Where? The 1836 document does not reference any earlier agreement, nor does it give the restrictions that you claim were in place in 1805.
I stated I lost my hard drive, and this information. Don't worry though, I found it once and will find it again [the 1836 cession].
The state of South Carolina in their 1805 cession:
That, if the United States shall not, within three years from the passing of this act, and notification thereof by the Governor of this State to the Executive of the United States, repair the fortifications now existing thereon or build such other forts or fortifications as may be deemed most expedient by the Executive of the United States on the same, and keep a garrison or garrisons therein; in such case this grant or cession shall be void and of no effect.Davis documented this, and similar stipulations in various cession agreements by Massachusetts, New York, and Virginia on pages 179-180 of his Rise And Fall of The Confederate Government