Require complete tag-pagination metadata before proposing releases #500

🤖 Generated by the Agentic Engineer

Problem

The proposal evaluator accepts a terminal tag page with a missing or wrongly typed end cursor and returns PREPARED, treating an incomplete observation as proposal clearance.

Proposed direction

Repair the owning observation or output boundary, with a regression that fails on current main before changing the implementation. Preserve the existing conservative behavior and public interface.

Acceptance criteria

• Require both page-info keys, a boolean continuation flag and a valid cursor representation on every page.
• Preserve legitimate terminal cursors for populated connections and explicit null for empty terminal connections.
• Exercise missing/type-invalid keys through the actual offline proposal command and retain UNKNOWN with no write authority.

Size: S/M. Part of #101.