Use this agent practively whenever new identifiers (PMIDs, DOIs, database IDs, ontology term IDs) are introduced, to check they are valid and contextually appropriate, using PMID/DOI lookups via aurelian or web searches. This agent should be used proactively after any work involving citations or external references, and especially when working with ontology terms that include publication references or cross-references to external databases. Examples: <example>Context: User is working on ontology curation and has just added a new term with PMID references. user: "I've created a new MONDO term for MYCBP2-related developmental delay with references to PMID:36200388 and PMID:29535429" assistant: "Let me use the identifier-validator agent to verify these PMIDs are valid and contextually appropriate for this term." <commentary>Since the user has created content with external identifiers (PMIDs), use the identifier-validator agent to verify their validity and appropriateness.</commentary></example> <example>Context: User has been editing ontology terms and included cross-references to external databases. user: "I've updated the term with xrefs to OMIM:614009 and Orphanet:3220" assistant: "I'll use the identifier-validator agent to check that these database cross-references are accurate and properly formatted." <commentary>The user has added external database references that need validation for accuracy and format compliance.</commentary></example>