I think what I want is: Don't autovivify unless I'm actually performing an assignment or explicitly casting to a hash/array:

$x[2]{z} = 1;   # autovivify $x[2] as a hash
$x[2]{z};       # don't autovivify $x[2]
%{$x[2]};       # autovivify $x[2] as a hash
func($x[2]{z}); # don't autovivify $x[2]
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