Update CAP-78

[dmkozh]

There was some inconsistency around min_extension that I've clarified.

Also clarify the validation logic and justification for temporary entries.

[Copilot]

Pull request overview

This PR clarifies inconsistencies in the CAP-78 specification around min_extension and updates the TTL extension algorithm validation logic. The changes improve the clarity of how TTL extensions are computed and validated, particularly for temporary entries.

Changes:

• Clarified the TTL extension algorithm, simplifying the logic flow and adding explicit network limit computation
• Updated documentation to better explain the difference between min_extension and the old threshold parameter
• Added justification for validation behavior differences between network limits and user-provided arguments for temporary entries

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[anupsdf]

If in future TTL would be reimagined as time-based instead of number of ledgers, I wonder if we should do this CAP.

[dmkozh]

If in future TTL would be reimagined as time-based instead of number of ledgers, I wonder if we should do this CAP.

I don't think so. I'm not sure yet about the feasibility of time-based TTLs, and in general it seems like a topic that will take a while to figure out and agree on. This CAP is a quick win for the existing users, and if it works well, the time-based functions could resemble this interface (or we could even make the interface polymorphic).