actions/runner-images/blob/ubuntu24/20260816.277/images/ubuntu/Ubuntu2404-Readme.md
  Image Release: https://github.com/actions/runner-images/releases/tag/ubuntu24%2F20260816.277

Start by reproducing the post-job cache save with the workflow paths and Ubuntu runner details shown in the report. Inspect the cache action's post-job cleanup and tar error handling; done means the permission failure is handled or reported clearly without leaving the workflow apparently stalled for hours.