Checkout hooks

Five frozen decision points on the checkout path (ADR 0020 §4). A hook is a pure function f(CartSnapshot, config) → HookOp[]: JSON in, a closed union of operations out — no I/O, no SQL, no fetch. The platform applies the ops with clamps; a throwing or over-budget hook fails OPEN (pricing/shipping/payment.filter) and trips a breaker after 5 consecutive failures (extension.hook.deactivate, one-click re-enable).

Budgets: snapshot ≤ 128 KB, ops ≤ 20 KB.

`checkout.cart.validate`

Allowed ops (JSON Schema):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "maxItems": 50,
  "type": "array",
  "items": {
    "oneOf": [
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "reject"
          },
          "code": {
            "type": "string",
            "pattern": "^[a-z0-9_]{2,40}$"
          },
          "messageCode": {
            "type": "string",
            "pattern": "^[a-z0-9_]{2,40}$"
          },
          "lineId": {
            "type": "string",
            "maxLength": 16
          }
        },
        "required": [
          "op",
          "code",
          "messageCode"
        ],
        "additionalProperties": false
      },
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "capQty"
          },
          "lineId": {
            "type": "string",
            "maxLength": 16
          },
          "qty": {
            "type": "integer",
            "minimum": 1,
            "maximum": 99
          }
        },
        "required": [
          "op",
          "lineId",
          "qty"
        ],
        "additionalProperties": false
      }
    ]
  }
}

`checkout.pricing.adjust`

Allowed ops (JSON Schema):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "maxItems": 50,
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "op": {
        "type": "string",
        "const": "addDiscount"
      },
      "lineId": {
        "type": "string",
        "maxLength": 16
      },
      "kurus": {
        "type": "integer",
        "minimum": 0,
        "maximum": 10000000000000
      },
      "label": {
        "type": "string",
        "minLength": 1,
        "maxLength": 60
      }
    },
    "required": [
      "op",
      "kurus",
      "label"
    ],
    "additionalProperties": false
  }
}

`checkout.shipping.rates`

Allowed ops (JSON Schema):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "maxItems": 50,
  "type": "array",
  "items": {
    "oneOf": [
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "addRate"
          },
          "id": {
            "type": "string",
            "pattern": "^[a-z0-9_-]{1,32}$"
          },
          "labelTR": {
            "type": "string",
            "minLength": 1,
            "maxLength": 60
          },
          "kurus": {
            "type": "integer",
            "minimum": 0,
            "maximum": 10000000000000
          },
          "etaDays": {
            "type": "array",
            "prefixItems": [
              {
                "type": "integer",
                "minimum": 0,
                "maximum": 60
              },
              {
                "type": "integer",
                "minimum": 0,
                "maximum": 60
              }
            ]
          }
        },
        "required": [
          "op",
          "id",
          "labelTR",
          "kurus"
        ],
        "additionalProperties": false
      },
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "filterRate"
          },
          "id": {
            "type": "string",
            "pattern": "^[a-z0-9_-]{1,32}$"
          }
        },
        "required": [
          "op",
          "id"
        ],
        "additionalProperties": false
      },
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "renameRate"
          },
          "id": {
            "type": "string",
            "pattern": "^[a-z0-9_-]{1,32}$"
          },
          "labelTR": {
            "type": "string",
            "minLength": 1,
            "maxLength": 60
          }
        },
        "required": [
          "op",
          "id",
          "labelTR"
        ],
        "additionalProperties": false
      }
    ]
  }
}

`checkout.payment.filter`

Allowed ops (JSON Schema):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "maxItems": 50,
  "type": "array",
  "items": {
    "oneOf": [
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "exclude"
          },
          "methodId": {
            "type": "string",
            "pattern": "^[a-z0-9_]{2,32}$"
          }
        },
        "required": [
          "op",
          "methodId"
        ],
        "additionalProperties": false
      },
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "reorder"
          },
          "order": {
            "maxItems": 10,
            "type": "array",
            "items": {
              "type": "string",
              "pattern": "^[a-z0-9_]{2,32}$"
            }
          }
        },
        "required": [
          "op",
          "order"
        ],
        "additionalProperties": false
      },
      {
        "type": "object",
        "properties": {
          "op": {
            "type": "string",
            "const": "capTaksit"
          },
          "methodId": {
            "type": "string",
            "pattern": "^[a-z0-9_]{2,32}$"
          },
          "max": {
            "type": "integer",
            "minimum": 1,
            "maximum": 12
          }
        },
        "required": [
          "op",
          "methodId",
          "max"
        ],
        "additionalProperties": false
      }
    ]
  }
}

`checkout.order.validate`

Allowed ops (JSON Schema):

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "maxItems": 50,
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "op": {
        "type": "string",
        "const": "reject"
      },
      "code": {
        "type": "string",
        "pattern": "^[a-z0-9_]{2,40}$"
      },
      "messageCode": {
        "type": "string",
        "pattern": "^[a-z0-9_]{2,40}$"
      }
    },
    "required": [
      "op",
      "code",
      "messageCode"
    ],
    "additionalProperties": false
  }
}

Shopper-facing message codes

Hooks never emit prose; they emit codes the platform maps to Turkish:

code	TR
`out_of_stock`	Üründe yeterli stok yok.
`insufficient_stock`	Stok, istediğin adet için yeterli değil.
`qty_capped`	Bu ürün için adet sınırına ulaşıldı.
`line_unavailable`	Ürün artık satışta değil ve sepetten çıkarıldı.
`price_changed`	Fiyat güncellendi — lütfen yeni tutarı kontrol et.
`shipping_unavailable`	Bu adrese şu anda kargo yapılamıyor.
`payment_unavailable`	Şu anda ödeme alınamıyor — lütfen daha sonra tekrar dene.
`digital_kapida_disallowed`	Dijital ürünler kapıda ödeme ile satın alınamaz.
`session_expired`	Oturumun zaman aşımına uğradı.
`amount_mismatch`	Ödeme tutarı doğrulanamadı — sipariş oluşturulmadı, kartından çekim yapıldıysa iade edilir.
`order_rejected`	Sipariş şu anda oluşturulamıyor.
`checkout_disabled`	Bu mağazada ödeme yakında açılıyor.
`cart_empty`	Sepetin boş.

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