Why

Every element struct in openapi3 (Info, License, Paths, Operation, ...) carries an Origin so consumers can attach file/line/column to it. T itself does not. As a result the document-root fields (openapi, info, paths, webhooks, jsonSchemaDialect) have no source location, even when the document is loaded with Loader.IncludeOrigin = true. A consumer reporting "openapi is required" can name the file but not the line.

What

Add Origin *Origin to T. No loader change is needed: yaml3 already injects an __origin__ entry into the document's root mapping, oasdiff/yaml already surfaces it as the root OriginTree.Origin, and applyOriginsToStruct already sets the Origin field on any struct that has one tagged json:"-". T simply never had the field.

Wire it into the doc-root validation errors. The six constructors for doc-root findings previously passed nil for origin (their comments said the loader "doesn't track" *T, now obsolete):

• newOpenAPIVersionRequired
• newInfoRequired
• newPathsRequired
• newJSONSchemaDialectAbsoluteURIRequired
• newWebhooksFieldFor31Plus
• newJSONSchemaDialectFieldFor31Plus

Each now takes an origin *Origin, and T.Validate passes doc.Origin. The resulting RequiredFieldError / FieldVersionMismatchError carries it like every other typed error.

Resolution granularity matches kin's existing Origin model:

• Scalar root fields (openapi, jsonSchemaDialect) resolve precisely via Origin.Fields[name].
• Object / missing root fields (info, paths, webhooks) fall back to Origin.Key (the document root) — still a file and position, just not the exact key.

Compatibility

Error() strings are unchanged. The new field is json:"-" yaml:"-", so marshalling is unaffected, and Origin is only populated when IncludeOrigin is set (opt-in, as before).

Tests

• TestOrigin_T — doc.Origin is populated; Origin.Fields["openapi"] resolves to the openapi: line.
• TestValidationError_OriginForDocumentRootFields — replaces TestValidationError_OriginNilForDocumentRootFields, which pinned the old "doc-root fields have nil Origin" behavior; now asserts the doc-root error carries T.Origin.

Full suite green; .github/docs/openapi3.txt regenerated.