prposal for formal lookback limits

[vyzo]

[Stebalien]

1. If we actually need to set limits, this would need to be a FIP and would need to be enforced in actors. However, I think we just need to figure out what the existing limits are.
2. In terms of state lookback: We lookback one chain finality (900 epochs) for the block miner's worker key & power. I'm not aware of any other lookback.
3. In terms of chain lookback (for randomness/beacons), the answer is likely a month plus a bit. But really, there's no reason not to keep the entire chain (not the messages, just the block headers).

So the answer is: 900 epochs (1800-2000 to be safe) plus the chain headers.

[Stebalien]

Anyways, what is a "booster". Are you referring to public nodes for light clients? Those nodes can probably reject all requests that try to access anything not in the current tipset. They can also refuse to execute any slashing messages not included in a block.