Add typed JSON output to theme preview

[gonzaloriestra]

Original PR and review history: #8645.

WHY are these changes introduced?

Fixes https://github.com/shop/issues-develop/issues/23695

Preview JSON should expose a stable resource and wait for browser diagnostics.

WHAT is this pull request doing?

Return a strict preview resource with an opaque string ID and validated URL. Keep the native service compatibility adapter, await browser warnings before final output, and retain explicit environment batches. Validate required inputs before authentication and preserve successful results when another environment fails.

The public output follows docs/cli/json-output.md; explicitly named environments use one {environments: [...]} object.

How to manually test your changes?

shopify theme preview --store example.myshopify.com --theme 123 --overrides ./overrides.json --json
shopify theme preview --json-schema

To test a batch, configure staging and production in shopify.theme.toml with store, password, theme, and overrides, then run shopify theme preview --json -e staging -e production.

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
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

[isaacroldan]

There is a regression in the single-environment store fallback.

---

🤖 Generated by the review-pr skill

[isaacroldan]

a small comment

[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/themes/theme-manager.d.ts

@@ -11,5 +11,12 @@ export declare abstract class ThemeManager {
     findOrCreate(name?: string, role?: Role): Promise<Theme>;
     fetch(name?: string, role?: Role): Promise<Theme | undefined>;
     generateThemeName(context: string): string;
-    create(themeRole?: Role, themeName?: string): Promise<Theme>;
+    create(themeRole?: Role, themeName?: string): Promise<{
+        createdAtRuntime: boolean;
+        id: number;
+        name: string;
+        processing: boolean;
+        role: string;
+        src?: string;
+    }>;
 }
\ No newline at end of file

[github-actions]

⚠️ Potential Breaking Changes Detected

This PR contains changes that may break the existing contract.

@shopify/dev_experience — this PR contains breaking changes that require coordination for the next major release.

📦 Major Version Changesets

The following changesets request a major version bump:

Changeset	Package
theme-preview-json-contract.md	'@shopify/cli': major

[karreiro]

Thank you, @gonzaloriestra!