Not routing the cable under the pinch bolt at the mech,rather than over are you- reducing the leverage?? No, cos he said there was no movement on the cable. . .
Rigth then,
-possible brakage inside the sti
- possible cable stop on the trimble pulled INTO the frame (not good. . )
-The outer wasn't seated peoperly at the lever and has just jumped into its socket
-the ratchet has got caught in the lever- you'll need to release tension to release it.
Either way, i think the cable has to cme out themech so you can evaluate the lever alone, independant of all other components. Job for the evening. .