# Skill Contract

**Skill ID:** update_cart_item
**Version:** v1
**Status:** APPROVED

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## Intent
To enable users to update the quantity of a specific product that is currently in their e-member shopping cart, providing immediate feedback on the operation's outcome.

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## Inputs
- `product_id`: The unique identifier (product code) of the item whose quantity needs to be updated in the cart. (required)
- `new_quantity`: The desired new quantity for the specified product in the cart. Must be a positive integer. (required)

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## Outputs
- `message`: A string indicating whether the quantity update was successful or if it failed, including an error message if applicable.

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## Output Message
"Quantity is successfully updated." or "Failed to update quantity. Reason: [Error Message from Tool]"

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## Logic
1. Receive `product_id` and `new_quantity` as inputs.
2. Call the `update_cart` MCP tool with the following parameters:
    - `cart_procode`: Map from input `product_id`.
    - `cart_item_qty`: Map from input `new_quantity`.
3. Await the response from the `update_cart` tool.
4. Check the `error.status` field in the tool's API response envelope.
5. If `error.status` is `False` (indicating success):
    - Return the output message: "Quantity is successfully updated."
6. If `error.status` is `True` (indicating failure):
    - Extract the `error.msg` from the tool's response.
    - Return the output message: "Failed to update quantity. Reason: [error.msg]".

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## Additional Logic
The skill robustly handles the response from the `update_cart` MCP tool, distinguishing between success and various failure scenarios indicated by the tool's error object, and constructs a user-friendly message accordingly.

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## Side Effects
- Modifies the user's shopping cart state in the Century e-member system by updating the quantity of a specified product.
- Calls the external `update_cart` API.

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## Capability Summary
Updates the quantity of a specified product within the user's e-member shopping cart using the `update_cart` MCP tool, and reports the outcome.

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## Allowed Roles
- SUPERUSER
- Customer Service Representative
- Authenticated User

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## Assumptions
- The provided `product_id` corresponds to a valid product code recognized by the Century e-member system.
- The user has an active shopping cart session and the `product_id` is already present in their cart (if not, the `update_cart` tool's behavior will dictate the outcome).
- The `new_quantity` is a positive integer value suitable for a product quantity.
- The `update_cart` MCP tool is operational and accessible.

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## Non-Goals
- Adding a new product to the shopping cart if it's not already present.
- Removing a product from the shopping cart.
- Validating the stock availability of the product before updating the quantity.
- Handling authentication or session management for the e-member system directly; this is assumed to be handled by the underlying `update_cart` tool's context.

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## Failure Modes
- **Tool Execution Failure:** The `update_cart` MCP tool itself fails to execute due to internal errors or unavailability.
- **API Error Response:** The `update_cart` tool returns an error status (`error.status: True`) from the underlying API, possibly due to:
    - Invalid `product_id` (e.g., product not found in cart, or invalid format).
    - Invalid `new_quantity` (e.g., negative, zero, or exceeding maximum allowed quantity).
    - Backend system errors during cart update.
    - Session or authentication issues preventing cart modification.
- **Network/Connectivity Issues:** Inability to communicate with the `update_cart` tool.

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## Data & System Access
- **MCP Tool Access:** `update_cart`
- **External System:** Century e-member shopping cart system (via `update_cart` tool)
- **Data Modified:** User's shopping cart data (product quantities)

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## Safety & Risk
Risk Level: MEDIUM

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## Approval

    Approved by: USER  
    Approved on: 2026-05-06T12:33:47.575177Z