Function validate_with_policy 

pub fn validate_with_policy(
    doc: &Document,
    policy: &DiagnosticPolicy,
    brand: &BrandContract,
) -> ValidationReport

Run the full document validation pass, applying an externally supplied policy and brand contract at their respective choke points.

The caller is responsible for assembling policy (e.g. merging config-file and CLI-flag policy with the document’s in-file policy) and brand (e.g. merging global/local config brand contracts with the document’s in-file brand { … } block). Passing &doc.diagnostic_policy and &doc.brand_contract reproduces validate exactly.

Internally runs resolve_tokens on doc.tokens, merges those diagnostics, then walks the full document collecting all semantic diagnostics. Never hard-fails; all findings are returned in the ValidationReport.