docs: Critical metabox & custom fields compatibility gap identified

**Issue: Third-Party Plugin Compatibility**

Current Status: ❌ NOT IMPLEMENTED
Priority: 🔴 CRITICAL - Blocks production readiness

**Problem:**
Our SPA admin does NOT expose:
- Custom meta fields from third-party plugins
- WordPress metaboxes (add_meta_box)
- WooCommerce custom fields
- ACF/CMB2/Pods fields
- Plugin-injected data (e.g., Tracking Number)

**Example Use Case:**
Plugin: WooCommerce Shipment Tracking
- Adds 'Tracking Number' metabox to order edit page
- Stores: _tracking_number meta field
- Current: ❌ NOT visible in WooNooW admin
- Expected: ✅ Should be visible and editable

**Impact:**
1. Breaks compatibility with popular plugins
2. Users cannot see/edit custom fields
3. Data exists but not accessible in SPA
4. Forces users back to classic admin
5. BLOCKS production readiness

**Solution Architecture:**

Phase 1: API Layer (2-3 days)
- Expose meta_data in OrdersController::show()
- Expose meta_data in ProductsController::get_product()
- Add filters: woonoow/order_api_data, woonoow/product_api_data
- Add filters: woonoow/order_allowed_private_meta
- Add actions: woonoow/order_updated, woonoow/product_updated

Phase 2: Frontend Components (3-4 days)
- Create MetaFields.tsx component
- Create useMetaFields.ts hook
- Update Orders/Edit.tsx to include meta fields
- Update Products/Edit.tsx to include meta fields
- Add meta fields to detail pages

Phase 3: Plugin Integration (2-3 days)
- Create MetaFieldsRegistry.php
- Add woonoow/register_meta_fields action
- Localize fields to JavaScript
- Create example: ShipmentTracking.php integration
- Document integration pattern

**Documentation Created:**
- METABOX_COMPAT.md - Complete implementation guide
- Includes code examples for all phases
- Includes third-party integration guide
- Includes testing checklist

**Updated:**
- PROJECT_SOP.md - Added metabox compat reference
- Marked as CRITICAL requirement
- Noted as blocking production readiness

**Timeline:**
Total: 1-2 weeks implementation

**Blocking:**
- ✅ Coupons CRUD (can proceed)
- ✅ Customers CRUD (can proceed)
- ❌ Production readiness (BLOCKED)

**Next Steps:**
1. Review METABOX_COMPAT.md
2. Prioritize implementation
3. Start with Phase 1 (API layer)
4. Test with popular plugins (Shipment Tracking, ACF)

METABOX_COMPAT.md

@@ -0,0 +1,552 @@
+# WooNooW Metabox & Custom Fields Compatibility
+
+## Current Status: ❌ NOT IMPLEMENTED
+
+**Critical Gap:** Our SPA admin does NOT currently expose custom meta fields, metaboxes, or third-party plugin data injected via WordPress/WooCommerce hooks.
+
+### Example Use Case:
+```
+Plugin: WooCommerce Shipment Tracking
+- Adds "Tracking Number" metabox to order edit page
+- Uses: add_meta_box('wc_shipment_tracking', ...)
+- Stores: update_post_meta($order_id, '_tracking_number', $value)
+
+Current Behavior: ❌ Field NOT visible in WooNooW admin
+Expected Behavior: ✅ Field should be visible and editable
+```
+
+---
+
+## Problem Analysis
+
+### 1. Orders API (`OrdersController.php`)
+
+**Current Implementation:**
+```php
+public static function show(WP_REST_Request $req) {
+    $order = wc_get_order($id);
+    
+    $data = [
+        'id' => $order->get_id(),
+        'status' => $order->get_status(),
+        'billing' => [...],
+        'shipping' => [...],
+        'items' => [...],
+        // ... hardcoded fields only
+    ];
+    
+    return new WP_REST_Response($data, 200);
+}
+```
+
+**Missing:**
+- ❌ No `get_meta_data()` exposure
+- ❌ No `apply_filters('woonoow/order_data', $data, $order)`
+- ❌ No metabox hook listening
+- ❌ No custom field groups
+
+### 2. Products API (`ProductsController.php`)
+
+**Current Implementation:**
+```php
+public static function get_product(WP_REST_Request $request) {
+    $product = wc_get_product($id);
+    
+    return new WP_REST_Response([
+        'id' => $product->get_id(),
+        'name' => $product->get_name(),
+        // ... hardcoded fields only
+    ], 200);
+}
+```
+
+**Missing:**
+- ❌ No custom product meta exposure
+- ❌ No `apply_filters('woonoow/product_data', $data, $product)`
+- ❌ No ACF/CMB2/Pods integration
+- ❌ No custom tabs/panels
+
+---
+
+## Solution Architecture
+
+### Phase 1: Meta Data Exposure (API Layer)
+
+#### 1.1 Orders API Enhancement
+
+**Add to `OrdersController::show()`:**
+```php
+public static function show(WP_REST_Request $req) {
+    $order = wc_get_order($id);
+    
+    // ... existing data ...
+    
+    // Expose all meta data
+    $meta_data = [];
+    foreach ($order->get_meta_data() as $meta) {
+        $key = $meta->key;
+        
+        // Skip internal/private meta (starts with _)
+        // unless explicitly allowed
+        if (strpos($key, '_') === 0) {
+            $allowed_private = apply_filters('woonoow/order_allowed_private_meta', [
+                '_tracking_number',
+                '_tracking_provider',
+                '_shipment_tracking_items',
+                '_wc_shipment_tracking_items',
+                // Add more as needed
+            ], $order);
+            
+            if (!in_array($key, $allowed_private, true)) {
+                continue;
+            }
+        }
+        
+        $meta_data[$key] = $meta->value;
+    }
+    
+    $data['meta'] = $meta_data;
+    
+    // Allow plugins to add/modify data
+    $data = apply_filters('woonoow/order_api_data', $data, $order, $req);
+    
+    return new WP_REST_Response($data, 200);
+}
+```
+
+**Add to `OrdersController::update()`:**
+```php
+public static function update(WP_REST_Request $req) {
+    $order = wc_get_order($id);
+    $data = $req->get_json_params();
+    
+    // ... existing update logic ...
+    
+    // Update custom meta fields
+    if (isset($data['meta']) && is_array($data['meta'])) {
+        foreach ($data['meta'] as $key => $value) {
+            // Validate meta key is allowed
+            $allowed = apply_filters('woonoow/order_updatable_meta', [
+                '_tracking_number',
+                '_tracking_provider',
+                // Add more as needed
+            ], $order);
+            
+            if (in_array($key, $allowed, true)) {
+                $order->update_meta_data($key, $value);
+            }
+        }
+    }
+    
+    $order->save();
+    
+    // Allow plugins to perform additional updates
+    do_action('woonoow/order_updated', $order, $data, $req);
+    
+    return new WP_REST_Response(['success' => true], 200);
+}
+```
+
+#### 1.2 Products API Enhancement
+
+**Add to `ProductsController::get_product()`:**
+```php
+public static function get_product(WP_REST_Request $request) {
+    $product = wc_get_product($id);
+    
+    // ... existing data ...
+    
+    // Expose all meta data
+    $meta_data = [];
+    foreach ($product->get_meta_data() as $meta) {
+        $key = $meta->key;
+        
+        // Skip internal meta unless allowed
+        if (strpos($key, '_') === 0) {
+            $allowed_private = apply_filters('woonoow/product_allowed_private_meta', [
+                '_custom_field_example',
+                // Add more as needed
+            ], $product);
+            
+            if (!in_array($key, $allowed_private, true)) {
+                continue;
+            }
+        }
+        
+        $meta_data[$key] = $meta->value;
+    }
+    
+    $data['meta'] = $meta_data;
+    
+    // Allow plugins to add/modify data
+    $data = apply_filters('woonoow/product_api_data', $data, $product, $request);
+    
+    return new WP_REST_Response($data, 200);
+}
+```
+
+---
+
+### Phase 2: Frontend Rendering (React Components)
+
+#### 2.1 Dynamic Meta Fields Component
+
+**Create: `admin-spa/src/components/MetaFields.tsx`**
+```tsx
+interface MetaField {
+  key: string;
+  label: string;
+  type: 'text' | 'textarea' | 'number' | 'select' | 'date';
+  options?: Array<{value: string; label: string}>;
+  section?: string; // Group fields into sections
+}
+
+interface MetaFieldsProps {
+  meta: Record<string, any>;
+  fields: MetaField[];
+  onChange: (key: string, value: any) => void;
+  readOnly?: boolean;
+}
+
+export function MetaFields({ meta, fields, onChange, readOnly }: MetaFieldsProps) {
+  // Group fields by section
+  const sections = fields.reduce((acc, field) => {
+    const section = field.section || 'Other';
+    if (!acc[section]) acc[section] = [];
+    acc[section].push(field);
+    return acc;
+  }, {} as Record<string, MetaField[]>);
+  
+  return (
+    <div className="space-y-6">
+      {Object.entries(sections).map(([section, sectionFields]) => (
+        <Card key={section}>
+          <CardHeader>
+            <CardTitle>{section}</CardTitle>
+          </CardHeader>
+          <CardContent className="space-y-4">
+            {sectionFields.map(field => (
+              <div key={field.key}>
+                <Label>{field.label}</Label>
+                {field.type === 'text' && (
+                  <Input
+                    value={meta[field.key] || ''}
+                    onChange={(e) => onChange(field.key, e.target.value)}
+                    disabled={readOnly}
+                  />
+                )}
+                {field.type === 'textarea' && (
+                  <Textarea
+                    value={meta[field.key] || ''}
+                    onChange={(e) => onChange(field.key, e.target.value)}
+                    disabled={readOnly}
+                  />
+                )}
+                {/* Add more field types as needed */}
+              </div>
+            ))}
+          </CardContent>
+        </Card>
+      ))}
+    </div>
+  );
+}
+```
+
+#### 2.2 Hook System for Field Registration
+
+**Create: `admin-spa/src/hooks/useMetaFields.ts`**
+```tsx
+interface MetaFieldsRegistry {
+  orders: MetaField[];
+  products: MetaField[];
+}
+
+// Global registry (can be extended by plugins via window object)
+declare global {
+  interface Window {
+    WooNooWMetaFields?: MetaFieldsRegistry;
+  }
+}
+
+export function useMetaFields(type: 'orders' | 'products'): MetaField[] {
+  const [fields, setFields] = useState<MetaField[]>([]);
+  
+  useEffect(() => {
+    // Get fields from global registry
+    const registry = window.WooNooWMetaFields || { orders: [], products: [] };
+    setFields(registry[type] || []);
+  }, [type]);
+  
+  return fields;
+}
+```
+
+#### 2.3 Integration in Order Edit Form
+
+**Update: `admin-spa/src/routes/Orders/Edit.tsx`**
+```tsx
+import { MetaFields } from '@/components/MetaFields';
+import { useMetaFields } from '@/hooks/useMetaFields';
+
+export default function OrderEdit() {
+  const { id } = useParams();
+  const metaFields = useMetaFields('orders');
+  
+  const orderQ = useQuery({
+    queryKey: ['order', id],
+    queryFn: () => api.get(`/orders/${id}`),
+  });
+  
+  const [formData, setFormData] = useState({
+    // ... existing fields ...
+    meta: {},
+  });
+  
+  useEffect(() => {
+    if (orderQ.data) {
+      setFormData(prev => ({
+        ...prev,
+        meta: orderQ.data.meta || {},
+      }));
+    }
+  }, [orderQ.data]);
+  
+  const handleMetaChange = (key: string, value: any) => {
+    setFormData(prev => ({
+      ...prev,
+      meta: {
+        ...prev.meta,
+        [key]: value,
+      },
+    }));
+  };
+  
+  return (
+    <div>
+      {/* Existing order form fields */}
+      
+      {/* Custom meta fields */}
+      {metaFields.length > 0 && (
+        <MetaFields
+          meta={formData.meta}
+          fields={metaFields}
+          onChange={handleMetaChange}
+        />
+      )}
+    </div>
+  );
+}
+```
+
+---
+
+### Phase 3: Plugin Integration Layer
+
+#### 3.1 PHP Hook for Field Registration
+
+**Create: `includes/Compat/MetaFieldsRegistry.php`**
+```php
+<?php
+namespace WooNooW\Compat;
+
+class MetaFieldsRegistry {
+    
+    private static $order_fields = [];
+    private static $product_fields = [];
+    
+    public static function init() {
+        add_action('admin_enqueue_scripts', [__CLASS__, 'localize_fields']);
+        
+        // Allow plugins to register fields
+        do_action('woonoow/register_meta_fields');
+    }
+    
+    /**
+     * Register order meta field
+     */
+    public static function register_order_field($key, $args = []) {
+        $defaults = [
+            'key' => $key,
+            'label' => ucfirst(str_replace('_', ' ', $key)),
+            'type' => 'text',
+            'section' => 'Other',
+        ];
+        
+        self::$order_fields[$key] = array_merge($defaults, $args);
+    }
+    
+    /**
+     * Register product meta field
+     */
+    public static function register_product_field($key, $args = []) {
+        $defaults = [
+            'key' => $key,
+            'label' => ucfirst(str_replace('_', ' ', $key)),
+            'type' => 'text',
+            'section' => 'Other',
+        ];
+        
+        self::$product_fields[$key] = array_merge($defaults, $args);
+    }
+    
+    /**
+     * Localize fields to JavaScript
+     */
+    public static function localize_fields() {
+        if (!is_admin()) return;
+        
+        wp_localize_script('woonoow-admin', 'WooNooWMetaFields', [
+            'orders' => array_values(self::$order_fields),
+            'products' => array_values(self::$product_fields),
+        ]);
+    }
+}
+```
+
+#### 3.2 Example: Shipment Tracking Integration
+
+**Create: `includes/Compat/Integrations/ShipmentTracking.php`**
+```php
+<?php
+namespace WooNooW\Compat\Integrations;
+
+use WooNooW\Compat\MetaFieldsRegistry;
+
+class ShipmentTracking {
+    
+    public static function init() {
+        // Only load if WC Shipment Tracking is active
+        if (!class_exists('WC_Shipment_Tracking')) {
+            return;
+        }
+        
+        add_action('woonoow/register_meta_fields', [__CLASS__, 'register_fields']);
+        add_filter('woonoow/order_allowed_private_meta', [__CLASS__, 'allow_meta']);
+        add_filter('woonoow/order_updatable_meta', [__CLASS__, 'allow_meta']);
+    }
+    
+    public static function register_fields() {
+        MetaFieldsRegistry::register_order_field('_tracking_number', [
+            'label' => __('Tracking Number', 'woonoow'),
+            'type' => 'text',
+            'section' => 'Shipment Tracking',
+        ]);
+        
+        MetaFieldsRegistry::register_order_field('_tracking_provider', [
+            'label' => __('Tracking Provider', 'woonoow'),
+            'type' => 'select',
+            'section' => 'Shipment Tracking',
+            'options' => [
+                ['value' => 'jne', 'label' => 'JNE'],
+                ['value' => 'jnt', 'label' => 'J&T'],
+                ['value' => 'sicepat', 'label' => 'SiCepat'],
+            ],
+        ]);
+    }
+    
+    public static function allow_meta($allowed) {
+        $allowed[] = '_tracking_number';
+        $allowed[] = '_tracking_provider';
+        $allowed[] = '_shipment_tracking_items';
+        return $allowed;
+    }
+}
+```
+
+---
+
+## Implementation Checklist
+
+### Phase 1: API Layer ✅
+- [ ] Add meta data exposure to `OrdersController::show()`
+- [ ] Add meta data update to `OrdersController::update()`
+- [ ] Add meta data exposure to `ProductsController::get_product()`
+- [ ] Add meta data update to `ProductsController::update_product()`
+- [ ] Add filters: `woonoow/order_api_data`, `woonoow/product_api_data`
+- [ ] Add filters: `woonoow/order_allowed_private_meta`, `woonoow/order_updatable_meta`
+- [ ] Add actions: `woonoow/order_updated`, `woonoow/product_updated`
+
+### Phase 2: Frontend Components ✅
+- [ ] Create `MetaFields.tsx` component
+- [ ] Create `useMetaFields.ts` hook
+- [ ] Update `Orders/Edit.tsx` to include meta fields
+- [ ] Update `Orders/View.tsx` to display meta fields (read-only)
+- [ ] Update `Products/Edit.tsx` to include meta fields
+- [ ] Add meta fields to Order/Product detail pages
+
+### Phase 3: Plugin Integration ✅
+- [ ] Create `MetaFieldsRegistry.php`
+- [ ] Add `woonoow/register_meta_fields` action
+- [ ] Localize fields to JavaScript
+- [ ] Create example integration: `ShipmentTracking.php`
+- [ ] Document integration pattern for third-party devs
+
+### Phase 4: Testing ✅
+- [ ] Test with WooCommerce Shipment Tracking plugin
+- [ ] Test with ACF (Advanced Custom Fields)
+- [ ] Test with CMB2 (Custom Metaboxes 2)
+- [ ] Test with custom metabox plugins
+- [ ] Test meta data save/update
+- [ ] Test meta data display in detail view
+
+---
+
+## Third-Party Plugin Integration Guide
+
+### For Plugin Developers:
+
+**Example: Adding custom fields to WooNooW admin**
+
+```php
+// In your plugin file
+add_action('woonoow/register_meta_fields', function() {
+    // Register order field
+    WooNooW\Compat\MetaFieldsRegistry::register_order_field('_my_custom_field', [
+        'label' => __('My Custom Field', 'my-plugin'),
+        'type' => 'text',
+        'section' => 'My Plugin',
+    ]);
+    
+    // Register product field
+    WooNooW\Compat\MetaFieldsRegistry::register_product_field('_my_product_field', [
+        'label' => __('My Product Field', 'my-plugin'),
+        'type' => 'textarea',
+        'section' => 'My Plugin',
+    ]);
+});
+
+// Allow meta to be read/written
+add_filter('woonoow/order_allowed_private_meta', function($allowed) {
+    $allowed[] = '_my_custom_field';
+    return $allowed;
+});
+
+add_filter('woonoow/order_updatable_meta', function($allowed) {
+    $allowed[] = '_my_custom_field';
+    return $allowed;
+});
+```
+
+---
+
+## Priority
+
+**Status:** 🔴 **CRITICAL - MUST IMPLEMENT**
+
+**Why:**
+1. Breaks compatibility with popular plugins (Shipment Tracking, ACF, etc.)
+2. Users cannot see/edit custom fields added by other plugins
+3. Data exists in database but not accessible in SPA admin
+4. Forces users to switch back to classic admin for custom fields
+
+**Timeline:**
+- Phase 1 (API): 2-3 days
+- Phase 2 (Frontend): 3-4 days
+- Phase 3 (Integration): 2-3 days
+- **Total: ~1-2 weeks**
+
+**Blocking:**
+- Coupons CRUD (can proceed)
+- Customers CRUD (can proceed)
+- **Production readiness** (BLOCKED until this is done)

PROJECT_SOP.md

@@ -33,6 +33,12 @@ WooNooW modernizes WooCommerce **without migration**, delivering a Hybrid + SPA
 - Prevents route conflicts between modules
 - Documents ownership and naming conventions
 
+**Metabox & Custom Fields compatibility:**
+- `METABOX_COMPAT.md` - 🔴 **CRITICAL** compatibility requirement
+- Documents how to expose WordPress/WooCommerce metaboxes in SPA
+- **Currently NOT implemented** - blocks production readiness
+- Required for third-party plugin compatibility (Shipment Tracking, ACF, etc.)
+
 **Documentation Rules:**
 1. ✅ Update `PROGRESS_NOTE.md` after completing any major feature
 2. ✅ Add test cases to `TESTING_CHECKLIST.md` before implementation