[dlinsley]

Description

Store.Meta() made two passes over storageIndex. The second pass re-loaded each source ID and asserted the result to *storage without checking whether the entry still existed. If the truncation loop deleted a source between the two passes, Load returned nil and the type assertion panicked.

The second pass existed only because meta.Count was never populated; it overwrote Count with tree.Size(). Maintain meta.Count on the storage whenever the tree changes (insertOrSwap and removeOldestEnvelope) and read it directly in Meta(). Meta() now makes a single pass and no longer re-loads from storageIndex.

Also resolved the goal of the TODO comment

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Testing performed?

• Unit tests
• Integration tests
• Acceptance tests

Checklist:

• This PR is being made against the main branch, or relevant version branch
• I have made corresponding changes to the documentation
• I have added testing for my changes

If you have any questions, or want to get attention for a PR or issue please reach out on the #logging-and-metrics channel in the cloudfoundry slack

[chombium]

LGTM!
Nice work @dlinsley and one nasty edge case bug is gone.