I understand that you need a deflector shield to clear a path in front of your starship when travelling at relativistic speeds, such as under impulse drive.
However, since the idea of warp drive is that you create a warp bubble around your ship and compress the space in front of you while expanding it behind you (basically moving the bubble of space that you're sitting in through space) then why do you need a deflector shield? You're not moving relative to the space you're occupying.
Any particle in your path would just get pushed out of the way temporarily as you pass by. That particle wouldn't even move relative to the space it's occupying... the space it's occupying would just get warped.
Now I can't imagine it's good for matter to exist in a highly warped area of space. I imagine any macroscopic bit of matter entering a highly curved area of space would have a lot of internal stresses and absorb a lot of heat, perhaps becoming plasma, so perhaps the deflector shield actually deflects particles out of the path of the warp bubble itself. That energy has to come from somewhere, which has to be the warp drive itself. If it didn't take energy to warp through matter then you could theoretically warp right through a planet or a star without worrying about it, but that's clearly not possible.
Are there any canon explanations for why a deflector shield is needed at warp?