Slot field named with a key existing within metadata object or somewhere else crashes DnD with arr.some is not a function

[jderboven]

Description

Using Puck, defining a slot field with a name that might exist in other object (such as metadata) causes drag‑and‑drop to crash. Renaming the field to breadcrumbSlot fixes the issue immediately.
Environment

• Package: @puckeditor/core
• Version: ^0.21.x
• Framework: React
• Usage: custom editor with slot fields

Steps to Reproduce

1. Define a component with a slot field named breadcrumb.

 fields: {
   breadcrumb: { type: 'slot' }
 },
 defaultProps: {
   breadcrumb: []
 }

2. Insert the component in the editor.
3. Drag it (or perform a DnD operation).

Expected

• Drag‑and‑drop should work normally.
  Actual
• Crash with:
  TypeError: arr.some is not a function
  at containsPromise
  at walkField
  at walkObject

Notes

• Raw data and defaultProps contain arrays as expected.
• The non‑array value appears only inside the DnD pipeline, before render.
• Renaming breadcrumb → breadcrumbSlot fixes the crash.
• Suggests a collision with an internal field or reserved name.

Proposed Fix

• Add a defensive guard in mapFields / containsPromise for slot values:
  • If a slot value is not an array, treat it as [] or log a warning.
• Alternatively, document breadcrumb (and other internal names) as reserved.
• Better: namespace internal metadata to avoid collisions.

[FedericoBonel]

Hey @jderboven!

Thanks for reporting this, I can indeed reproduce it with the following config.
It seems that, for whatever reason, Puck is mapping the slot value with that name to the metadata property with the same name, and that then, triggers this bug from this line.

Though I think is not an issue of checking the line value, but rather why is it currently merging these values.

const config = {
  components: {
    ContainerExample: {
      fields: {
        breadcrumb: {
          type: "slot",
        },
      },
      defaultProps: {
        breadcrumb: [],
      },
      render: ({ breadcrumb: BreadCrumb, puck }) => {
        console.log(BreadCrumb, puck.metadata);

        return <BreadCrumb />;
      },
    },
  },
};

<Puck config={config} metadata={{ breadcrumbs: "some example" }}>