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>

tests/afi/schema_normalizer.py

@@ -0,0 +1,79 @@
+"""
+Normalize an OpenAPI schema dict so backend-specific framing doesn't make
+two semantically-equivalent schemas compare unequal.
+
+Drops:
+- Top-level OpenAPI envelope fields that vary trivially (info, servers, tags)
+- Django-only x-mizan-functions sub-fields (form metadata)
+- Django-only top-level extensions (x-mizan-channels)
+
+Sorts:
+- x-mizan-functions by name
+- components.schemas keys
+"""
+
+from __future__ import annotations
+
+from copy import deepcopy
+from typing import Any
+
+
+_DJANGO_ONLY_FUNCTION_FIELDS = {"isForm", "formName", "formRole", "formFields", "formFieldsError"}
+
+_OPENAPI_ENVELOPE_FIELDS_TO_DROP = {"info", "servers", "tags", "openapi"}
+
+
+def normalize(schema: dict[str, Any]) -> dict[str, Any]:
+    """Return a canonicalized copy suitable for deep-equal comparison."""
+    out = deepcopy(schema)
+
+    for k in _OPENAPI_ENVELOPE_FIELDS_TO_DROP:
+        out.pop(k, None)
+
+    out.pop("x-mizan-channels", None)
+
+    fns = out.get("x-mizan-functions") or []
+    for fn in fns:
+        for field in _DJANGO_ONLY_FUNCTION_FIELDS:
+            fn.pop(field, None)
+    out["x-mizan-functions"] = sorted(fns, key=lambda f: f["name"])
+
+    components = out.get("components", {})
+    schemas = components.get("schemas")
+    if isinstance(schemas, dict):
+        components["schemas"] = {k: schemas[k] for k in sorted(schemas)}
+
+    return out
+
+
+def afi_subset(schema: dict[str, Any]) -> dict[str, Any]:
+    """Just the AFI-essential surface — what every adapter must agree on."""
+    fns = schema.get("x-mizan-functions") or []
+    fns_clean = [
+        {k: v for k, v in fn.items() if k not in _DJANGO_ONLY_FUNCTION_FIELDS}
+        for fn in fns
+    ]
+    return {
+        "x-mizan-functions": sorted(fns_clean, key=lambda f: f["name"]),
+        "x-mizan-contexts": schema.get("x-mizan-contexts", {}),
+    }
+
+
+def function_io_schemas(schema: dict[str, Any]) -> dict[str, Any]:
+    """
+    Subset of components.schemas containing only the per-function Input/Output
+    models (what the codegen actually consumes for TypeScript type generation).
+    Drops backend-specific noise like HTTPValidationError, ValidationError,
+    that one backend emits and the other doesn't.
+    """
+    fns = schema.get("x-mizan-functions") or []
+    expected_names: set[str] = set()
+    for fn in fns:
+        if fn.get("inputType"):
+            expected_names.add(fn["inputType"])
+        if fn.get("outputType"):
+            expected_names.add(fn["outputType"])
+
+    components = schema.get("components", {})
+    schemas = components.get("schemas", {})
+    return {name: schemas[name] for name in sorted(expected_names) if name in schemas}