cs6 - There Must Be A Way: Trimming Groups Of Lines To Fit Complex Shape - Illustrator

This doesn't seem complex, and I'm not a beginner but can't figure it out or find answer online.

I want to be able to trim a series of lines to fit in a complex shape (lay the shape over a group of stroked paths and trim them so only segments that are within the shape remain). I want actual truncated line segments left so that I can apply strokes, widths, profiles and brushes to what's left.

I understand clipping masks (but they don't leave new endpoints for width/brushes) and envelopes (which bend/distort lines to fit) and have tried all of the pathfinder options with no luck. I can of course just use scissors and cut-cut-cut at each intersecting point, but this isn't a one-off shape it's a process that I want to be able to repeat often across several works.

Essentially it should just be a clipping mask that cuts/deletes line segments outside it and leaves actual line segments (not shapes) behind...seems simple and an obvious function, but I'm stumped. (I'm in CS6)

Thanks for any help!