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>

backends/mizan-ts/src/decorator.ts

@@ -1,18 +1,3 @@
-/**
- * Mizan @client decorator and function wrapper.
- *
- * Two registration styles:
- *
- * 1. Function wrapper (standalone functions):
- *    const userProfile = client({ context: UserCtx }, async (userId: number) => { ... })
- *
- * 2. Class decorator (methods):
- *    class Handlers {
- *      @client({ context: UserCtx })
- *      async userProfile(userId: number) { ... }
- *    }
- */
-
 import { ReactContext, type ClientOptions, type RegistryEntry, type ParamDef } from './types'
 import { register } from './registry'
 
@@ -35,8 +20,14 @@ function normalizeAffects(
     })
 }
 
+/**
+ * Recover parameter names by parsing the function's own source text.
+ *
+ * Names are the wire contract — the dispatcher matches request params to
+ * positional arguments by name — and JS erases them at runtime, so the
+ * source string is the only place they survive.
+ */
 function extractParams(fn: Function): ParamDef[] {
-    // Extract parameter names from function.toString()
     const source = fn.toString()
     const match = source.match(/\(([^)]*)\)/)
     if (!match || !match[1].trim()) return []
@@ -46,33 +37,22 @@ function extractParams(fn: Function): ParamDef[] {
         .map(p => p.trim())
         .filter(p => p && !p.startsWith('...'))
         .map(p => {
-            // Handle destructured defaults: name = default, name: type
+            // Strips a default value or a type annotation off the name
             const name = p.split(/[=:]/)[0].trim()
             return { name, type: 'any', required: !p.includes('=') }
         })
 }
 
-/**
- * Function wrapper — registers a standalone function.
- *
- * const userProfile = client({ context: UserCtx }, async (userId: number) => { ... })
- */
+/** Wrap and register a standalone function. */
 export function client<T extends (...args: any[]) => Promise<any>>(
     options: ClientOptions,
     fn: T,
 ): T
 
-/**
- * Class method decorator.
- *
- * class Handlers {
- *   @client({ context: UserCtx })
- *   async userProfile(userId: number) { ... }
- * }
- */
+/** Register a class method. */
 export function client(options: ClientOptions): MethodDecorator
 
-export function client(optionsOrFn: ClientOptions | ClientOptions, fn?: Function): any {
+export function client(optionsOrFn: ClientOptions, fn?: Function): any {
     // Function wrapper form: client(options, fn)
     if (fn && typeof fn === 'function') {
         const options = optionsOrFn as ClientOptions
@@ -85,16 +65,17 @@ export function client(optionsOrFn: ClientOptions | ClientOptions, fn?: Function
 
         const name = fn.name || 'anonymous'
         const params = extractParams(fn)
-        const isView = false // Determined at call time for function wrappers
 
         const entry: RegistryEntry = {
             name,
-            fn: fn as any,
+            fn: fn as RegistryEntry['fn'],
             context,
             affects,
             params,
             private: options.private ?? false,
-            viewPath: isView,
+            // A wrapped function's return is only known once called, so the
+            // view-vs-RPC split is decided by the dispatcher, not here.
+            viewPath: false,
             route: options.route,
             methods: options.methods,
             auth: options.auth,