Not much point in signing a 25-year pact with a regime that'll be gone in 2....
I have always laughed at those who mention a coming U.S.-China conflict with confidence as if such a showdown would actually occur. But a U.S. invasion of Iran will definitely face elements of Chinese military (special forces?)on the field, as Chinese are most serious about their oil flows, it's one of the few things they would actually be willing to go to arms against the U.S. for. I wouldn't be surprised at all if China will deploy military units to protect its exploration sites in Iran, in addition to the Iranian forces that will surely be on site as well.