Sources in Iraq said in September that Al-Sadr had been in Iran, and it appears that this latest truce was signed in Tehran on Oct 3, when Al-Sadr was there to meet with al-Hakim. The Iranians have made clear to Al-Sadr that he must either cooperate and get his militia in line or face a massive purge led by Al-Hakim's Badr group. Al-Sadr appears to have complied.This comes via Cernig, who is skeptical. Me too. Still, as rumors go this one isn't bad, and it's far from inconceivable that this is how things played out though it doesn't necessarily mean that Sistani wasn't involved too. The truce could have had multiple brokers.
....The Iranians are also heavily invested in al-Hakim's SIIC, which they view as the main vehicle to extend Iranian influence into Iraq. Iran has traditionally played Al-Sadr and al-Hakim's factions against one another to ensure that both depend on Tehran's good graces-but that policy has been more destructive than intended. Recognizing that Al-Sadr is a force to be reckoned with, Iran has decided it will be more worthwhile to co-opt him than to challenge him in the long run though several obstacles will prevent Tehran from doing so.
As for what it means, I'll leave that to smarter people than me. Just seemed worth passing along.