Does that really matter? Couldn't you just say "Federal Buildings are in the jurisdiction of the District of Columbia, everything else is in the jurisdiction of Maryland"?
If that doesn't work, it doesn't really matter that much if you sweep up a few commercial buildings into DC. Most of those federal buildings are mixed in with retail, hotels, convention centers, offices, and the like, which doesn't cause disenfranchisement if you include them within DC. The big problem is residential areas.
The district would be subservient to the state for taxes, lease contracts etc. but it's entirely possible to treat the individual buildings as "sovereign territory of the District of Columbia" just like how the little townhouse in London is Ecuadorian territory, and thousands of other embassies around the world like it.
Once you walked off the sidewalk, or off the third floor elevators, or through that door, etc, you would be on "federal turf" so to speak. It's not about a geographical circle.
None of these are particularly new questions. There are federal buildings and federal leased space in every major city across the US. The feds have their own Federal Protective Service Police that respond to incidents on federal property in major cities nation wide. Fire/EMS is usually handled by the locals.
The core national mall area is already protected by US Park Police, it would be possible to create a core DC area as a national park and return the rest of all land to the states. Federal buildings on land returned to the states would be treated like any other federal building in a state. There are plenty of federal buildings in NoVa and Maryland already.
If that doesn't work, it doesn't really matter that much if you sweep up a few commercial buildings into DC. Most of those federal buildings are mixed in with retail, hotels, convention centers, offices, and the like, which doesn't cause disenfranchisement if you include them within DC. The big problem is residential areas.