Suppose I have a 2 txs A and B where B depends on A succeeding.
If both A & B are included in the same block/slot, this implies there may be some partial ordering between txs in this block that needs to be enforced for them to succeed.
Does this mean that the leader tries to order txs in the block when proposing? If yes, is this ordering of txs surfaced at the RPC level (eg maybe a "tx slot" inside the block)?
The leader validator that produces the block does in fact order the transactions in whichever order they want, based on account read / write locks, affected programs, etc. Typically, it will go first-come, first-serve, but in time, as MEV is added to validators, this will no longer be the case, and they can enforce their own constraints.
At the RPC level, the order of transactions in the block is the order in which they were executed. The explorer surfaces this with a "#" column, e.g. https://explorer.solana.com/block/137445155?filter=all