I'd like Timo to weigh in. I wonder if 31 could have sneaked in
Back from the holidays...
So, my take:
1) Odo reaches Alpha.
2) The Dominion learns of Alpha, inserts all sorts of agents, starts planning a takeover plus recovery of Odo.
3) The Federation learns of the Dominion. S31 starts planning a bioweapon to preempt or win the upcoming war.
4) "Adversary": Odo ruins his chances of getting peacefully readopted.
5) "Homefront": S31 injects Odo with a bioweapon that will kill slowly all Founders, including Odo. Hopes for the Founders to again try and get Odo.
6) "Broken Link": the Founders oblige, triggering their own thing in Odo, inserted by their agent in red Chalan. It's not deadly and is not related to the bioweapon in any fashion. Odo infects the Link and the Founders start dying. But the Founders Solidify Odo, who thus is cured - or at least has the weapon effect put on hold.
7) "The Begotten": the Founders decide Odo has served his sentence and bribe Quark to give Odo the Changeling baby basically for free. The baby lifts the Solidity sentence and, having served its task, dies. Odo possibly again starts advancing towards his inevitable death from the bioweapon.
8) "Behind the Lines": if Odo wasn't re-infected already, he now is.
9) "Extreme Measures": the cure is uncovered and Odo healed.
10) "What You Leave Behind": Odo brings the cure to the Link, which promptly judges him for his treason and executes him.
It's too much to expect that Odo's collapse in "Broken Link" could have been coincidence, which it would need to be if this were related to the S31 bioweapon... A re-infection around "Behind the Lines" works fine in terms of progression of symptoms, but so does re-onset of effects in "The Begotten", give or take.
Timo Saloniemi