what is this cable? (brake related)

[Tree]

i hadn't ridden my RR6+ in several months due to a shoulder injury, and was getting it back in shape to begin riding, when i noticed a cable related to the front brake handle appears to have somehow been sheered off, or broken, or well, not attached.

it is not one of the main cables bundled together at the top of the brake (picture one), but rather a cable that hooks to the underside (picture two of the REAR brake handle showing what it should look like).

picture 3 is the damage.

the brake appears to be working fine - granted, i only tooled around for a block or two in my neighborhood - so, what is this cable, and is this a fix a semi handy but not terribly handy person could do?

[Ddaybc]

I don't own a RR6+ so I don't know for sure but that "cable" in pic 2 sure looks like it's a hydraulic line for hydraulic brakes.
When you tested it and the brakes worked were you testing just the faulty one or did you, out of habit, use both brakes? I suggest you test it again and use only the faulty one. That may point you in the right direction.

[Tree]

i've since learned from another forum it's the sensor cable - definitely tells the brake light when to go on and off, but may also affect the motor shut off that is part of braking, although i'm thinking it won't be an issue since i'm not likely to brake with my front brake only ever.

[biker bob]

hey guys so i have the rad city 5 i bought second hand on facebook marketplace and i have to replace the rear brake lever and gear changer on same (right side) now i also noticed the same little cable at first had no idea where it went as the brake lever was broken and not attached to bike . so its a sensor you said .  now could i just not use it or do i need to buy an original lever , i do have other levers here but none like the one it came with .thank in advance