RFC: Add privacy and durability guidance for conversation links

[jonathansantilli]

conversation.url and related.url are useful but can be ephemeral, access-controlled, and sensitive.

Problem

Without guidance, implementations may assume links are durable/public or store artifacts containing secrets.

Proposal

Add a non-normative guidance section:

1. Treat links as potentially non-durable and authentication-dependent.
2. Treat linked prompts/tool outputs as potentially sensitive.
3. Recommend redaction and secret scanning before persistence/public sharing.
4. Recommend durable artifact links when long-term auditability is required.

Why This Should Be Added

1. Improves safety and operational realism.
2. Helps consumers interpret missing/expired links correctly.
3. Keeps schema unchanged while improving practical interoperability.

Compatibility

Documentation-only clarification; no schema break.

Scope

This is guidance for handling existing URL fields. It does not standardize authentication or access-control protocols.