Fix React 19 Activity component support: preserve view state across hide/show cycles

[Copilot]

React 19's <Activity> component preserves React state but runs effect cleanup/re-setup on hide/show, causing DeckGL to destroy and recreate its Deck instance — resetting initialViewState and losing user pan/zoom.

Change List

• Save view state on cleanup: before finalize(), snapshot deck.viewState (the internally-tracked uncontrolled view state) into a savedViewState field on the persistent thisRef
• Restore on re-init: if savedViewState is set when the effect re-runs, pass it as initialViewState to the new Deck instance, then clear it
• Controlled mode unaffected: deck.viewState is null in controlled (props.viewState) mode, so the truthy check correctly skips restoration

// cleanup
thisRef.savedViewState = thisRef.deck.viewState; // null in controlled mode
thisRef.deck.finalize();

// setup
if (thisRef.savedViewState) {
  initProps.initialViewState = thisRef.savedViewState;
  thisRef.savedViewState = undefined;
}
thisRef.deck = createDeckInstance(thisRef, DeckClass, initProps);

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Bug] React 19 Activity component support</issue_title>
<issue_description>### Description

Summary

deck.gl's React component doesn't properly support React 19's <Activity> component. When a <DeckGL> component is hidden via Activity and then shown again, the view state resets to initialViewState, losing any user interactions (pan/zoom).

Background

React 19.2 introduced the <Activity> component which hides components without unmounting them. However, Activity has a specific behavior: effect cleanup functions run when hidden, and effects re-run when visible again (while React state is preserved).

Related

• Discussion: Uncontrolled Deck with new React Activity component #9921
• React Activity docs: https://react.dev/reference/react/Activity

Flavors

• Script tag
• React
• Python/Jupyter notebook
• MapboxOverlay
• GoogleMapsOverlay
• CARTO
• ArcGIS

Expected Behavior

Deck should retain state in the hidden activity mode.

Steps to Reproduce

https://github.com/mohadib/deck-activity

This example has 2 maps and a div you can toggle between. One map uses an Activity, and the other uses css display: none when hidden. The css hiding retains state, the activity does not.

Root Cause

The DeckGL component's initialization effect (modules/react/src/deckgl.ts:189-199):

useEffect(() => {
  thisRef.deck = createDeckInstance(thisRef, DeckClass, {...});
  return () => thisRef.deck?.finalize();
}, []);

When Activity hides the component:

1. Cleanup runs → finalize() destroys the Deck instance and its internal view state
2. When shown again → A new Deck instance is created with the original initialViewState
3. User's pan/zoom changes are lost

Environment

• Framework version: 9.2
• Browser: Chrome
• OS: MacOS

Logs

No response</issue_description>

<agent_instructions>i bet you cant one shot this.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes [Bug] React 19 Activity component support #9983

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[charlieforward9]

I imagine there is a cleaner way to do this in a future version that permanently changes the functionality but for now this would be backwards compatible

@mohadib

[chrisgervang]

I was wondering if the issue is isolated to viewState or if other props were resetting as well?

[charlieforward9]

I havent messed with the Activity API yet - @mohadib can you isolate the issue?

[coveralls]

coverage: 91.053% (-0.003%) from 91.056%
when pulling 623e905 on copilot/fix-react-19-activity-support
into 9b4f613 on master.