Prelims
a) 23(3) cage at R3C2 = {689}
b) 7(3) cage at R3C8 = {124}
c) 9(3) cage at R6C1 = {126/135/234}, no 7,8,9
d) 19(3) cage at R8C3 = {289/379/469/478/568}, no 1
e) 8(3) cage at R8C6 = {125/134}
f) 17(5) cage at R1C1 = {12347/12356}, no 8,9
g) 17(5) cage at R1C7 = {12347/12356}, no 8,9
h) 18(5) cage at R7C1 = {12348/12357/12456}, no 9
i) 17(5) cage at R7C7 = {12347/12356}, no 8,9
1. 17(5) cage at R1C7 contains 1,2,3, locked for N3
1a. R3C8 = 4
1b. Naked pair {12} in R4C89, locked for R4 and N4
1c. 17(5) cage at R1C7 = {12356} (only remaining combination), locked for N3
Other steps resulting from Prelims
2a. 17(5) cage at R1C1 = {12347/12356}, 1,2,3 locked for N1
2b. 18(5) cage at R7C1 = {12348/12357/12456}, 1,2 locked for N7
2c. 17(5) cage at R7C7 = {12347/12356}, 1,2,3 locked for N9
2d. Naked triple {689} in 23(3) cage at R3C2, CPE no 6,8,9 in R56C2
3. 8(3) cage at R8C6 = {125/134} -> R89C6 = {12/13}, 1 locked for C6 and N8
3a. Killer pair 4,5 in R8C7 and 17(5) cage at R7C7, locked for N9
4. 8,9 on D\ only in R4C4 + R5C5 + R6C6, locked for N5
4a. R5C5 = 9 (hidden single on D/)
4b. 8 on D/ only in R7C3 + R8C2 + R9C1 -> 18(5) cage at R7C1 = {12348}, locked for N7, no 8 in R7C1 + R9C3
4c. 7 on D/ only in R4C6 + R6C4, locked for N5
5. R7C2 = {56} -> 9(3) cage at R6C1 = {126/135}, R6C12 = {12/13}, 1 locked for R6 and N7
5a. R5C4 = 1 (hidden single in N5)
6. 14(3) cage at R1C6 = {248/257/347} (cannot be {239} which clashes with 8(3) cage at R8C7, cannot be {356} because R2C7 only contains 7,8,9), no 6,9
6a. R2C7 = {78} -> no 7,8 in R12C6
6b. Killer pair 2,3 in 14(3) cage and 8(3) cage, locked for C6
6c. 2 in N5 only in R6C45, locked for R6
7. 12(3) cage at R1C4 = {246/345} (cannot be {237} which clashes with 14(3) cage at R1C6), no 7,8,9
7a. 12(3) cage = {246/345}, CPE no 4 in R2C56
7b. Killer pair 2,3 in 12(3) cage and 14(3) cage, locked for N2
7c. 9 in N2 only in R3C46, locked for R3
7d. 23(3) cage at R3C2 = {689}, 9 locked for R4 and N4
8. R8C3 = 9 (hidden single in C3) -> R89C4 = 10 = {28/37/46}, no 5
8a. R9C8 = 9 (hidden single in R9)
8b. R1C2 = 9 (hidden single in R1)
8c. R2C9 = 9 (hidden single in R2)
8d. Naked pair {68} in R34C2, locked for C2 and 23(3) cage -> R4C1 = 9
8e. R7C2 = 5 -> R6C12 = 4 = {13}, locked for R6 and N4
8f. R9C2 = 7, R8C1 = 6, clean-up: no 3 in R8C4, no 4 in R9C4
8g. 5 in N8 only in R89C5, locked for C5
8h. 3 in N5 only in R4C45, locked for R4
9. 17(3) cage at R6C8 = {458/467} -> R6C9 = 4, R67C8 = [58/67/76]
9a. Killer pair 7,8 in R1C8 and R67C8, locked for C8
9b. R6C7 = 9 (hidden single in N6)
10. Consider placements for 8 in C8
R1C8 = 8 => R2C7 = 7
or R7C8 = 8 => R8C9 = 7
-> no 7 in R7C7
[Cracked. The rest is fairly straightforward.]
11. 7 on D\ only in R1C1 + R3C1 -> 17(5) cage at R1C1 = {12347}, 4,7 locked for N1, no 7 in R1C3 + R3C1
11a. 12(3) cage at R1C4 (step 7a) = {246/345}
11b. R2C3 = {56} -> no 5,6 in R12C4
12. Naked quad {2345} in R12C46, locked for N2
12a. 5 in N1 only in R2C13, locked for R2
12b. R1C6 = 5 (hidden single in N2) -> R2C67 = 9 = [27], R1C8 = 8, R8C9 = 8 (hidden single in N9)
12c. Naked pair {34} in R12C4, locked for C4 -> R89C4 (step 8) = [28]
12d. R12C4 = {34} -> R2C3 = 5 (cage sum), R2C1 = 8, R34C2 = [68]
12e. R89C6 = {13} -> R8C7 = 4 (cage sum)
12f. 17(5) cage at R7C7 = {12356}, locked for N9
12g. R7C8 = 7 -> R6C8 = 6 (cage sum), R4C7 = 5, R5C8 = 3, R2C8 = 1, placed for D/, R8C2 = 3, placed for D/
and the rest is naked singles, without using the diagonals.