> How much documentation are you required to give users?

Ideally any diagnostic tools you have developed and schematics, the same things you should have available yourself as the OEM. Legislation like this isn't usually designed to make companies make walkthroughs for replacing a BGA component on a board, but to make resources available so customers can get their products repaired at a 3rd-party repair center for a lower cost (or optionally themselves if they are capable of performing the repair on their own with the documentation made available to them).

> If a device relies on programmable hardware, is it really "repairable" if you don't have the source code? What if there's a security vulnerability in the software, how do you fix that?

Provide pre-programmed IC's, everyone is happy. Requiring the source code for firmware to be available would have huge ramifications for the protection of proprietary IP, and while I would love for companies to release open-source firmware for components I realize forcing them to do so is a straight up no-go.

The goal of repairing a device is to get it back to (or as close as feasible) the state it was originally delivered, anything else is modification.

> If the ICs can be replaced but the original manufacturer stopped selling them, what then?

Not much you can do here, if you as the OEM can't source replacement parts you say "tough luck" and maybe offer a replacement at a reduced cost if you're a nice guy. Unfortunately this does mean 3rd party shops have to turn away work, but such is life, you can can only control companies you source parts from so much.

> Do the electronic interfaces between all the components need to be documented?

Pinouts and the connections between components should be documented ideally, including any voltage and/or resistance on the line so they can be properly inspected with a multimeter. Knowing the electrical communication details between two chips does me no good, knowing it operates at a certain frequency might me useful though to verify with an oscilloscope.

> How do small device manufacturers stay in compliance?

The same way large ones do. Provide documentation for download, buy spare components and offer them for resale at a markup to cover your costs.

> Do end-user repairs void the warranty if the user is just bad at soldering and screwed up a surface-mount part?

Yes, this is already federal law under the Magnuson Moss Warranty Act, manufacturers cannot require they get repairs from certified vendors or even use certified replacement parts - but they can void the warranty if the unauthorized repair caused further damage.

> If the original design of the product was defective in some way, do consumers have the right to fix defects, or only to do repairs that return them to the original condition they were in when delivered to them?

The latter. I mean, as a consumer once you have the device you are free to do whatever the hell you want with the physical object itself - but if you start modifying it beyond the factory state you have no guarantee of support.

Whether this bill implements these is unknown, I can't find the text anymore - but the above answers are reasonable responses to your questions that shouldn't impose more than a minimal burden on businesses.