how is my solution not more euclidean-near (to the target square) than the supposed one ?

One possible path:            Your path:                
                                                        
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.▓.▓▓▓▓▓.▓....▓▓▓▓PP▓▓▓..▓    .▓.▓▓▓▓▓.▓....▓▓▓▓P.▓▓▓..▓
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.▓▓.▓.▓▓.▓▓▓P..▓.▓..▓▓▓▓▓.    .▓▓.▓.▓▓.▓▓▓.P.▓.▓..▓▓▓▓▓.
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..▓▓▓▓..▓..▓▓..▓..▓....▓.▓    ..▓▓▓▓..▓..▓▓..▓..▓....▓.▓
▓..▓▓▓.▓▓▓..▓..▓.▓.▓.▓..▓.    ▓..▓▓▓.▓▓▓..▓..▓.▓.▓.▓..▓.
▓▓.▓.▓......▓▓..▓▓.▓.▓▓..▓    ▓▓.▓.▓......▓▓..▓▓.▓.▓▓..▓

Your length: 31.041630560342625

Expected:	30.213203435596434

wtf indeed