Add deprecation warning to renderMode

[james-a-c]

Background

Closes https://github.com/shop/issues-checkout/issues/11640
vault decision

Following the introduction of split ship and pickup the purchase.checkout.pickup-location-option-item.render-after target is now shared between rendering inline and in a modal. The decision was made to not support modal within modal functionality and to not encourage third party developers to build solutions which utilize this. To be consistent across checkout this thinking should hold true for other targets that render both inline and in a modal:
purchase.checkout.shipping-option-item.render-after
purchase.checkout.shipping-option-item.details.render

renderMode should be deprecated today and the blocking of modal within modal functionality will occur in the future once the renderMode has been removed

Solution

Add a deprecation warning for renderMode on ShippingOptionItem

Checklist

• I have 🎩'd these changes
• I have updated relevant documentation

[james-a-c]

• Add deprecation warning to renderMode  #4509 👈 (View in Graphite)
• 2026-07-rc

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[lucasmedeirosleite]

LGTM!

[jamesvidler]

I don't like that we are deprecating this, and not providing any alternative for rendering a modal.

We are actively trying to encourage folks to migrate to newer API versions to adopt remote-dom (and its performance improvements), and we should not introduce additional footguns, especially if it requires them to change how their extension works.

If the plan is to have different extension targets to support this, then that should be added in the same API version so there is a clear migration path.

These changes should also be introduced to the private checkout-web package (in world) prior to the release candidate.

[reykjalin]

Looks good to me 👍

[jamesvidler]

Approving to unlock this PR. We are aligned in the intention to remove the concern of renderMode for UI extensions those targets.