FYI, #4 "Empty an array" will create a holey array. It's better to assign the value a new empty array  rather than mutate the length. More on element kinds: v8.dev/blog/elements-kinds
Why would setting the length of an array to 0 make it holey? I would understand if you were to set the length to a value greater than its content, it would create a HOLEY_ELEMENTS. Truncating should not have that same problem.
I would think the engine would continue to optimize for a PACKED_ELEMENTS Array if length were set to a value less than its current content, including 0.
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