[SandObserver]

Summary

• Store keepMs on each latest() entry and prune every entry by its own value, not the caller's.
• A health poll with a 2-minute keep no longer drops widget-data results kept for 15 minutes.

Testing
All green. Added a test that a short-keep key does not drop a long-keep one.

Changelog

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.