The engineer registered verdict meta and the meta box against 'pr_peptide'
which does not exist. PR Core registers the CPT as 'peptide'. Result: the
verdict meta box was invisible in wp-admin and meta was not exposed in REST.
All functional register_post_meta and add_meta_box calls now target 'peptide'.
No data migration needed — post meta is keyed by meta_key, not CPT.
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