External schema-file $ref without a #/components/... fragment is not resolved into a model

[joseegman-idoneea]

External schema-file $ref without a #/components/... fragment is not resolved into a model

Summary

When a schema is referenced as a whole external file — i.e. the file is the schema and
the $ref carries no JSON-pointer fragment — the generator does not turn it into a model.
The operation is generated referencing a DTO that is never emitted, so the generated code
does not compile.

This is the modular-contract style produced by tools like redocly split:

# response content
schema:
  $ref: "./components/schemas/Dashboard.yml"   # whole file is the schema, no #/... fragment

# components/schemas/Dashboard.yml  (the file IS the schema object)
type: object
properties:
  id: { type: string }

Related

Split off from #372 (external Path Item $ref, now fixed). While validating that fix,
a modular contract that also split its schemas into standalone files surfaced this
independent gap. The path-item fix makes the API interface generate; this gap keeps the
corresponding model from generating.

How to reproduce

Reference a schema by whole external file (no fragment) from a response/request/component,
then generate. The API interface is produced and imports e.g.
InlineResponse200GetDashboardDTO / DashboardDTO, but no such model class is written.

Expected

The external file is loaded and generated as a model, named after the referenced file /
component, identical to referencing an inlined equivalent.

Actual

Operation generated referencing a non-existent DTO; no model file emitted; no warning.
Generated sources fail to compile.

Notes / current workaround

The supported external form is a fragment ref into a components-style file, e.g.
$ref: "components.yml#/components/schemas/Dashboard" (see the existing
testExternalRefsGeneration fixture). Contracts using whole-file schema refs must currently
either be bundled/inlined or rewritten to the fragment form.

Root cause pointers

• ApiTool.getComponentSchemas (common/tools/ApiTool.java:157-171) stores
  components.schemas.X nodes raw; an external-file $ref entry is not dereferenced.
• Response/request schema handling (openapi/utils/OpenApiUtil.processResponses /
  MapperPathUtil schema-type resolution) only registers inline object schemas or
  fragment component refs as models; a whole-file external $ref matches neither and is
  named as an inline response but never emitted.

Proposed fix

Mirror the Path Item resolution added in #372: dereference whole-file schema $refs (external,
no fragment) at parse time — for components.schemas entries and for request/response content
schemas — substituting the loaded schema node so the existing model pipeline emits it. Add a
regression fixture with schemas split into standalone files.