fix: coordinate mount of snippets with await expressions

[Rich-Harris]

right now stuff sometimes gets mounted at the wrong time. this fixes it

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🦋 Changeset detected

Latest commit: 0b47787

The changes in this PR will be included in the next version bump.

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[Rich-Harris]

uhh whoops i merged in the wrong direction somehow? little confused tbh

[Rich-Harris]

looks like some tests are failing, gonna undo