layerStack Duplicate Entry — Minimal Reproduction

Bug

When a Dialog from @ark-ui/react is rendered with open={true} on mount (i.e., not opened via user interaction), the dialog content element gets incorrect data-has-nested="dialog" and data-nested attributes in React Strict Mode — as if a nested dialog were open, even though only a single dialog exists in the DOM.

This results in:

• --layer-index: 1 instead of 0
• data-has-nested="dialog" set on the only dialog
• --nested-layer-count: 1 instead of 0

In production mode (Strict Mode disabled), the bug does not occur. It seems like layerStack ends up with two entries for the same DOM node, likely caused by React Strict Mode's double-invocation of effects where the cleanup doesn't fully undo the first layerStack.add() call.

Steps to Reproduce

npm install
npm run dev

1. Open http://localhost:5173
2. Click "Mount always-open dialog"
3. Inspect the [data-scope="dialog"][data-part="content"] element in DevTools
4. Observe: data-has-nested="dialog", --layer-index: 1, --nested-layer-count: 1
5. The in-app inspector confirms the bug

Expected Behavior

A single open dialog should have:

• --layer-index: 0
• --nested-layer-count: 0
• No data-has-nested attribute

Versions

• @ark-ui/react: 5.36.0
• @zag-js/dismissable: 1.39.1
• @zag-js/react: 1.39.1
• react: 19.x (Strict Mode enabled)
• vite: 6.x