pruning info

docs/architecture/adr-034-account-rekeying.md

@@ -43,13 +43,16 @@ The MsgChangePubKey transaction needs to be signed by the existing pubkey in sta
 
 Once, approved, the handler for this message type, which takes in the AccountKeeper, will update the in-state pubkey for the account and replace it with the pubkey from the Msg.
 
-Because an account can no longer be pruned from state once its pubkey has changed, we can charge an additional gas fee for this operation to compensate for this this externality (this bound gas amount is configured as parameter `PubKeyChangeCost`). The bonus gas is charged inside the handler, using the `ConsumeGas` function.
+
+An account that has had its pubkey changed cannot be automatically pruned from state.  This is because if pruned, the original pubkey of the account would be needed to recreate the same address, but the owner of the address may not have the original pubkey anymore.  Currently, we do not automatically prune any accounts anyways, but we would like to keep this option open the road (this is the purpose of account numbers).  To resolve this, we charge an additional gas fee for this operation to compensate for this this externality (this bound gas amount is configured as parameter `PubKeyChangeCost`). The bonus gas is charged inside the handler, using the `ConsumeGas` function.  Furthermore, in the future, we can allow accounts that have rekeyed manually prune themselves using a new Msg type such as `MsgDeleteAccount`.  Manually pruning accounts can give a gas refund as an incentive for performing the action.
+
 
 ```go
 	amount := ak.GetParams(ctx).PubKeyChangeCost
 	ctx.GasMeter().ConsumeGas(amount, "pubkey change fee")
 ```
 
+
 Everytime a key for an address is changed, we will store a log of this change in the state of the chain, thus creating a stack of all previous keys for an address and the time intervals for which they were active.  This allows dapps and clients to easily query past keys for an account which may be useful for features such as verifying timestamped off-chain signed messages.
 
 
@@ -65,7 +68,7 @@ Everytime a key for an address is changed, we will store a log of this change in
 Breaks the current assumed relationship between address and pubkeys as H(pubkey) = address. This has a couple of consequences.
 
 * This makes wallets that support this feature more complicated. For example, if an address on chain was updated, the corresponding key in the CLI wallet also needs to be updated.
-* We cannot prune accounts with 0 balance that have had their pubkey changed. This is because if pruned, the original pubkey of the account would be needed to recreate the same address, but the owner of the address may not have the original pubkey anymore.  Currently, we do not automatically prune accounts anyways, but the purpose of account numbers is to allow for this down the road.  One way to allow accounts that have had their pubkeys changed is to allow their owners to manually prune their accounts using a new Msg type such as `MsgDeleteAccount`.  Manually pruning accounts can give a gas refund as an incentive for performing the action.
+* Cannot automatically prune accounts with 0 balance that have had their pubkey changed.
 
 
 ### Neutral