Vladimir Putin is a master manipulator. In turn, any diplomatic arrangement he agrees to which appears to weaken his interests should be scrutinized. He is up to something.
That's exactly the case in relation to Monday's presidential agreement between Recep Tayyip Erdogan of Turkey and Vladimir Putin of Russia. Meeting in Sochi, the leaders announced a deal to stave off an imminent Syrian-Russian-Iranian axis offensive on Syria's Idlib province. That province is controlled by a mix of Syrian Islamic-nationalist rebels and Salafi-Jihadist groups. But Erdogan rightly fears the offensive might kill hundreds of thousands of civilians and wants to prevent it.
But this deal won't achieve that objective, at best it will delay the offensive for a few weeks. Because this isn't a peace deal, it's a Putin fiction to manipulate Erdogan into accepting the very offensive he opposes.
As reported by Kremlin state media outlet RT, the agreement involves Russia and Turkey establishing a "15-20 kilometer" wide demilitarized zone under joint Turkish-Russian military monitoring. But while Putin suggests this will counter terrorist groups while protecting others, reality suggests otherwise. Most obviously, Putin draws no distinction between Islamist-nationalist rebels and Salafi-Jihadist terrorist groups in Idlib. Nor, as his frequent airstrikes on previously identified hospitals prove, does the Russian leader draw much distinction between civilians and rebels. Putin only cares about his ultimate objective: Bashar Assad's unhindered control over Syria. And this demilitarized zone will do very little to nothing towards achieving Putin's objective.
Yet the real absurdity here is the distinction in how the two leaders describe the deal's details. Erdogan claims that the deal means that the "Syrian opposition that is holding these territories will remain there. But together with Russia, we will make efforts to clear these territories of radical elements."
Meanwhile, Putin asserts that "Before the end of the year, roads between Aleppo and Hama, and Aleppo and Latakia must be reopened for transit traffic."
But those two statements cannot co-exist in reality. As my annotated map below shows, the roads that Putin is describing here are the main arterial highways from northern Idlib all the way south into Assad-controlled territory.

The idea that those roads will be open and thus controlled by Syrian regime traffic (which is what Putin means by "transit traffic"), and also under rebel control, is impossible. The rebels will not accept Syrian regime traffic along these roads in any feasible scenario. So what's going on?
While both leaders know that the roads are the key to controlling Idlib (which is why Turkey has parked tanks on them), Putin knows that once rebels start attacking Syrian regime personnel transiting those roads, he will have his casus belli to seize Idlib entirely, and do so under the pretense that he has honored his bargain with Erdogan. Of course, Erdogan must also know this. His acceptance of this deal is thus a short term effort to delay an axis offensive and hope for some kind of future solution.
But Putin will be the ultimate victor here. The offensive is still coming and Idlib will still be slaughtered.