backup validate fails on demo-created backups

[maximilien]

Bug

weave backup validate fails on backups created during demo runs (e.g., opik demo, ai-alliance demo).

Steps to reproduce

weave backup create OpikDemo --output /tmp/opik-demo.weavebak --weaviate-cloud
weave backup validate /tmp/opik-demo.weavebak

Expected

Validation passes.

Actual

Validation fails (exact error TBD — observed during live demo recording).

Context

Affects all demo scripts that include the backup/restore section.

[maximilien]

Marking as bug (p1). This appears to be a regression on demo-created backups. Will be addressed alongside #65 (Backup & Restore). If you have a failing backup ID example, please share for faster repro.