feat: Fix geth prestate filtering for prefunded creations (#383)

This aims at resolving issues mentioned in #382 , typically this one :
<img width="1818" height="694" alt="image"
src="https://github.com/user-attachments/assets/51b82944-c711-421b-8479-05095ae9bbce"
/>

To fix this , what i did was : 
- Keep track of addresses that are marked as Create and were truly empty
in the database snapshot. Only these addresses are filtered from the
prestate diff so prefunded contract deployments remain visible.

- Introduce account_was_empty helper to avoid re-computing the emptiness
check and add a regression test
(prestate_diff_keeps_prefunded_created_accounts) that covers a prefunded
creation vs. a true empty-address creation.

cc @mattsse  Please check it out if it resolves 

should close this one paradigmxyz/reth#19703

---------

Co-authored-by: Matthias Seitz <[email protected]>

Author: 0xKarl98

src/tracing/builder/geth.rs

@@ -22,7 +22,7 @@ use revm::{
     bytecode::opcode,
     context_interface::result::{HaltReasonTr, ResultAndState},
     primitives::KECCAK_EMPTY,
-    state::EvmState,
+    state::{AccountInfo, EvmState},
     DatabaseRef,
 };
 
@@ -318,7 +318,11 @@ impl<'a> GethTraceBuilder<'a> {
             state_diff.pre.insert(addr, pre_state);
 
             // determine the change type
-            let pre_change = if changed_acc.is_created() {
+            // if the account was created _and_ not empty we need to treat it as modified,
+            // so that it is retained later in `diff_traces`
+            // See <https://etherscan.io/tx/0x391f4b6a382d3bcc3120adc2ea8c62003e604e487d97281129156fd284a1a89d>
+            // <https://github.com/paradigmxyz/reth/issues/19703#issuecomment-3527067849>
+            let pre_change = if changed_acc.is_created() && account_was_empty(&db_acc) {
                 AccountChangeKind::Create
             } else {
                 AccountChangeKind::Modify
@@ -567,3 +571,60 @@ impl<'a> GethTraceBuilder<'a> {
         }
     }
 }
+
+fn account_was_empty(account: &AccountInfo) -> bool {
+    account.balance.is_zero() && account.nonce == 0 && account.code_hash == KECCAK_EMPTY
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use alloy_primitives::{address, U256};
+    use revm::{
+        database::CacheDB,
+        database_interface::EmptyDB,
+        state::{Account, AccountInfo},
+    };
+
+    #[test]
+    fn prestate_diff_keeps_prefunded_created_accounts() {
+        let mut state = EvmState::default();
+        let prefunded_addr = address!("1000000000000000000000000000000000000001");
+        let empty_addr = address!("2000000000000000000000000000000000000002");
+
+        let mut prefunded_account = Account::default();
+        prefunded_account.mark_created();
+        prefunded_account.info.balance = U256::from(1);
+        prefunded_account.info.nonce = 1;
+        state.insert(prefunded_addr, prefunded_account);
+
+        let mut empty_account = Account::default();
+        empty_account.mark_created();
+        empty_account.info.nonce = 1;
+        state.insert(empty_addr, empty_account);
+
+        let mut db = CacheDB::new(EmptyDB::default());
+        db.insert_account_info(
+            prefunded_addr,
+            AccountInfo { balance: U256::from(10), ..Default::default() },
+        );
+
+        let builder = GethTraceBuilder::new(Vec::new());
+        let frame =
+            builder.geth_prestate_diff_traces(&state, db, false, false).expect("diff frame");
+
+        match frame {
+            PreStateFrame::Diff(diff) => {
+                assert!(
+                    diff.pre.contains_key(&prefunded_addr),
+                    "prefunded contract must remain in prestate diff"
+                );
+                assert!(
+                    !diff.pre.contains_key(&empty_addr),
+                    "contracts created on empty addresses are still filtered out"
+                );
+            }
+            _ => panic!("expected diff prestate frame"),
+        }
+    }
+}