Shift cable to front DR suddenly very loose
 

On a 21 mile bike ride yesterday, my front DR suddenly stopped working. It was dark so I couldn't tell what happened and kept on riding the remaining 11 miles.

Once I got it home and took a look at it in the light, it was apparent that the shift cable was very slack. I checked it from the brifter to the DR and it appears to be intact and attached at both ends. I pulled on it from either direction and it doesn't seem to be broken.

I can't figure out what happened. Any ideas?

check guide under BB it may be cracked or FD slipped down check bolts.
Look good they crack along the cable line of path so remove and look if needed.

Or the cable slipped through the clamp on the derailleur. It might not have been quite tight enough.

Okay, I will look closer at those things. Thanks!

housing exploded

Also double check that the head hasn't pulled out of the lever by pulling it away from the frame and shifting against hand tension, the cable must move cleanly as you move the lever. If it does, the problem is downstream, most likely a loose FD pinch bolt. (you'll see marks on the wire where it slipped)

slowandsteady, Might be unlikely, but the cable housing may've become reseated.?

Brad