Disallow closing the top stake account

api/src/error.rs

@@ -23,6 +23,10 @@ pub enum OreError {
     ToleranceOverflow = 7,
     #[error("The maximum supply has been reached")]
     MaxSupply = 8,
+    #[error("This account cannot be closed because it's the top staker")]
+    CannotClose = 9,
+    #[error("This account cannot be crowned because its last stake was too recent")]
+    CannotCrown = 10,
 }
 
 impl From<OreError> for ProgramError {

program/src/close.rs

@@ -1,4 +1,8 @@
-use ore_api::{loaders::*, state::Proof};
+use ore_api::{
+    error::OreError,
+    loaders::*,
+    state::{Config, Proof},
+};
 use solana_program::{
     account_info::AccountInfo, entrypoint::ProgramResult, program_error::ProgramError,
     pubkey::Pubkey, system_program,
@@ -20,13 +24,21 @@ pub fn process_close<'a, 'info>(
     _data: &[u8],
 ) -> ProgramResult {
     // Load accounts
-    let [signer, proof_info, system_program] = accounts else {
+    let [signer, config_info, proof_info, system_program] = accounts else {
         return Err(ProgramError::NotEnoughAccountKeys);
     };
     load_signer(signer)?;
+    load_config(config_info, false)?;
     load_proof(proof_info, signer.key, true)?;
     load_program(system_program, system_program::id())?;
 
+    // Validate the account is not the crowned top staker.
+    let config_data = config_info.data.borrow();
+    let config = Config::try_from_bytes(&config_data)?;
+    if config.top_staker.eq(proof_info.key) {
+        return Err(OreError::CannotClose.into());
+    }
+
     // Validate balance is zero
     let proof_data = proof_info.data.borrow();
     let proof = Proof::try_from_bytes(&proof_data)?;