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Description

There are several places where library blocks make assumptions that certain Block values are BlockSvg instances.

In some cases these assumptions might be justified—for example, block types that are intended to be used only in mutators will normally be BlockSvg instances—but is risky and prevents those blocks from being safely instantiated in headless mode.

In blocks/lists.ts

• lists_create_with:
  • init method calls new Mutator(/*...*/, this).
  • decompose method calls workspace.newBlock('lists_create_with_container').initSvg() and workspace.newBlock('lists_create_with_item').initSvg().

Reproduction steps

These are theoretical / type safety issues; I have not verified if it's actually possible to cause a crash.

Additional Info

Part of #6920.