The fact that Idlib will become a stumbling block in the whole tormenting Syrian process has been clear for a long time. All previous compromises and current agreements led to the fact that this province turned into the quintessence of the entire Syrian conflict, it is crammed with radicals of various kinds. And a wide variety of interests concentrated there, as well as considerations of prestige.
Now, apparently, a really turning point has come, after which the course of events can unfold sharply. Erdogan raised rates as much as possible. He does not intend to allow Damascus to regain control of Idlib; moreover, he needs a demonstration of military victory, and not another deal with Russia on demarcation lines and buffer zones. Apparently, the Turkish president really believes that we are talking about strategic issues - positioning Turkey in the Middle East as a whole and its future as an influential power. He is ready to defend the right of Ankara to resolve issues of its own "near abroad" by military means.
Prior to this, the Kurdish issue was the focus of attention, and here Russia made concessions, allowing the creation of a buffer zone and a partial cleansing of Syrian Kurdistan. Turkey does not want to agree on Idlib (for now, at least) and does not consider Afrin scenario. Ankara is ready to risk a war with the "regime" (in the terminology of the West), hoping that Russia will not fully intervene. Moscow’s restrained rhetoric in recent weeks, when the situation grew tense, was probably perceived in Ankara as evidence of unwillingness to aggravate, especially since the Russian side was constantly negotiating and making various proposals.
Erdogan is convinced that Russia should recognize its priority right in this region - after all, Turkey is a neighbor, while Russia is an external force, albeit an important one. But at the same time, he drives Moscow into a corner, testing its reliability as an ally of Damascus. But such inspections are very disliked by the Kremlin. Russia firmly adheres to the opposite position - whatever one may say, but everything happens on the internationally recognized territory of Syria, so the space for concessions pushing the neighboring country is narrow enough. Erdogan’s attempts to draw NATO and the EU into the process, forcing them to put pressure on Russia are not adding constructive spirit on the Russian side. Just recall how furious Putin was in 2015, after the downed Russian plane, Erdogan’s hasty desire to receive support and guarantees from NATO.
Be that as it may, Russian politics in Syria has come to a crucial point. Quite frankly, it is decided who is the master here. If, despite such a sharp escalation, it will be possible to avoid a direct confrontation with Turkey and return to politics in the spirit of the Astana Triangle, then the whole operation since 2015 has really brought qualitative changes to the region. And if it does not succeed, then the costs of the further course of events may block previously received dividends. The possible collapse of relations with Turkey is fraught with far-reaching consequences.