Short answers, pulled from the story.
The Convention of Cintra was an agreement signed on the 30th of August 1808, during the Peninsular War. It allowed the defeated French forces under Jean-Andoche Junot to evacuate from Portugal without further conflict, transported by the Royal Navy to Rochefort with all their equipment and personal property.
The convention was signed at the Palace of Queluz, in Queluz, Cintra, in the Estremadura region of Portugal.
Many in Britain viewed the convention as a disgrace because a clear military victory at Vimeiro had been turned into a negotiated French escape. Critics were also angered that a blockaded Russian squadron in Lisbon was allowed to sail to Portsmouth and return to Russia, despite Britain and Russia being at war, a matter Dalrymple had not addressed with the Royal Navy.
All three commanders were cleared by the official inquiry, which was held in the Great Hall at the Royal Hospital Chelsea from the 14th of November to the 27th of December 1808. Wellesley soon returned to active duty in Portugal, while Burrard and Dalrymple were pushed into retirement and never saw active service again.
Some 20,900 French troops were evacuated from Portugal to Rochefort by the Royal Navy, along with all their equipment and personal property. Junot arrived at Rochefort on the 11th of October 1808.
Wordsworth wrote a prose pamphlet titled The Convention of Cintra in 1808 and also composed a sonnet lamenting the bondage of "suffering Spain", even though the convention concerned only Portugal. The sonnet was included in his Sonnets Dedicated to Liberty, and delays in publication caused the pamphlet's journalistic and satirical content to be largely overlooked.