Severity for analysis-emitted diagnostics. The analyser populates
it for every diagnostic — lex-lsp reads diag.severity
directly when mapping onto the LSP wire. (Earlier the LSP layer
derived severity from DiagnosticKind; that mapping moved
upstream once the extension-emitted diagnostics needed
per-instance severities.)
Run the analyser without an extension registry — equivalent to
running with an empty registry. Provided for callers that haven’t
adopted the extension system yet.
Run the analyser with a populated extension registry. Labels whose
namespace is registered get pre-validated against their schema and,
if pre-validation passes, dispatched to the handler’s on_validate
hook. Handler-emitted diagnostics are merged into the same stream as
the built-in checks.