Cable routing through a Shimano ST-6800 dual action leverset to the derailleur.
Similar models are ST-4700, ST-4703, ST-5800, ST-9000, ST-9001 found in the Tiagra, 105, Ultegra and Dura-Ace groupsets.
Symptoms of cable failure are gradual, include chain not changing gears on cassette when shifter is operated, derailleur not moving at all when shifter is operated. Braking is totally unaffected.
Shimano Ultegra dual control lever
https://si.shimano.com/en/pdfs/dm/ST0...
Shifter mounting bolt 6.0 - 8.0 N·m {53 - 71 in. lbs.}
Shifter housing screw 0.20 - 0.25 N·m {1.7 - 2.2 in. lbs.}
Derailleur cable clamp bolt 6 - 7 N·m {53 - 62 in. lbs.}