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-site/backend/testapp/clients.py

@@ -1,18 +1,9 @@
-"""
-Server functions and channels for integration tests.
-
-Registers everything the React integration test suite expects:
-- echo, add (HTTP + WebSocket RPC)
-- login, signup, add_email forms
-- chat, notifications, presence channels
-"""
-
 from django import forms
 from django.http import HttpRequest
 from pydantic import BaseModel
 
 from mizan.client import ServerFunction, client
-from mizan.channels import ReactChannel
+from mizan.channels import Channel
 from mizan.setup import register, register_form, register_as
 from mizan.channels import register as register_channel
 from mizan.forms import mizanFormMixin, mizanFormMeta
@@ -85,7 +76,7 @@ class LoginForm(forms.Form):
 
 
 def handle_login(request, form):
-    """Login form submit handler."""
+    """Authenticate the credentials and open a session."""
     from django.contrib.auth import authenticate, login
 
     user = authenticate(
@@ -109,7 +100,7 @@ class SignupForm(forms.Form):
 
 
 def handle_signup(request, form):
-    """Signup form submit handler."""
+    """Create the user, surfacing any creation failure as a form error."""
     from django.contrib.auth import get_user_model
 
     User = get_user_model()
@@ -118,11 +109,12 @@ def handle_signup(request, form):
             email=form.cleaned_data["email"],
             password=form.cleaned_data["password1"],
         )
-        return {"success": True, "data": {"user_id": user.pk}}
     except Exception as e:
         form.add_error(None, str(e))
         return None
 
+    return {"success": True, "data": {"user_id": user.pk}}
+
 
 register_form(SignupForm, "signup", submit_handler=handle_signup)
 
@@ -139,36 +131,35 @@ register_form(AddEmailForm, "add_email")
 # =============================================================================
 
 
-class ChatChannel(ReactChannel):
+class ChatChannel(Channel):
     class Params(BaseModel):
         room: str
 
-    class ReactMessage(BaseModel):
+    class ClientMessage(BaseModel):
         text: str
 
-    class DjangoMessage(BaseModel):
+    class ServerMessage(BaseModel):
         text: str
 
     def authorize(self, params=None):
-        return True
+        return bool(params and params.room)
 
     def group(self, params=None):
-        room = params.room if params else "default"
-        return f"chat_{room}"
+        return f"chat_{params.room}"
 
     def receive(self, params, msg):
-        return self.DjangoMessage(text=msg.text)
+        return self.ServerMessage(text=msg.text)
 
 
 register_channel(ChatChannel, "chat")
 
 
-class NotificationsChannel(ReactChannel):
-    class DjangoMessage(BaseModel):
+class NotificationsChannel(Channel):
+    class ServerMessage(BaseModel):
         text: str
 
     def authorize(self, params=None):
-        return True
+        return self.user.is_authenticated
 
     def group(self, params=None):
         return "notifications_global"
@@ -177,12 +168,12 @@ class NotificationsChannel(ReactChannel):
 register_channel(NotificationsChannel, "notifications")
 
 
-class PresenceChannel(ReactChannel):
-    class DjangoMessage(BaseModel):
+class PresenceChannel(Channel):
+    class ServerMessage(BaseModel):
         value: int
 
     def authorize(self, params=None):
-        return True
+        return self.user.is_authenticated
 
     def group(self, params=None):
         return "presence_global"
@@ -290,24 +281,34 @@ class Multiply(ServerFunction):
 
 
 # =============================================================================
-# Error-producing Functions
+# Functions carrying error branches
 # =============================================================================
 
 
-@client
-def not_implemented_fn(request: HttpRequest) -> EchoOutput:
-    raise NotImplementedError("This feature is not yet implemented")
-
-
-register(not_implemented_fn, "not_implemented_fn")
+_ECHO_TRANSFORMS = {"upper": str.upper, "lower": str.lower}
 
 
 @client
-def buggy_fn(request: HttpRequest) -> EchoOutput:
-    raise RuntimeError("Unexpected internal failure")
+def echo_transform(request: HttpRequest, text: str, mode: str) -> EchoOutput:
+    transform = _ECHO_TRANSFORMS.get(mode)
+    if transform is None:
+        raise NotImplementedError(f"echo mode {mode!r} has no transform")
+    return EchoOutput(message=transform(text))
 
 
-register(buggy_fn, "buggy_fn")
+register(echo_transform, "echo_transform")
+
+
+class DivideOutput(BaseModel):
+    quotient: float
+
+
+@client
+def divide(request: HttpRequest, numerator: int, denominator: int) -> DivideOutput:
+    return DivideOutput(quotient=numerator / denominator)
+
+
+register(divide, "divide")
 
 
 @client
@@ -384,16 +385,16 @@ class ItemForm(mizanFormMixin, forms.Form):
 
 
 # =============================================================================
-# Auth-gated Channel
+# Staff-gated Channel
 # =============================================================================
 
 
-class PrivateChannel(ReactChannel):
-    class DjangoMessage(BaseModel):
+class PrivateChannel(Channel):
+    class ServerMessage(BaseModel):
         text: str
 
     def authorize(self, params=None):
-        return getattr(self.user, "is_authenticated", False)
+        return self.user.is_staff
 
     def group(self, params=None):
         return "private_global"

examples/django-react-site/backend/testapp/settings.py

@@ -1,14 +1,11 @@
-"""
-Django settings for the integration test backend.
-
-Provides:
-- HTTP server functions (echo, add)
-- WebSocket channels (chat, notifications, presence)
-- JWT authentication
-- Form integration (login, signup, add_email)
-"""
+"""Django settings for the integration-test backend the E2E harness talks to."""
 
 import os
+from pathlib import Path
+
+# The directory holding manage.py and the app packages; mizan's client
+# discovery walks the installed apps beneath it.
+BASE_DIR = Path(__file__).resolve().parent.parent
 
 SECRET_KEY = "integration-test-secret-key-not-for-production"
 
@@ -41,7 +38,7 @@ TEMPLATES = [
         "OPTIONS": {
             "worker": os.path.join(
                 os.path.dirname(__file__), "..", "..", "..", "..",
-                "packages", "mizan-ssr", "src", "worker.tsx",
+                "workers", "mizan-ssr", "src", "worker.tsx",
             ),
         },
     },