Update docs vis-a-vis prohibition of RentPaying accounts (#22438)

* Rent-exempt docs for exchange integrations

* Remove discussion of rent-paying accounts from developing docs

* Improve verbiage

docs/src/developing/programming-model/accounts.md

@@ -135,72 +135,13 @@ blockchain cluster must actively maintain the data to process any future transac
 This is different from Bitcoin and Ethereum, where storing accounts doesn't
 incur any costs.
 
-The rent is debited from an account's balance by the runtime upon the first
-access (including the initial account creation) in the current epoch by
-transactions or once per an epoch if there are no transactions. The fee is
-currently a fixed rate, measured in bytes-times-epochs. The fee may change in
-the future.
-
-For the sake of simple rent calculation, rent is always collected for a single,
-full epoch. Rent is not pro-rated, meaning there are neither fees nor refunds
-for partial epochs. This means that, on account creation, the first rent
-collected isn't for the current partial epoch, but collected up front for the
-next full epoch. Subsequent rent collections are for further future epochs. On
-the other end, if the balance of an already-rent-collected account drops below
-another rent fee mid-epoch, the account will continue to exist through the
-current epoch and be purged immediately at the start of the upcoming epoch.
-
-Accounts can be exempt from paying rent if they maintain a minimum balance. This
-rent-exemption is described below.
-
-### Calculation of rent
-
-Note: The rent rate can change in the future.
-
-As of writing, the fixed rent fee is 19.055441478439427 lamports per byte-epoch
-on the testnet and mainnet-beta clusters. An [epoch](terminology.md#epoch) is
-targeted to be 2 days (For devnet, the rent fee is 0.3608183131797095 lamports
-per byte-epoch with its 54m36s-long epoch).
-
-This value is calculated to target 0.01 SOL per mebibyte-day (exactly matching
-to 3.56 SOL per mebibyte-year):
-
-```text
-Rent fee: 19.055441478439427 = 10_000_000 (0.01 SOL) * 365(approx. day in a year) / (1024 * 1024)(1 MiB) / (365.25/2)(epochs in 1 year)
-```
-
-And rent calculation is done with the `f64` precision and the final result is
-truncated to `u64` in lamports.
-
-The rent calculation includes account metadata (address, owner, lamports, etc)
-in the size of an account. Therefore the smallest an account can be for rent
-calculations is 128 bytes.
-
-For example, an account is created with the initial transfer of 10,000 lamports
-and no additional data. Rent is immediately debited from it on creation,
-resulting in a balance of 7,561 lamports:
-
-```text
-Rent: 2,439 = 19.055441478439427 (rent rate) * 128 bytes (minimum account size) * 1 (epoch)
-Account Balance: 7,561 = 10,000 (transfered lamports) - 2,439 (this account's rent fee for an epoch)
-```
-
-The account balance will be reduced to 5,122 lamports at the next epoch even if
-there is no activity:
-
-```text
-Account Balance: 5,122 = 7,561 (current balance) - 2,439 (this account's rent fee for an epoch)
-```
-
-Accordingly, a minimum-size account will be immediately removed after creation
-if the transferred lamports are less than or equal to 2,439.
+Currently, all new accounts are required to be rent-exempt.
 
 ### Rent exemption
 
-Alternatively, an account can be made entirely exempt from rent collection by
-depositing at least 2 years worth of rent. This is checked every time an
-account's balance is reduced, and rent is immediately debited once the balance
-goes below the minimum amount.
+An account is considered rent-exempt if it holds at least 2 years worth of rent.
+This is checked every time an account's balance is reduced, and transactions
+that would reduce the balance to below the minimum amount will fail.
 
 Program executable accounts are required by the runtime to be rent-exempt to
 avoid being purged.

docs/src/integrations/exchange.md

@@ -153,10 +153,9 @@ generate a Solana keypair using any of our [wallet tools](../wallet-guide/cli.md
 
 We recommend using a unique deposit account for each of your users.
 
-Solana accounts are charged [rent](developing/programming-model/accounts.md#rent) on creation and once per
-epoch, but they can be made rent-exempt if they contain 2-years worth of rent in
-SOL. In order to find the minimum rent-exempt balance for your deposit accounts,
-query the
+Solana accounts must be made rent-exempt by containing 2-years worth of
+[rent](developing/programming-model/accounts.md#rent) in SOL. In order to find
+the minimum rent-exempt balance for your deposit accounts, query the
 [`getMinimumBalanceForRentExemption` endpoint](developing/clients/jsonrpc-api.md#getminimumbalanceforrentexemption):
 
 ```bash
@@ -567,6 +566,20 @@ public class PubkeyValidator
 }
 ```
 
+## Minimum Deposit & Withdrawal Amounts
+
+Every deposit and withdrawal of SOL must be greater or equal to the minimum
+rent-exempt balance for the account at the wallet address (a basic SOL account
+holding no data), currently: 0.000890880 SOL
+
+Similarly, every deposit account must contain at least this balance.
+
+```bash
+curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc": "2.0","id":1,"method":"getMinimumBalanceForRentExemption","params":[0]}' localhost:8899
+
+{"jsonrpc":"2.0","result":890880,"id":1}
+```
+
 ## Supporting the SPL Token Standard
 
 [SPL Token](https://spl.solana.com/token) is the standard for wrapped/synthetic
@@ -750,4 +763,4 @@ Be sure to test your complete workflow on Solana devnet and testnet
 [clusters](../clusters.md) before moving to production on mainnet-beta. Devnet
 is the most open and flexible, and ideal for initial development, while testnet
 offers more realistic cluster configuration. Both devnet and testnet support a faucet,
-run `solana airdrop 1` to obtain some devnet or testnet SOL for developement and testing.
+run `solana airdrop 1` to obtain some devnet or testnet SOL for development and testing.