Grey cell sum of two digits, need tester

[Thorsby]

EDIT: THIS PUZZLE IS BROKEN

I am looking for a tester for a sudoku puzzle. 4 star difficulty?

Rules: Normal sudoku rules apply.

A digit in a grey cell is part of a string of 3 digits in a straight line, going either horizontally or vertically. (Not diagonally.) The digit in the grey cell is always at the start or end of the string, never in the middle. The digit in the grey cell is the sum of the other two digits in the string.

All possible grey cells are given.

Example:


The puzzle:

Solve in penpa.

[Dandelo]

I have solved it (45 min + ca 15 min), but at some points I've made 'obvious' steps without proving them. My feeling is: "It is uniquely solvable!" But I wouldn't guarantee this.

[Dandelo]

BTW, interesting rule set, nice puzzle. In fact it was not easy, but after understanding the rules and their consequences it is easier than 4 stars IMO.

[Thorsby]

Thank you. I would like to have to have the steps proven though, so I'm still looking for a tester.

[colski]

Thank you. I would like to have to have the steps proven though, so I'm still looking for a tester.

I did this puzzle. some numbers don't go in grey squares. reduce box 1 to symmetric choices of 2 candidates. find where to place 4 and 6 in box 7. proceed until only 3 grey cells remain. I still have two candidates in 2 places of column 4 and 5 places of column 6. the three grey cells in boxes 3,6,9 have 4,2,4 combinations but only one of those seems to work. I don't see a way to resolve that other than trial and error, though.