Fix addon checkout item field parsing

[ArnavBallinCode]

Summary by Sourcery

Bug Fixes:

• Fix addon selection parsing by supporting both _item_ and legacy _product_ POST parameter formats for quantities and prices.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adjusts add-on checkout parsing to support both new item POST field names and legacy product names when extracting quantity and price for non-variation add-ons.

Sequence diagram for updated add-on item field parsing

sequenceDiagram
    participant Request
    participant AddOnsStep
    participant POSTData

    Request->>AddOnsStep: call _clean_category(form, category)
    loop non_variation_addon_items
        AddOnsStep->>AddOnsStep: build item_key
        AddOnsStep->>AddOnsStep: build legacy_product_key

        AddOnsStep->>POSTData: get item_key
        POSTData-->>AddOnsStep: quantity_or_none
        AddOnsStep->>POSTData: get legacy_product_key (fallback)
        POSTData-->>AddOnsStep: legacy_quantity_or_none
        AddOnsStep->>AddOnsStep: val = int(item_quantity or legacy_quantity or 0)

        AddOnsStep->>POSTData: get item_key_price
        POSTData-->>AddOnsStep: price_or_none
        AddOnsStep->>POSTData: get legacy_product_key_price (fallback)
        POSTData-->>AddOnsStep: legacy_price_or_none
        AddOnsStep->>AddOnsStep: price = item_price or legacy_price or 0

        AddOnsStep->>AddOnsStep: if val > 0: selected[i, None] = (val, price)
    end
    AddOnsStep-->>Request: cleaned category selections

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File-Level Changes

Change	Details	Files
Update POST field parsing for non-variation add-ons to be backward compatible with both new and legacy field name conventions.	Replace use of product POST key prefix with item for the primary lookup when reading add-on quantity and price. Introduce fallback to legacy product POST keys when item keys are absent for both quantity and price. Ensure the selected add-on entries are still only stored when a non-zero quantity is provided.	app/eventyay/presale/checkoutflowstep/add_ons_step.py

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[sourcery-ai]

Hey - I've left some high level feedback:

• Consider extracting the repeated POST key lookup logic for val and price into a small helper to reduce duplication and make the precedence between _item_ and _product_ keys clearer.
• It might be worth adding a brief code comment explaining that _item_ is the new format and _product_ is kept for backward compatibility, so future maintainers understand why both are checked.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider extracting the repeated POST key lookup logic for `val` and `price` into a small helper to reduce duplication and make the precedence between `_item_` and `_product_` keys clearer.
- It might be worth adding a brief code comment explaining that `_item_` is the new format and `_product_` is kept for backward compatibility, so future maintainers understand why both are checked.

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[Copilot]

Pull request overview

Fixes a mismatch between the add-on checkout form field names and the backend parsing logic in the presale checkout flow, so selected add-ons without variations are correctly recognized during checkout.

Changes:

• Update add-on quantity parsing to read cp_<cartpos>_item_<item_id> (current template/test format).
• Add backward-compatible fallback to the legacy cp_<cartpos>_product_<item_id> field name for both quantity and free-price fields.

[Saksham-Sirohi]

LGTM