fix: prevent shared element handoff flashing

[milkevich]

Summary

The source shared element was hidden with visibility: hidden immediately after its clone was inserted, before mobile Safari had painted that clone. At the destination, the real target was also hidden with visibility, then revealed at the exact moment the 64 ms clone fade began. That creates a brief empty frame.

Fix

• Mount the clone nearly transparent first.
• Wait for cloned elements to load.
• Wait two browser paint frames.
• Swap source opacity to 0 and clone opacity to 1 together.
• Use opacity instead of visibility, so elements remain paintable.
• Wait for any incoming visual clone before movement begins.
• Reveal the real target while the portal clone remains fully visible.
• Wait two painted frames before fading the clone.
• Wait another frame before cleanup removes the portal.
• Preserve cancellation and cleanup behavior.

Validation

• npm run check
• npm run build
• Tests cover new or changed behavior
• Public documentation matches verified behavior
• Public API and package contents were reviewed
• Visual styling and layout are unchanged unless required by the change

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
routeveil	Ready	Preview, Comment	Jul 25, 2026 7:12am