OK, so I had booked this itinerary:

Flight information

Sat, Apr 11, 2009 - BOS to DME
United 0823
Depart: BOS 14:31
Arrive: IAD 16:11 Non-stop
1h 40m
733
413 miles traveled Fare basis code:
TLWAXZ87
Booking class: NF
First
413 Award miles
No Meal Service
Flight: Confirmed
Upgrade: Confirmed
Seats:01D
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<<< connecting to >>>
United 0964
Operated by:
Depart: IAD 16:50
Arrive: DME 10:45
Arrives next day
Apr 12 Non-stop
9h 55m
763
4,907 miles traveled Fare basis code:
TLWAXZ87
Booking class: T
Economy
4,907 Award miles
Dinner, Snack
Flight: Confirmed
Seats:20C
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Sun, Apr 12, 2009 - DME to IAD
United 0965
Depart: DME 12:35
Arrive: IAD 15:30 Non-stop
10h 55m
763
4,907 miles traveled Fare basis code:
TLWAXZ87
Booking class: T
Economy
4,907 Award miles
Lunch, Snack
Flight: Confirmed
Seats:20C
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Sun, Apr 12, 2009 - IAD to BOS
United 0898
Depart: IAD 22:00
Arrive: BOS 23:32 Non-stop
1h 32m
752
413 miles traveled Fare basis code:
TLWAXZ87
Booking class: NF
First
413 Award miles
No Meal Service
Flight: Confirmed
Upgrade: Confirmed
Seats:03D
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PenaltyNON-REFUNDABLE APEX FARE

...for the princely sum of about 454 USD. As you can see, it's a same day turnaround flight, so I should have been clear with out the visa (per the TWOV rules).

The astute readers will notice the time... supposedly I'd be on that flight now. Sadly, the front agent in BOS refused to issue me boarding passes for any part of this flight. Now what do I do?