[gonzaloriestra]

WHY are these changes introduced?

Fixes https://github.com/shop/issues-develop/issues/24321.

Agents need structured live output from hydrogen dev. This builds on the Dev Instance layer, following Shopify/cli#8996.

WHAT is this pull request doing?

Add --json (-j, SHOPIFY_FLAG_JSON) to stream the same JSONL bytes to stdout and the session log. Reuse CLI Kit's typed log schema for readiness, runtime messages, requests, file changes, codegen output, recoverable errors, and shutdown. CLI diagnostics use stderr; fatal errors use the standard JSON error envelope on stdout. There is no final success result.

Run codegen watchers from the storefront directory so relative schema and document paths work with --path, while preserving explicit config paths.

Keep --no-input independent. Disable terminal shortcuts and banners in JSON mode, keep existing noise filters without debouncing repeated worker messages, capture console methods including dir and table, and expose schemas through --json-schema. Update command help and the manifest, and remove dev's typed JSON lint exception.

Declare the command schema as a static field. Patch the pinned CLI ESLint rule to accept initialized schema fields, matching the rule in Shopify/cli.

How to manually test your changes?

1. Using this checkout's linked CLI and an existing project, run pnpm shopify hydrogen dev --path /path/to/project --json --no-input > /tmp/hydrogen-dev.jsonl with existing authentication and configuration.
2. Read readiness URLs from the stream or instance JSON. Change a route and request a page with a query string. Check that each stdout line parses as JSON and requests retain the query string.
3. Add a temporary worker console.log or console.table, and trigger a recoverable worker error. Confirm messages reach the stream while the session continues.
4. Press Ctrl+C once and compare /tmp/hydrogen-dev.jsonl with the session's retained logFile; their bytes should match.
5. Run pnpm shopify hydrogen dev --json-schema to inspect the record, error, event, and runtime-details schemas.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or functional changes
• I've added tests to cover my changes
• I've added or updated the documentation

[shopify]

Oxygen deployed a preview of your gonzalo/hydrogen-dev-json branch. Details:

Storefront	Status	Preview link	Deployment details	Last update (UTC)
Skeleton (skeleton.hydrogen.shop)	✅ Successful (Logs)	Preview deployment	Inspect deployment	October 28, 2026 4:54 PM

Learn more about Hydrogen's GitHub integration.

[fredericoo]

thank uuu
left a few blocking comments, pls resolve when u can