You convert an AoH into an H in P::RD the same way you would anywhere else. Convert each hash into a list, combine the lists, and create a hash from the combined list.

    test: expr(s) /^\Z/
        { { map %$_, @{$item{"expr(s)"}} } }
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That's a lot of curlies X_X

Update: Changed map { %$_ } to map %$_, to remove a pair of curlies.