Have you considered that Lebanon and Israel would choose not to escalate? We all agree that the main blast was an accident. If Israel was responsible for the initial fire in the warehouse next door - The immediate suspicion was that Israel had staged an air strike against a consignment of weaponry destined for the Iran-backed Hezbollah and it's not like they don't have previous form for blowing up warehouses they believe are arms caches (Syria) - the result could be a war with Hezbollah and Hezbollah’s patron Iran that could even embroil the United States and other nations in a vast Middle East conflagration.
Interesting conspiracy theories.
Now here is the reality though. Lebanons regime has been on the brink of collapse and change even last year. With this happening it only highlighted the problems within the Lebanese society: incompetence, corruption, and abuse of business by structures like tribes or hezbollah etc.
As an example, you can see Macrons visit and people flowing to him. This shows that the French mandate is being remembered kindly nowadays compared to the current independent rule.
The better question is why did Lebanon not use Israel as a scapegoat anyways. As i said before, it is a very easy scapegoat. I think that the protests last year had a lot to do with it. The protests were basically stopped by the pandemic and not change as i understand and the ISrael card was used a lot. Now though, using it again probably will be detrimental and might become a typing point if they don't acknowledge the corruption and incompetence with such a large tragedy.
As for your conspiracy theory. Even if they blame Israel for political reasons then Hezbollah is just going to have some minor skirmishes at best. Or fire some rockets. There is no realistic way that Iran or Lebanon can face Israel in a war. Israel will probably win since Lebanon has a border with Israel while Iran does not. Otherwise, if even some miracle happens, US will just step in. All sides realise this so no war is going to happen. Lebanon and Iran do not have a way to fight Israel in the open field so at best they can use guerilla like tactics. May be Iran can if Israel directly invades Iranian territory but Israel doesn't have a border nor is it even interested in directly invading Iran itself.