Flatten to three packages + extract mizan-runtime

packages/
  mizan-runtime/   Framework-agnostic state engine (~150 lines)
                   Context registry, batched invalidation, fetch primitives
  mizan-django/    Django server adapter (was packages/mizan-rpc/adapters/django/)
                   Codegen moved to mizan-django/generate/
  mizan-react/     React adapter (was packages/mizan-csr/adapters/react/)

Removed premature abstractions: mizan-ast, mizan-schema, mizan-rpc,
mizan-csr, mizan-ssr stub packages. The actual architecture is three
concrete packages, not five abstract layers.

mizan-runtime implements the v1 spec: registerContext with params,
scoped invalidation via microtask batching, server-driven invalidation
from mutation responses, mizanFetch for context bundles, mizanCall for
mutations.

264 Django + 33 React tests pass.

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

packages/mizan-django/generate/generator/lib/fetch.mjs

@@ -0,0 +1,88 @@
+/**
+ * Schema Fetching
+ *
+ * Fetches mizan and channels schemas from Django management commands.
+ */
+
+import { spawn } from 'child_process'
+import path from 'path'
+
+/**
+ * Run a Django management command and parse JSON output.
+ */
+function runDjangoCommand(source, cwd, command) {
+  const managePath = path.resolve(cwd, source.django.managePath)
+  const manageDir = path.dirname(managePath)
+
+  let cmd, args
+  if (source.django.command) {
+    cmd = source.django.command[0]
+    args = [...source.django.command.slice(1), 'manage.py', command, '--indent', '0']
+  } else {
+    const python = source.django.python || 'python'
+    cmd = python
+    args = [managePath, command, '--indent', '0']
+  }
+
+  const env = source.django.env
+    ? { ...process.env, ...source.django.env }
+    : undefined
+
+  return new Promise((resolve, reject) => {
+    const proc = spawn(cmd, args, {
+      cwd: manageDir,
+      stdio: ['ignore', 'pipe', 'pipe'],
+      shell: process.platform === 'win32',
+      env,
+    })
+
+    let stdout = ''
+    let stderr = ''
+
+    proc.stdout.on('data', (data) => { stdout += data.toString() })
+    proc.stderr.on('data', (data) => { stderr += data.toString() })
+
+    proc.on('close', (code) => {
+      if (code !== 0) {
+        reject(new Error(`Django command failed (exit ${code}):\n${stderr}`))
+        return
+      }
+
+      const jsonStart = stdout.indexOf('{')
+      if (jsonStart === -1) {
+        reject(new Error(`No JSON found in Django output:\n${stdout}\n${stderr}`))
+        return
+      }
+
+      try {
+        resolve(JSON.parse(stdout.slice(jsonStart)))
+      } catch (err) {
+        reject(new Error(`Failed to parse JSON from Django:\n${err.message}\n${stdout}`))
+      }
+    })
+
+    proc.on('error', (err) => {
+      reject(new Error(`Failed to spawn Django command: ${err.message}`))
+    })
+  })
+}
+
+/**
+ * Fetch channels schema from Django.
+ */
+export async function fetchChannelsSchema(source, cwd) {
+  if (!source.django) {
+    throw new Error('Channels schema export requires django source configuration')
+  }
+  return runDjangoCommand(source, cwd, 'export_channels_schema')
+}
+
+/**
+ * Fetch mizan schema from Django.
+ */
+export async function fetchMizanSchema(source, cwd) {
+  if (!source.django) {
+    throw new Error('mizan schema export requires django source configuration')
+  }
+  return runDjangoCommand(source, cwd, 'export_mizan_schema')
+}