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/app.py

@@ -1,10 +1,5 @@
 #!/usr/bin/env python
-"""
-mizan Desktop — PyWebView + Django local RPC.
-
-Starts a local Django ASGI server and opens a native desktop window.
-All communication between the UI and backend uses mizan server functions.
-"""
+"""Launcher: runs the Django ASGI server locally and opens it in a native window."""
 
 import os
 import sys
@@ -13,19 +8,18 @@ import time
 
 os.environ.setdefault("DJANGO_SETTINGS_MODULE", "backend.settings")
 
-# Work around Qt WebEngine GPU crashes on some systems
+# Qt WebEngine crashes on some GPU/driver combinations unless it renders on CPU.
 os.environ.setdefault("QTWEBENGINE_CHROMIUM_FLAGS", "--disable-gpu")
 
 
 def start_server(host: str, port: int):
-    """Start the Django ASGI server in a background thread."""
     import django
 
     django.setup()
 
-    # Run migrations on first launch
     from django.core.management import call_command
 
+    # --run-syncdb builds the tables on a first launch with no migration files.
     call_command("migrate", "--run-syncdb", verbosity=0)
 
     import uvicorn
@@ -38,51 +32,49 @@ def start_server(host: str, port: int):
     )
 
 
-def wait_for_server(url: str, timeout: float = 10.0):
-    """Poll until the server responds."""
+def wait_for_server(url: str, timeout: float = 10.0) -> None:
+    """Poll until the server answers, or raise carrying the last refusal."""
     from urllib.request import urlopen
-    from urllib.error import URLError
 
     deadline = time.time() + timeout
+    last_error: OSError | None = None
     while time.time() < deadline:
         try:
             urlopen(url, timeout=1)
-            return True
-        except (URLError, OSError):
+            return
+        except OSError as e:
+            last_error = e
             time.sleep(0.1)
-    return False
+
+    raise TimeoutError(
+        f"Django server did not answer {url} within {timeout}s"
+    ) from last_error
 
 
 def main():
     host = "127.0.0.1"
     port = 8765
 
-    # Start Django in a daemon thread
     server = threading.Thread(target=start_server, args=(host, port), daemon=True)
     server.start()
 
     base_url = f"http://{host}:{port}"
-
-    if not wait_for_server(f"{base_url}/api/mizan/session/"):
-        print("ERROR: Django server failed to start", file=sys.stderr)
-        sys.exit(1)
+    wait_for_server(f"{base_url}/api/mizan/session/")
 
     print(f"Backend running at {base_url}")
 
-    # Check if --headless flag is passed (for testing)
     if "--headless" in sys.argv:
         print("Headless mode — server running. Press Ctrl+C to stop.")
         try:
             while True:
                 time.sleep(1)
         except KeyboardInterrupt:
-            pass
+            print("Interrupted — stopping the server.", file=sys.stderr)
         return
 
-    # Open native window
     import webview
 
-    window = webview.create_window(
+    webview.create_window(
         title="mizan Desktop",
         url=base_url,
         width=1024,