fix(woocommerce): persist custom meta on new product first save

[dkoo]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

Fixes a bug where Newspack's custom product options (e.g., Group subscription enabled flag and member limit) were silently dropped on the first save of a brand-new product whose type was being changed via the product-type dropdown (e.g., new product → "Simple subscription"). Subsequent edits to existing products were unaffected.

Root cause: Both WooCommerce_Products::save_custom_product_options and WC core's WC_Meta_Box_Product_Data::save are hooked on woocommerce_process_product_meta at priority 10, so the order depends on registration timing. Newspack registers first, which means at the moment our handler runs, $product->get_type() still returns the auto-draft default (simple) — WC hasn't yet updated the product-type term. Our type-filter at class-woocommerce-products.php:289 then skips options whose product_types list doesn't include simple (Group subscription requires subscription or subscription_variation).

Fix: Read the product type from $_POST['product-type'] as the source of truth, falling back to $product->get_type() when not present (REST, programmatic saves). Mirrors WC core's own pattern in WC_Meta_Box_Product_Data::save().

Closes NPPD-1485.

How to test the changes in this Pull Request:

1. Set define( 'NEWSPACK_CONTENT_GATES', true ); in wp-config.php so the Group subscription option is registered.
2. Ensure WooCommerce + WooCommerce Subscriptions are active.
3. Simple subscription, first save (the bug):
   1. Go to Products → Add New.
   2. Set product title, choose product type "Simple subscription", set a subscription price.
   3. Tick Group subscription and set Group subscription member limit to e.g. 5.
   4. Click Save Draft.
   5. ✅ Reload the product — Group subscription should still be enabled and the limit preserved. Pre-fix: both values were lost.
4. Existing-product edit (no regression):
   1. Open the product saved in step 3.
   2. Change the limit to a different value, click Update.
   3. ✅ The new value persists.
5. Variable subscription parent + variations (untouched code path):
   1. Products → Add New, set type to Variable subscription, save draft.
   2. Add an attribute (used for variations), generate variations.
   3. Expand a variation, set subscription price and tick Group subscription, set a limit.
   4. Save changes.
   5. ✅ Variation persists Group subscription meta on its first save (this code path was already correct — verified in review).
6. Programmatic / REST save (out of scope): REST API (POST /wp-json/wc/v3/products) and the new WC product block editor bypass woocommerce_process_product_meta entirely and are not covered by this PR. To be tracked in a follow-up.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable? — Deferred: extending the existing WC_Product mock at tests/mocks/wc-mocks.php (no update_meta_data/save/get_status/get_date_*) is out of scope for this hotfix. Verified empirically against a live env. Follow-up ticket recommended.
• Have you successfully ran tests with your changes locally? — n test-php: 924 tests, 2859 assertions, all passing.

[github-actions]

🎉 This PR is included in version 6.39.4-hotfix-nppd-1485-group-subscription-meta-unsaved-product.1 🎉

The release is available on GitHub release

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Pull request overview

Fixes WooCommerce admin “first save” behavior where Newspack custom product options could be dropped when creating a new product and changing its type via the product-type dropdown (due to hook ordering causing $product->get_type() to still read as simple during woocommerce_process_product_meta).

Changes:

• Derive the effective product type from $_POST['product-type'] (sanitized) during save_custom_product_options, with fallback to $product->get_type().
• Use the derived $product_type for product_types filtering when persisting custom option meta.

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