Thanks Afmob for what I initially thought was a hard puzzle but with hindsight it wasn't.
When I first tried it I got stuck because after step 9 I moved on to other things rather than doing the obvious follow up in step 10. Maybe subconsciously I'd been avoiding listing those combinations.
When I came back to this puzzle I found step 10 easily enough and realised its importance in providing the key killer triples in steps 11 and 14. The only difficult remaining part was step 16 as you will see from the comments in my walkthrough.
I'll rate A158 at 1.25; maybe step 6 could be omitted and then I'd make it Easy 1.25.
Here is my walkthrough
Prelims
a) R1C3 + R2C4 = {15/24}
b) R1C7 + R2C6 = {16/25/34}, no 7,8,9
c) R2C1 + R3C2 = {17/26/35}, no 4,8,9
d) R2C9 + R3C8 = {19/28/37/46}, no 5
e) R67C4 = {49/58/67}, no 1,2,3
f) R67C6 = {29/38/47/56}, no 1
g) R78C5 = {29/38/47/56}, no 1
h) R9C12 = {49/58/67}, no 1,2,3
i) R9C89 = {16/25/34}, no 7,8,9
j) 21(3) cage at R1C2 = {489/579/678}, no 1,2,3
k) 11(3) cage at R1C8 = {128/137/146/236/245}, no 9
l) 22(3) cage in N3 = {589/679}, 9 locked for N3, clean-up: no 1 in 10(2) cage
m) 10(3) cage at R6C1 = {127/136/145/235}, no 8,9
n) 10(3) cage in N7 = {127/136/145/235}, no 8,9
o) 21(3) cage in N9 = {489/579/678}, no 1,2,3
p) 28(4) cage at R7C3 = {4789/5689}, no 1,2,3
1. 45 rule on R123 2 innies R3C19 = 7 = {16/25/34}, no 7,8,9
2. 45 rule on R9 2 innies R9C37 = 12 = {48/57}/[93], no 1,2,6, no 9 in R9C7
3. 45 rule on C1234 2 innies R19C4 = 11 = {29/38/47/56}, no 1
4. 45 rule on C6789 2 innies R19C6 = 11 = {29/38/47/56}, no 1
5. 45 rule on N7 1 outie R8C4 = 1 innie R7C1 + 6, R7C1 = {123}, R8C4 = {789}
6. Hidden killer triple 1,2,3 in R7C1 and 10(3) cage for N7 -> 10(3) cage must contain two of 1,2,3 = {127/136/235} (cannot be {145} which only contains one of 1,2,3), no 4
7. 45 rule on C12 3 innie R145C2 = 1 outie R3C3 + 21
7a. Max R145C2 = 24 -> max R3C3 = 3
7b. Min R3C3 = 1 -> min R145C2 = 22, no 1,2,3,4, 9 locked for C2, clean-up: no 4 in R9C1
7c. 15(3) cage in N1 can only contain one of 1,2,3, R3C3 = {123} -> no 1,2,3 in R1C1 + R2C2
8. 45 rule on C89 1 outie R3C7 = 3 innies R145C8 + 1
8a. Min R145C8 = 6 -> min R3C7 = 7
8b. Max R145C8 = 8, no 6,7,8,9, 1 locked for C8, clean-up: no 6 in R9C9
9. Hidden killer pair 1,2 in R9C456 and R9C89 for R9, R9C456 cannot have both of 1,2 -> R9C89 must contain one of 1,2 -> R9C89 = [25/52/61], no 3,4
10. R9C456 = {139/148/238/247} (cannot be {157/256} which clash with R9C89, cannot be {346} which don’t contain 1 or 2), no 5,6, clean-up: no 5,6 in R1C4 (step 3), no 5,6 in R1C6 (step 4)
10a. 1 of {139} must be in R9C5 -> no 9 in R9C5
11. Killer triple 7,8,9 in R19C4, R67C4 and R8C4, locked for C4
12. 45 rule on N9 1 innie R7C9 = 1 outie R8C6 + 1, no 1 in R7C9, no 9 in R8C6
13. 21(3) cage at R1C2 = {489/579/678}
13a. R3C4 = {456} -> no 4,5,6 in R1C2 + R2C3
14. 15(3) cage in N1 must contain one of 7,8,9 because R3C3 = {123}
14a. Killer triple 7,8,9 in R1C2, R2C3 and 15(3) cage, locked for N1, clean-up: no 1 in 8(2) cage
15. 45 rule on N3 4 innies R1C78 + R2C7 + R3C9 = 13 = {1237/1246/1345}, no 8
[I first saw the next step as
10(3) cage in N7 cannot be {235} because R6C2 = 1 (hidden single in C2) clashes with R7C1 = 1 (hidden single in N7) -> 10(3) cage in N7 (step 6) = {127/136}, no 5, 1 locked for N7, clean-up: no 7 in R8C4 (step 5)
Then I improved it to
1 in C2 locked in R678C2
1 in R6C2 => R8C1 = 1 => 10(3) cage in N7 (step 6) = {127/136}
1 in R78C2 => 10(3) cage in N7 (step 6) = {127/136}
-> 10(3) cage in N7 (step 6) = {127/136}, no 5, 1 locked for N7, clean-up: no 7 in R8C4 (step 5)
The first way ought to have given me the necessary clue. However it was only after I mentioned these two somewhat “chainy” ways to Ed and got his reply “Get the shoe ready for a self-inflicted kick Andrew.
CPE!” that I immediately spotted what I ought to have seen earlier.]
16. 1 in C2 locked in R678C2, CPE no 1 in R7C1, clean-up: no 7 in R8C4 (step 5)
16a. 1 in N7 locked in 10(3) cage (step 6) = {127/136}, no 5
17. 10(3) cage at R6C1 = {127/136/235} (cannot be {145} because R7C1 only contains 2,3), no 4
18. R9C12 = [58/85/94] (cannot be {67} which clashes with 10(3) cage), no 6,7
19. R9C8 = 6 (hidden single in R9), R9C9 = 1, clean-up: no 4 in R2C9, no 5 in R8C6 (step 12), no 9 in R9C46 (step 10), no 2 in R1C4 (step 3), no 2 in R1C6 (step 4), no 6 in R3C1 (step 1)
19a. 21(3) cage in N9 = {489/579}, 9 locked for N9, clean-up: no 8 in R8C6 (step 12)
19b. 2 in R9 locked in R9C456, locked for N8, clean-up: no 9 in R78C5, no 3 in R7C9 (step 12)
20. R8C6 = 1 (hidden single in N8), R7C9 = 2 (step 12), R7C1 = 3, R8C4 = 9 (step 5), clean-up: no 6 in R1C7, no 5 in R3C1 (step 1), no 5 in R3C2, no 8 in R3C8, no 4 in R3C9 (step 1), no 4 in R67C4, no 2,8,9 in R6C6, no 8 in R8C5, no 2 in R9C4 (step 3), no 3 in R9C7 (step 2)
21. R7C2 = 1 (hidden single in R7), R8C12 = 9 = {27}, locked for R8 and N7, clean-up: no 4 in R7C5, no 5 in R9C7 (step 2)
21a. R9C1 = 9 (hidden single in R9), R9C2 = 4, clean-up: no 7 in R1C4 (step 3), no 7 in R1C6 (step 4), no 8 in R9C37 (step 2)
21b. R9C37 = [57], clean-up: no 4 in R1C4 (step 3), no 4 in R1C6 (step 4), no 1 in R2C4
21c. Naked pair {38} in R19C4, locked for C4, clean-up: no 5 in R67C4
21d. Naked pair {67} in R67C4, locked for C4
21e. Naked triple {238} in R9C456, locked for N8, clean-up: no 3 in R6C6
22. R8C7 = 3 (hidden single in R8), R7C7 = 5 (cage sum), clean-up: no 2,4 in R2C6, no 6 in R8C5
23. Naked pair {48} in R8C89, locked for R8 and N9 -> R7C8 = 9, R78C3 = [86], R8C5 = 5, R7C5 = 6, R67C4 = [67], R7C6 = 4, R6C6 = 7
24. R7C1 = 3 -> R6C12 = 7 = {25}, locked for R6 and N4
25. R3C2 = 3 (hidden single in C2), R2C1 = 5, R6C12 = [25], R8C12 = [72], clean-up: no 1 in R1C3, no 2 in R1C7, no 7 in R2C9, no 4 in R3C1, no 5 in R3C9 (both step 1)
25a. R3C19 = [16], R3C3 = 2, R1C3 = 4, R2C4 = 2, R1C7 = 1, R2C6 = 6, R2C7 = 4, R23C8 = [87], R2C9 = 3, R3C7 = 9, R1C89 = [25], R3C6 = 5 (cage sum), R3C45 = [48], R2C23 = [79], R1C12 = [68], R1C456 = [379], R9C4 = 8, R9C6 = 2 (step 4), R9C5 = 3, R8C89 = [48]
25b. R6C8 = 3, R6C9 = 9 (cage sum), R6C3 = 1, R5C4 = 5, R5C2 = 9 (cage sum)
and the rest is naked singles