We have had comfortable relations with the Russians in Syria since Trump took over. No agreements, just military to military unwritten understandings.
Now, as far as Iran is concerned? No way.
Interesting. As long as it results into Kurdistan. Big chunk out of Iran. We owe them a punch in the nose.
I think this foreshadows what is likely - the Regime and especially Iranian surrogates will try to attack or gradually undermine the Kurds on the ground, but the Russians will generally refrain from direct engagement against the Kurds.
As long as the Kurds have American air support, the Russians kind of have to refrain from combat against the Kurds anyhow - just the occasional airstrike excused as a mistake.
The Russians definitely do want to cultivate Kurds long term as a chip against Turkey, but they will balances their equity with the Iranians and Syrian Regime.