Persistent iframe shape

An iframe shape whose content survives unmounting the editor.

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Shape content normally lives inside the editor's React tree, so unmounting the editor destroys it — an embedded iframe loses its scroll position, in-app state, and connections. This example uses getAppOwnedElement and onReleaseAppOwnedElement to keep an app-owned iframe alive across editor sessions: tldraw adopts the element into the shape with Node.moveBefore (which preserves iframe state, in Chromium 133+ and Firefox 144+) and hands it back to the app before the editor unmounts. Interact with the iframe, unmount the editor, then mount it again — the iframe keeps its state.