A channel's message slots are named from the client, on every backend

The IR called them react-message and django-message, so a FastAPI channel had
to declare a DjangoMessage. They are client-message and server-message now,
and the direction words hold wherever a channel is declared: Params /
ClientMessage / ServerMessage, with mizan-core deriving <Pascal>Params and
friends so no backend names a type itself. Django's ReactChannel and
FastAPI's ReactChannel are both Channel.

mizan-fastapi never registered a channels extension, so build_ir() emitted no
channel at all and every payload type was invisible to codegen. It registers
one now. RegistryExtension is an ABC requiring all(), which is what the IR
reads — an extension that cannot enumerate its registrations no longer exists.

The gate that should have caught the rename could not: tests/afi registered no
channel because mizan-rust had no channel registry to register one in, so a
five-package rename of the wire contract passed byte-parity without a channel
byte crossing it. mizan-rust grows ChannelSlotKind, a CHANNELS slice, a
#[mizan::channel] macro, and KDL emission whose wire_to_pascal matches Python's
split; the AFI fixture now carries a channel with every slot and one with a
single slot, so all three backends prove the contract byte for byte.

MizanChannel held three Option<String> beside three has_*() predicates and
unwrapped them with defaults; it holds an ordered slot vector, so an absent
slot is absent rather than defaulted. The channels target emitted a React
hooks file that a stage1-only consumer could not compile — react emits that
now. The codegen's parity tests byte-compared emitted source against baselines
without ever compiling it: they compile the generated crate and run its tests,
import the generated Python package and call every method, and typecheck each
TypeScript target against a consumer.

Also fixed at source: app_visitor printed its import diagnostic to stdout, the
stream export_mizan_ir writes KDL to, so a failed import silently corrupted the
IR; the apps root was hardcoded to "apps"; _default_literal crashed build_ir on
any non-JSON-serializable field default; Django and mizan-core derived Pascal
names two different ways, disagreeing on every dotted channel name.

ir.py builds a document and renders templates/ir/document.kdl.j2 rather than
appending KDL strings with hand-tracked indentation, and named types resolve to
a fixed point — a model reachable only through a union branch was referenced by
a ref that no type block ever defined.

The rest is the write-gate's own classifiers run over the standing tree:
relative imports, silent swallows, Protocol contracts that should be ABCs,
emitters hand-rendering target source, catch-all arms over closed enums, and
comments narrating the project rather than the code.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

examples/django-react-desktop-app/tests/live_http.py

@@ -0,0 +1,81 @@
+import json
+from dataclasses import dataclass
+from typing import Any
+from urllib.request import HTTPErrorProcessor, Request, build_opener, urlopen
+
+
+class _KeepErrorResponses(HTTPErrorProcessor):
+    # urllib's default processor converts every non-2xx into a raised
+    # HTTPError. The RPC endpoint carries its error envelope in the body of a
+    # 4xx/5xx, so the response object has to reach the caller intact.
+    def http_response(self, request, response):
+        return response
+
+    https_response = http_response
+
+
+_opener = build_opener(_KeepErrorResponses)
+
+
+@dataclass(frozen=True)
+class Reply:
+    status: int
+    raw: bytes
+
+    @property
+    def body(self) -> dict[str, Any]:
+        # Django's own CSRF and 500 pages are HTML, so decoding is deferred to
+        # the tests that actually assert on the mizan envelope.
+        return json.loads(self.raw)
+
+
+def _send(req: Request) -> Reply:
+    resp = _opener.open(req)
+    return Reply(status=resp.status, raw=resp.read())
+
+
+class LiveRPCMixin:
+    """HTTP access to the mizan endpoints on a LiveServerTestCase server."""
+
+    csrf_token: str = ""
+    cookies: str = ""
+
+    def session_init(self) -> None:
+        url = f"{self.live_server_url}/api/mizan/session/"
+        resp = urlopen(Request(url))
+        for cookie in resp.headers.get_all("Set-Cookie") or []:
+            if "csrftoken=" in cookie:
+                self.csrf_token = cookie.split("csrftoken=")[1].split(";")[0]
+                self.cookies = f"csrftoken={self.csrf_token}"
+                return
+        self.csrf_token = ""
+        self.cookies = ""
+
+    def get(self, path: str) -> Reply:
+        return _send(Request(f"{self.live_server_url}{path}"))
+
+    def post(
+        self,
+        path: str,
+        body: bytes | str,
+        content_type: str = "application/json",
+        with_csrf: bool = True,
+    ) -> Reply:
+        if isinstance(body, str):
+            body = body.encode()
+        req = Request(f"{self.live_server_url}{path}", data=body, method="POST")
+        req.add_header("Content-Type", content_type)
+        if with_csrf and self.csrf_token:
+            req.add_header("X-CSRFToken", self.csrf_token)
+            req.add_header("Cookie", self.cookies)
+        return _send(req)
+
+    def call(self, fn: str, args: dict | None = None, with_csrf: bool = True) -> Reply:
+        payload = json.dumps({"fn": fn, "args": args or {}})
+        return self.post("/api/mizan/call/", payload, with_csrf=with_csrf)
+
+    def result(self, fn: str, args: dict | None = None) -> Any:
+        """The `result` payload of a call that must have succeeded."""
+        reply = self.call(fn, args)
+        self.assertEqual(reply.status, 200, reply.raw)
+        return reply.body["result"]