Cannot create a sparse array in runes mode

[Zlendy]

Describe the bug

If the delete keyword is used to remove an item from an array (i.e., create a sparse array) in runes mode, every item following the requested one will be removed as well.

This behavior is different from the one in legacy mode, which I consider to be the correct behavior.

Reproduction

• Runes mode (Buggy): https://svelte.dev/playground/8fb588588e0f48719879970b8a48ecd8?version=5.36.1
• Legacy mode (Works fine): https://svelte.dev/playground/4b629ebddb164a7ebfeeba4800621e00?version=5.36.1

Logs

System Info

System:
    OS: Linux 6.14 Fedora Linux Asahi Remix 42 (Forty Two [Adams])
    CPU: (8) arm64 unknown
    Memory: 2.26 GB / 15.27 GB
    Container: Yes
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.16.0 - /run/user/1000/fnm_multishells/20738_1752596942062/bin/node
    Yarn: 1.22.22 - /run/user/1000/fnm_multishells/20738_1752596942062/bin/yarn
    npm: 11.4.2 - /run/user/1000/fnm_multishells/20738_1752596942062/bin/npm
    pnpm: 10.11.0 - /run/user/1000/fnm_multishells/20738_1752596942062/bin/pnpm

Severity

annoyance

[7nik]

So, it was introduced in #13549: as $inspect is sync, it logs every step of built-in methods, e.g. shift:

init   Array(3) [ 1, 2, 3 ]
update Array(3) [ 2, 2, 3 ]
update Array(3) [ 2, 3, <1 empty slot> ]
update Array(2) [ 2, 3 ]

The 3rd line isn't printed currently.
For a moment, undefined (empty slot) slips into the array and can cause an error if $inspect prints something derived from this array that doesn't expect an undefined value.