Refuse repaired Unicode in release source observations #497

🤖 Generated by the Agentic Engineer

Problem

The release JSON boundary accepts malformed UTF-8 and unpaired surrogate escapes. Candidate preparation can consequently rewrite a committed description while reporting successful preparation.

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

• Refuse malformed original Unicode before parsing any release manifest or retained native observation.
• Preserve valid international text, paired surrogates and literal replacement characters.
• Prove failure before candidate output is created and preserve otherwise-valid preparation controls.

Size: S/M. Part of #101.