>A tactical nuclear weapon detonation over Ukrainian combat units that disrupts Ukrainian offensive, western military support for Ukraine, and global markets suffer lasting disruption.

A single tactical nuke would have virtually no impact on Ukrainian military operations. It would only affect a few square km, maybe a battalion strength unit. To decisively influence a significant front like Kherson would take at least a handful of them. To relieve pressure along the whole front would take dozens. Strategic warheads used on the front would do more, but then the radiation and fallout effects would also impact Russian units, and Russia itself. there's also no way to use and EMP pulse to impair Ukrainian front line units without also impairing Russian front line units.

>Western coalitions have disrupted the Russian economy with sanctions, but China/India provide two major energy export customers.

Using nukes would remove all the remaining support Russia has, including that from China and India in terms of trade. It's likely the west would impose a total blockade and interdiction of all Russian ports, sea traffic and air transport anyway.