AFI conformance test suite

Substrate-level gate: same @client fixture registered in both backends
emits equivalent schemas, therefore the codegen produces equivalent
TypeScript regardless of which backend the frontend is generated against.
Catches adapter symmetry problems (Pydantic→OpenAPI converter divergence,
metadata leakage, ordering non-determinism) without docker, browser, or
Playwright.

What ships:

backends/mizan-fastapi/src/mizan_fastapi/schema.py — build_schema():
- Builds OpenAPI 3.0 from registered Mizan functions, mirroring the
  shape mizan-django's export emits.
- Drives FastAPI's native OpenAPI generation by registering a stub POST
  endpoint per function with its Input/Output Pydantic models, then
  appends x-mizan-functions and x-mizan-contexts extensions.
- Param-elevation logic mirrors mizan-django/src/mizan/export/__init__.py
  exactly (sharedBy tracking, required iff every function in context has
  the param).
- snake_to_camel and metadata field shapes match Django for byte-equality
  on the AFI surface.

tests/afi/ — the conformance harness:
- fixture.py: 5 @client functions covering the protocol axes (plain,
  context, mutation+affects). No channels/forms — those aren't AFI-common.
- django_app/: minimal Django project (settings, urls, AppConfig.ready
  registers the fixture). manage.py adds tests/afi/ to sys.path so both
  backends import the same fixture module.
- fastapi_app.py: thin make_app() that registers fixture and mounts router.
- schema_normalizer.py: drops backend-specific framing — Ninja-vs-FastAPI
  envelope differences (info/servers/tags), Django-only function fields
  (form metadata), x-mizan-channels. Plus afi_subset() and
  function_io_schemas() helpers for narrower comparisons.
- test_codegen_parity.py: three gates
  1. x-mizan-functions match across backends
  2. x-mizan-contexts match across backends
  3. Per-function Input/Output OpenAPI schemas match (what codegen feeds
     to openapi-typescript for type generation)

The full normalized OpenAPI envelopes do diverge — FastAPI adds
HTTPValidationError, the two converters wrap things slightly differently
in non-AFI-essential ways. That's not in the test scope. The codegen
only consumes x-mizan-functions, x-mizan-contexts, and the per-function
type schemas; those are what the test gates.

Makefile: test-afi target added; rolls into the test aggregate.

Verified: 3/3 conformance tests pass. Other surfaces unaffected —
mizan-core 15/15, mizan-django 348 pass, mizan-fastapi 11/11.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Makefile

@@ -1,9 +1,10 @@
-.PHONY: install test test-core test-django test-fastapi test-react test-integration docker-up docker-down clean
+.PHONY: install test test-core test-django test-fastapi test-react test-afi test-integration docker-up docker-down clean
 
 CORE = cores/mizan-python
 DJANGO = backends/mizan-django
 FASTAPI = backends/mizan-fastapi
 REACT = frontends/mizan-react
+AFI = tests/afi
 
 # ─── Setup ───────────────────────────────────────────────────────────────────
 
@@ -15,7 +16,7 @@ install:
 
 # ─── Unit Tests ──────────────────────────────────────────────────────────────
 
-test: test-core test-django test-fastapi test-react
+test: test-core test-django test-fastapi test-react test-afi
 
 test-core:
 	cd $(CORE) && uv run --extra dev pytest
@@ -29,6 +30,11 @@ test-fastapi:
 test-react:
 	cd $(REACT) && npm test
 
+# AFI conformance — verifies mizan-django and mizan-fastapi emit equivalent
+# schemas for the same @client fixture. Substrate-level gate, not e2e.
+test-afi:
+	cd $(AFI) && uv run pytest
+
 # ─── Integration Tests ──────────────────────────────────────────────────────
 
 test-integration: docker-up