docs: document coupon constraints and pivot/FK conventions

Note the coupon creator FKs and the three scoping pivots' foreign-key and
unique rules in the schema doc, add migration/multi-select conventions to
AGENTS.md, and mark Coupons done in IMPLEMENTATION.md.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: bahman026

admin/AGENTS.md

@@ -199,6 +199,7 @@ When adding a new entity, build the files in this order, matching the existing f
 - Select fields backed by an enum use `->options(SomeEnum::options())` and `->default(SomeEnum::CASE->value)`.
 - Table text columns that can be long (headings, relation labels) use `->limit(30)->wrap()`.
 - Enum-backed table columns render via `->getStateUsing(fn ($record) => $record->field->label())` and `->color(fn ($record) => $record->field->color())`.
+- Manage many-to-many pivots with a relationship multi-select: `Select::make('products')->relationship('products', 'heading')->multiple()->searchable()->preload()` (see `CouponResource`). No separate resource for pure scoping pivots.
 
 ## Models
 
@@ -218,7 +219,9 @@ When adding a new entity, build the files in this order, matching the existing f
 ## Migrations
 
 - Anonymous class style: `return new class extends Migration`.
-- Use `$table->foreignIdFor(Model::class)` for foreign keys (add `->nullable()` when optional).
+- Use `$table->foreignIdFor(Model::class)` for foreign keys (add `->nullable()` when optional). Chain `->constrained()->cascadeOnDelete()` / `->nullOnDelete()` / `->restrictOnDelete()` to add the real FK constraint with its delete rule.
+- For a second FK to the same table, use a named column: `$table->foreignId('user_creator_id')->nullable()->constrained('users')->nullOnDelete()` (see `coupons`).
+- Pivot tables add `$table->unique([...])` on the key pair and `->cascadeOnDelete()` on both FKs (see `coupon_product`).
 - Default enum columns to a case value: `$table->unsignedTinyInteger('status')->default(ProductStatusEnum::PUBLISHED->value);`.
 - Always implement `down()` with `Schema::dropIfExists(...)`.
 

admin/IMPLEMENTATION.md

@@ -22,6 +22,7 @@ Catalog layer and platform basics.
 - [x] Products (+ `product_attribute` pivot, product images)
 - [x] Varieties (+ `variety_counts` auto-sync on Product)
 - [x] Discounts (auto-applied price rules per variety)
+- [x] Coupons (+ `coupon_product`, `coupon_variety`, `category_coupon` scoping pivots)
 - [x] Images (polymorphic, used via uploads - no standalone resource by design)
 - [~] Addresses (model only, no resource yet)
 

admin/ShoFlow db doc.md

@@ -163,8 +163,9 @@ This table stores cards.
 
 Scopes a coupon so it applies only to products in specific categories.
 
-* `category_id` specifies the category the coupon is allowed for.  
-* `coupon_id` specifies the coupon this scope belongs to.
+* `category_id` specifies the category the coupon is allowed for. Foreign key; cascades on category delete.  
+* `coupon_id` specifies the coupon this scope belongs to. Foreign key; cascades on coupon delete.  
+* The pair `(category_id, coupon_id)` is unique.
 
 # cities
 
@@ -184,9 +185,9 @@ Stores discount coupons. Unlike discounts, a coupon is applied manually: the cus
 * `max_discount`: The maximum discount amount the coupon can give.  
 * `total_used`: How many times this coupon has already been used.  
 * `total_uses`: How many times this coupon is allowed to be used in total.  
-* `user_id`: Limits usage to a specific user.  
-* `user_creator_id`: The admin user who created the coupon, if created by an admin.  
-* `seller_creator_id`: The seller who created the coupon, if created by a seller.  
+* `user_id`: Limits usage to a specific user. Nullable foreign key to `users`; set to null when the user is deleted.  
+* `user_creator_id`: The admin user who created the coupon, if created by an admin. Nullable foreign key to `users`.  
+* `seller_creator_id`: The seller who created the coupon, if created by a seller. Nullable foreign key to `users`.  
 * `status`: Has states "active" (default, usable), "canceled", "used", and "under review".  
 * `is_percent`: Indicates if the discount is a percentage or a fixed amount.  
 * `shipping`: Indicates if this coupon includes free shipping (applies only to free shipping, not to the price).  
@@ -197,14 +198,16 @@ Stores discount coupons. Unlike discounts, a coupon is applied manually: the cus
 # coupon\_product
 
 * Scopes a coupon so it can only be applied to certain products.  
-* `coupon_id`: The coupon this scope belongs to.  
-* `product_id`: A product the coupon is allowed for.
+* `coupon_id`: The coupon this scope belongs to. Foreign key; cascades on coupon delete.  
+* `product_id`: A product the coupon is allowed for. Foreign key; cascades on product delete.  
+* The pair `(coupon_id, product_id)` is unique.
 
 # coupon\_variety
 
 * Scopes a coupon so it applies to certain varieties only, useful for sellers who want a coupon for some of their varieties.  
-* `coupon_id`: The coupon this scope belongs to.  
-* `variety_id`: A variety the coupon is allowed for.
+* `coupon_id`: The coupon this scope belongs to. Foreign key; cascades on coupon delete.  
+* `variety_id`: A variety the coupon is allowed for. Foreign key; cascades on variety delete.  
+* The pair `(coupon_id, variety_id)` is unique.
 
 # discounts