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-react/src/errors.ts

@@ -0,0 +1,107 @@
+/**
+ * Django Server Error Types
+ *
+ * Typed errors for server function failures.
+ */
+
+/**
+ * Error codes returned by the server
+ */
+export type ErrorCode =
+    | 'NOT_FOUND'
+    | 'VALIDATION_ERROR'
+    | 'UNAUTHORIZED'
+    | 'FORBIDDEN'
+    | 'BAD_REQUEST'
+    | 'INTERNAL_ERROR'
+    | 'NOT_IMPLEMENTED'
+
+/**
+ * Error response structure from the server
+ */
+export interface FunctionErrorResponse {
+    error: true
+    code: ErrorCode
+    message: string
+    details?: {
+        fields?: Record<string, string[]>
+        required?: string[]
+        type?: string
+        [key: string]: unknown
+    }
+}
+
+/**
+ * Error thrown when a server function call fails
+ */
+export class DjangoError extends Error {
+    /**
+     * Error code from the server
+     */
+    readonly code: ErrorCode
+
+    /**
+     * Additional error details
+     */
+    readonly details?: FunctionErrorResponse['details']
+
+    /**
+     * The original error response
+     */
+    readonly response: FunctionErrorResponse
+
+    constructor(response: FunctionErrorResponse) {
+        super(response.message)
+        this.name = 'DjangoError'
+        this.code = response.code
+        this.details = response.details
+        this.response = response
+
+        // Maintains proper stack trace for where error was thrown
+        if (Error.captureStackTrace) {
+            Error.captureStackTrace(this, DjangoError)
+        }
+    }
+
+    /**
+     * Check if this is a validation error
+     */
+    isValidationError(): boolean {
+        return this.code === 'VALIDATION_ERROR'
+    }
+
+    /**
+     * Check if this is an authentication error
+     */
+    isAuthError(): boolean {
+        return this.code === 'UNAUTHORIZED' || this.code === 'FORBIDDEN'
+    }
+
+    /**
+     * Check if this is a not found error
+     */
+    isNotFound(): boolean {
+        return this.code === 'NOT_FOUND'
+    }
+
+    /**
+     * Get field-level validation errors (if this is a validation error)
+     */
+    getFieldErrors(): Record<string, string[]> | null {
+        if (this.code === 'VALIDATION_ERROR' && this.details?.fields) {
+            return this.details.fields
+        }
+        return null
+    }
+
+    /**
+     * Get error for a specific field
+     */
+    getFieldError(field: string): string | null {
+        const errors = this.getFieldErrors()
+        if (errors && errors[field]?.length > 0) {
+            return errors[field][0]
+        }
+        return null
+    }
+}