In Ethereum, you have entities called contracts, where contracts have their own balances, and are activated every time you send a transaction (think: money with an optional message attached) to them. The contract has 16 computational steps for free to give it wiggle room to determine whether a transaction is even worth processing; after this, every computational step that the contract takes costs it 1x BASEFEE (or more for specialized data access or crypto ops). If the contract goes bankrupt halfway through the computational process, it just stops halfway through.
How r blockchain reorgs handled? Computational steps can't be rolled back nor blockchain can be re-rolled from block 0, so u r supposed to store blockchain snapshots each N-th block, which is quite expensive.
Can't a Finney attack be combined with a very long-running transactions to DoS all nodes? If a miner earns all block fees then even without a Finney attack a malicious miner could include a lot of long-running transactions into their block to slow down processing of the next block / transactions.