The Texan leaders meeting at the Constitutional Convention of 1836 primarily led to the drafting of the Texas Declaration of Independence and the establishment of a government for the Republic of Texas. However, in the context of the choices you've provided, the most directly related consequence would be the Mexican government demanding the settlers of Gonzales return their cannon. This event, known as the "Lexington of Texas," occurred in 1835 and was a significant escalation leading up to the Texas Revolution, which ultimately resulted in the broader conflict that the Convention was addressing.
While the other events listed, such as the Goliad Massacre and the retreat of Sam Houston's troops, were significant battles and consequences of the war, they were not direct results of the Constitutional Convention of 1836 itself.