A plan to open up BART stations to everything from Dunkin’ Donuts to Ghirardelli Chocolate outlets has gone off the rails, with the firm that was behind the idea now suing the transit agency for alleged breach of contract and claiming tens of millions in damages.

“The lawsuit clearly demonstrates that BART was an unreliable partner and did not participate in good faith, nor did it make its internal decisions in a timely manner,” said Evette Davis, spokeswoman for TransMart, the company that promised to attract a range of franchise outlets for BART’s 43 stations.

BART has a different view: “Our position is that TransMart failed to comply with its contractual obligations,” said agency spokesman Jim Allison.

It all started back in 2008 when BART received an unsolicited bid from San Francisco housing developer Alexis Wong, whose political connections had landed her appointments to various state boards and commissions over the years. She told BART she could fill the stations with businesses, creating boatloads of cash for the agency.

TransMart, the company Wong formed to undertake the effort, landed the deal on an 8-1 vote of the BART Board of Directors in 2011. Three years later, about the only thing the firm had to show for its efforts were a couple of pop-up Blinq stores at the Embarcadero and Montgomery stations. The stores — aimed mostly at promoting Wong’s online business, selling everything from clothing to electronics — have since closed.

BART eventually let TransMart’s contract expire, saying the firm had failed to meet a deadline to deliver at least nine retail stores to stations by August 2016.

“It was in everyone’s best interest, we felt, to end the relationship,” Allison said.

Now TransMart has sued in Alameda County Superior Court, claiming BART failed to act in good faith on a deal that Wong’s lawyers say was worth as much as $95 million to the company.

The suit alleges that BART held up the firm’s store designs, “drastically cut” the amount of space it was promised and acted “inappropriately” in rejecting TransMart’s financial plans.

“These guys dragged their feet,” Darius Ogloza, an attorney for TransMart, told us. “Or alternatively, they lost interest and just decided to kill this thing.”

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or email matierandross@ sfchronicle.com. Twitter: @matierandross