docs(planning): record decision to keep ClassProperty media_type#20
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Architecture-review candidate 3 proposed collapsing the ClassProperty descriptor + per-route VersionedJSONResponse. Rejected: the descriptor's lazy class-level read is what decouples init_fastapi_versioning timing from route registration. The README calls init after include_router; the tests call it before; both work only because of that laziness. Every collapse (eager init resolution, startup hook, or middleware content-type) trades it for an init-ordering contract, lifespan coupling, or over-stamping non-versioned responses. Records the constraint and revisit triggers. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Records the outcome of architecture-review candidate 3 (collapse the
ClassPropertydescriptor + per-routeVersionedJSONResponse).Decision: rejected. The descriptor stays.
Why
The deciding discovery:
ClassProperty's lazy class-level read is what makesinit_fastapi_versioningorder-independent with respect toinclude_router. The two shipped usages prove it by disagreeing:README.md—include_router(...)theninit_fastapi_versioning(...)(init last).tests/conftest.py—init_fastapi_versioning(...)theninclude_router(...)(init first).Both work only because the vendor is read lazily at access time. Every proposed collapse trades that away:
initby iteratingapp.routes) requires routes to be mounted first → imposes an "init last" contract and breaks the init-first order.initinto app lifespan.VersionedAPIRouteresponse from a plain one at ASGI send time, so it would over-stamp the vendor content-type onto non-versioned responses.Mechanics verified against FastAPI 0.139.0 / Starlette 1.3.1 (
openapi/utils.py:279readsresponse_class.media_typelive at schema-gen;APIRoute.__init__captures the class object in the handler closure). Full rationale and revisit triggers in the decision file.No code changes.
just check-planning→planning: OK; appears under## Decisionsinjust index.