Zero Slop v2.12.26

Release 2.12.26: expose safe editor diagnostics

• Retain allowlisted provider failure metadata in gateway diagnostics

• Expose bounded editor diagnostics in gateway results

• Release 2.12.26 with safe gateway diagnostics

• Refresh optional diagnostic contract fixtures for release

• Generate opaque provider-error test data

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Co-authored-by: Codex codex@local