🎉 This issue has been resolved in version 9.0.11 🎉

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Do I understand this prevents immer from creating sparse arrays with delete? I've spent the evening slowly removing pieces of my stack and API calls trying to find issues with sparse indices. I have no trouble creating sparse arrays using "proxied mutation"

// produces [<empty>,42]
(draftState: Draft<{ values: [] }>) => {
  values[1] = 42;
}

Then:

// produces [undefined, undefined]
// expected [<empty>, <empty>]
(draftState: Draft<{ values: [] }>) => {
  delete values[1];
}

Be careful using the stackblitz console to test the reproduction results. It runs a parser on the input data which casts holes to undefined. Opening the browser's devtools reveals the proper output (no undefined values).