C6: Runtime kernel owns data, status, error — adapters subscribe

The kernel is no longer a blind refetch pipe. Each context entry has:
  { data, status: idle|loading|success|error, error }

registerContext() returns { getState, subscribe, refetch, unregister }.
Adapters subscribe to state changes via callbacks. The kernel does
the fetch and notifies subscribers with the new state.

React adapter uses useSyncExternalStore for tear-free reads.
Vue adapter uses ref + subscribe callback.
Svelte adapter uses readable store backed by kernel subscription.

All three adapters also get:
- Mutation hooks with { mutate, isPending, error } (fixes H5)
- Vue: onServerPrefetch for Nuxt SSR (fixes M9)
- Svelte: readable store auto-cleans up on unsubscribe (fixes H9)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/mizan-django/generate/generator/lib/adapters/vue.mjs

@@ -1,5 +1,7 @@
 /**
  * Vue Stage 2 — Generates composables from Stage 1 output.
+ *
+ * Subscribes to the kernel for state. Vue reactivity wraps kernel notifications.
  */
 
 function pascalCase(str) {
@@ -15,12 +17,11 @@ export function generateVueAdapter(schema) {
     const lines = [
         '// AUTO-GENERATED by mizan — do not edit',
         '',
-        "import { ref, computed, watch, onMounted, onUnmounted, provide, inject, type Ref, type ComputedRef, type InjectionKey } from 'vue'",
-        "import { registerContext } from '@mizan/runtime'",
+        "import { ref, computed, onMounted, onUnmounted, onServerPrefetch, type ComputedRef } from 'vue'",
+        "import { registerContext, type ContextState } from '@mizan/runtime'",
         '',
     ]
 
-    // Stage 1 imports
     const stage1Imports = []
     for (const [ctxName] of Object.entries(contextGroups)) {
         const p = pascalCase(ctxName)
@@ -34,72 +35,70 @@ export function generateVueAdapter(schema) {
         lines.push('')
     }
 
-    // ── Context composables ─────────────────────────────────────────────
-
     for (const [ctxName, ctxMeta] of Object.entries(contextGroups)) {
         const p = pascalCase(ctxName)
         const ctxFunctions = functions.filter(fn => fn.isContext === ctxName)
         const paramEntries = Object.entries(ctxMeta.params || {})
+        const paramsArg = paramEntries.length > 0 ? 'params' : '{} as any'
 
-        lines.push(`// ${p} context`)
-        lines.push(`const ${p}Key: InjectionKey<{ data: Ref<${p}ContextData | null>, loading: Ref<boolean> }> = Symbol('${ctxName}')`)
-        lines.push('')
+        if (paramEntries.length > 0) {
+            lines.push(`export function use${p}Context(params: ${p}ContextParams) {`)
+        } else {
+            lines.push(`export function use${p}Context() {`)
+        }
 
-        // Provider composable
-        if (paramEntries.length > 0) {
-            lines.push(`export function provide${p}Context(params: { ${paramEntries.map(([k, v]) => `${k}: ${v.type === 'integer' || v.type === 'number' ? 'number' : 'string'}`).join(', ')} }) {`)
-        } else {
-            lines.push(`export function provide${p}Context() {`)
-        }
-        lines.push(`    const data = ref<${p}ContextData | null>(null)`)
-        lines.push(`    const loading = ref(true)`)
+        lines.push(`    const state = ref<ContextState<${p}ContextData>>({ data: null, status: 'idle', error: null })`)
+        lines.push(`    let handle: ReturnType<typeof registerContext> | null = null`)
         lines.push('')
-        lines.push(`    const refetch = async () => {`)
-        lines.push(`        loading.value = true`)
-        lines.push(`        try {`)
-        if (paramEntries.length > 0) {
-            lines.push(`            data.value = await fetch${p}Context(params as any)`)
-        } else {
-            lines.push(`            data.value = await fetch${p}Context({} as any)`)
-        }
-        lines.push(`        } catch (e) { console.error('[mizan] ${ctxName} fetch failed:', e) }`)
-        lines.push(`        loading.value = false`)
-        lines.push(`    }`)
-        lines.push('')
-        lines.push(`    let unregister: (() => void) | null = null`)
         lines.push(`    onMounted(() => {`)
-        lines.push(`        refetch()`)
-        if (paramEntries.length > 0) {
-            lines.push(`        unregister = registerContext('${ctxName}', params, refetch)`)
-        } else {
-            lines.push(`        unregister = registerContext('${ctxName}', {}, refetch)`)
-        }
+        lines.push(`        handle = registerContext('${ctxName}', ${paramsArg}, () => fetch${p}Context(${paramsArg}))`)
+        lines.push(`        handle.subscribe(() => { state.value = handle!.getState() })`)
+        lines.push(`        handle.refetch()`)
         lines.push(`    })`)
-        lines.push(`    onUnmounted(() => { unregister?.() })`)
         lines.push('')
-        lines.push(`    provide(${p}Key, { data, loading })`)
+        lines.push(`    onServerPrefetch(async () => {`)
+        lines.push(`        handle = registerContext('${ctxName}', ${paramsArg}, () => fetch${p}Context(${paramsArg}))`)
+        lines.push(`        await handle.refetch()`)
+        lines.push(`        state.value = handle.getState()`)
+        lines.push(`    })`)
+        lines.push('')
+        lines.push(`    onUnmounted(() => { handle?.unregister() })`)
+        lines.push('')
+        lines.push(`    return {`)
+        lines.push(`        state,`)
+        for (const fn of ctxFunctions) {
+            lines.push(`        ${fn.camelName}: computed(() => state.value.data?.${fn.name} ?? null) as ComputedRef<${fn.outputType} | null>,`)
+        }
+        lines.push(`        loading: computed(() => state.value.status === 'loading'),`)
+        lines.push(`        error: computed(() => state.value.error),`)
+        lines.push(`    }`)
         lines.push('}')
         lines.push('')
-
-        // Consumer composables
-        for (const fn of ctxFunctions) {
-            const hookPascal = pascalCase(fn.camelName)
-            lines.push(`export function use${hookPascal}(): ComputedRef<${fn.outputType} | null> {`)
-            lines.push(`    const ctx = inject(${p}Key)`)
-            lines.push(`    if (!ctx) throw new Error('use${hookPascal} requires provide${p}Context in a parent')`)
-            lines.push(`    return computed(() => ctx.data.value?.${fn.name} ?? null)`)
-            lines.push('}')
-            lines.push('')
-        }
     }
 
-    // ── Mutation composables ────────────────────────────────────────────
-
     for (const fn of [...mutations, ...plainFns]) {
         const p = pascalCase(fn.camelName)
-        lines.push(`export const use${p} = call${p}`)
+        lines.push(`export function use${p}() {`)
+        lines.push(`    const isPending = ref(false)`)
+        lines.push(`    const error = ref<Error | null>(null)`)
+        if (fn.hasInput) {
+            lines.push(`    async function mutate(args: Parameters<typeof call${p}>[0]) {`)
+        } else {
+            lines.push(`    async function mutate() {`)
+        }
+        lines.push(`        isPending.value = true; error.value = null`)
+        lines.push(`        try { return await call${p}(${fn.hasInput ? 'args' : ''}) }`)
+        lines.push(`        catch (e) { error.value = e as Error; throw e }`)
+        lines.push(`        finally { isPending.value = false }`)
+        lines.push(`    }`)
+        lines.push(`    return { mutate, isPending, error }`)
+        lines.push('}')
         lines.push('')
     }
 
+    lines.push("export type { ContextState } from '@mizan/runtime'")
+    lines.push("export { configure, initSession, MizanError } from '@mizan/runtime'")
+    lines.push('')
+
     return lines.join('\n')
 }