Function unsupported_identifier_claim 

pub fn unsupported_identifier_claim(kind: &str, value: &str) -> String

The claim ParseError::UnsupportedIdentifier makes, without the entry {entry_key:?} prefix its Display carries.

Callers that put entry_key in a field of its own – the CLI verify row and the MCP batch_from_bibliography envelope both do – would otherwise say it twice. One definition rather than a copy at each site, because the copies drifted: two of the three carried a run of joined-line whitespace into user-facing output before anything asserted the text.