[REQ][Kotlin] Fake mock library on OpenAPI examples

Many Kotlin/mobile developers need to work with APIs without depending on a running backend. Currently, offline development or mock flavors require either:

• Maintaining large amounts of hand-written or recorded JSON mock data
• Writing custom fake clients by hand

This is time-consuming, error-prone, and difficult to maintain when the API changes.

Describe the solution you'd like

I propose adding a new Kotlin client library type:

--library=fake

This would generate:

1. Standard models (unchanged)
2. Standard API interfaces (unchanged)
3. Fake API implementations (FakeApi) for each API interface

Each fake API method would return data derived from the OpenAPI specification:

• Example fields, if present
• Default values, if present
• Schema-derived fake data as fallback (strings, numbers, enums, nested objects, arrays)

This approach produces a fully on-device mock client, with no server, Docker, or Node process required.

Describe alternatives you've considered

• WireMock / MockWebServer / Prism / Mockoon

  • Requires running an embedded server or Node process
  • Not practical for Android mock flavors
  • Harder to keep in sync with API changes

• Manually creating fake clients per API

  • High maintenance burden
  • Error-prone and repetitive
  • Difficult to scale for large APIs

Additional context

Start by tracing Kotlin client generation and the existing --library options, then compare how API interfaces and models are produced. Define the fake library's behavior for examples, defaults, and schema-derived values, and verify that each API gets a usable FakeApi implementation without a server or external process.