Add typed JSON output to theme metafields pull

[gonzaloriestra]

WHY are these changes introduced?

theme metafields pull writes definitions to a file but has no typed, discoverable JSON result.

Closes shop/issues-develop#23694 together with the preceding package and init PRs.

WHAT is this pull request doing?

Use one supported-owner mapping for download requests, required definition keys, and the failed-owner enum. Adding a supported owner updates the output schema together with the downloader.

Return downloaded definitions and the output path as typed data, with explicit failed and skipped outcomes. Preserve the file contents, text messages, partial downloads, nonfatal total-fetch failures, and silent downloads used by theme dev. JSON results go to stdout; diagnostics stay on stderr.

Normal output:

Metafield definitions have been successfully downloaded.

Matching JSON example:

{
  "status": "downloaded",
  "path": "/themes/example/.shopify/metafields.json",
  "definitions": {
    "article": [],
    "blog": [],
    "collection": [],
    "company": [],
    "company_location": [],
    "location": [],
    "market": [],
    "order": [],
    "page": [],
    "product": [
      {
        "key": "subtitle",
        "namespace": "custom",
        "name": "Subtitle",
        "description": null,
        "type": {
          "name": "single_line_text_field",
          "category": "TEXT"
        }
      }
    ],
    "variant": [],
    "shop": []
  },
  "failedOwnerTypes": []
}

How to manually test your changes?

pnpm i -g --@shopify:registry=https://registry.npmjs.org @shopify/cli@0.0.0-snapshot-20260928103209
shopify theme metafields pull --store YOUR_STORE --path YOUR_THEME
shopify theme metafields pull --store YOUR_STORE --path YOUR_THEME --json
shopify theme metafields pull --json-schema

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• A single changeset for all theme migrations is added in the last PR, #8682.

[isaacroldan]

Do we know if this is a stable list of fields or if it can easily change? if it changes often this can get stale soon

[gonzaloriestra]

The list was actually copied from metafields-pull.ts. I removed the duplicated lists: all share the handleToOwnerType mapping defined here now.

[github-actions]

Differences in type declarations

We detected differences in the type declarations generated by Typescript for this branch compared to the baseline ('main' branch). Please, review them to ensure they are backward-compatible. Here are some important things to keep in mind:

• Some seemingly private modules might be re-exported through public modules.
• If the branch is behind main you might see odd diffs, rebase main into this branch.

New type declarations

We found no new type declarations in this PR

Existing type declarations

packages/cli-kit/dist/public/node/base-command.d.ts

@@ -35,6 +35,7 @@ declare abstract class BaseCommand extends Command {
         argv: string[];
     }>;
     protected environmentsFilename(): string | undefined;
+    protected validateNonTTYFlags(flags: FlagOutput): void;
     protected failMissingNonTTYFlags(flags: FlagOutput, requiredFlags: string[]): void;
     private failMissingNonTTYFlagRequirements;
     private applicableNonTTYFlagRequirements;