Editor V2: Prototype validation display strategy (indicator + drilldown)

[shopify-river]

Summary

Prototype and finalize the validation display strategy for editor V2. Options under consideration:

• Separate floating window
• Pinned element inside the properties panel
• Simple error-count indicator that surfaces the full list on click

Rationale

From the Apr 21 CSOM sync: this was flagged as needs further discussion. Key concern: when there are many validation errors (common mid-edit), rendering the full list inline clutters the UI and users end up dismissing/ignoring it. An indicator-with-drilldown pattern is the preferred starting point.

Acceptance

• Prototype at least the "indicator + drilldown" option.
• Validate against a high-error state (e.g. 20+ errors) to confirm it doesn't clutter the UI.
• Pick a final pattern and apply it consistently across editor V2.

Notes

Separate PR is fine here — decision will be easier once we can see and feel each option.

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Context: Captured from the Tangle / CSOM UX sync on Apr 21, 2026 (notes). Attendees: Matt Beaulne, Camiel van Schoonhoven, Maksym Yezhov.

Requested by Matt Beaulne matt.beaulne@shopify.com.