fix: validate sysvar data before refreshing the sysvar cache

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Keep the sysvar cache unchanged when `LiteSVM::set_account` rejects invalid sysvar data. The rejected write used to drop that sysvar from the cache, so the next transaction panicked ([#436](https://github.com/LiteSVM/litesvm/pull/436)).
 - Return an error instead of panicking from `litesvm_token::get_spl_account` (and the `*Checked` token helpers that read the mint through it) when the account data is shorter than the requested state ([#433](https://github.com/LiteSVM/litesvm/pull/433)).
 
 ## [0.18.0] - 2026-10-09

crates/litesvm/src/accounts_db.rs

@@ -60,6 +60,7 @@ fn handle_sysvar<T>(
 where
     T: Sysvar + DeserializeOwned<Dst = T>,
 {
+    let _parsed = T::deserialize_from(account.data()).map_err(|_| err_variant)?;
     cache.reset();
     cache.fill_missing_entries(|pubkey, set_sysvar| {
         if *pubkey == address {
@@ -68,7 +69,6 @@ where
             set_sysvar(acc.data())
         }
     });
-    let _parsed = T::deserialize_from(account.data()).map_err(|_| err_variant)?;
     Ok(())
 }
 

crates/litesvm/tests/rent.rs

@@ -6,7 +6,10 @@ use {
         FeatureSet,
     },
     litesvm::LiteSVM,
+    solana_account::Account,
+    solana_address::Address,
     solana_rent::{Rent, DEFAULT_LAMPORTS_PER_BYTE},
+    solana_sdk_ids::sysvar,
 };
 
 fn rent_with(feature_set: FeatureSet) -> Rent {
@@ -84,3 +87,20 @@ fn legacy_rent_representation_without_the_threshold_feature() {
         Rent::default().minimum_balance(123)
     );
 }
+
+#[test]
+fn rejected_rent_write_keeps_the_cached_rent() {
+    let mut svm = LiteSVM::new();
+    let min_balance = svm.minimum_balance_for_rent_exemption(0);
+    let invalid_rent = Account {
+        lamports: 1,
+        data: vec![0; 3],
+        owner: sysvar::id(),
+        executable: false,
+        rent_epoch: 0,
+    };
+
+    assert!(svm.set_account(sysvar::rent::id(), invalid_rent).is_err());
+    assert_eq!(svm.minimum_balance_for_rent_exemption(0), min_balance);
+    svm.airdrop(&Address::new_unique(), min_balance).unwrap();
+}