fix(quest-engine): prevent duplicate explore quest payouts

contracts/Cargo.toml

@@ -10,7 +10,9 @@ members = [
 resolver = "2"
 
 [workspace.dependencies]
-soroban-sdk = "23"
+soroban-sdk = "23.0.0"
 
 [profile.release]
 overflow-checks = true
+
+

contracts/quest-engine/src/lib.rs

@@ -579,6 +579,7 @@ impl QuestEngineContract {
     /// * If admin does not match stored admin
     /// * If quest is not found
     /// * If quest type is not Explore
+    /// * If learner has already been verified for this quest
     /// * If contract is not initialized
     pub fn verify_explore_quest(env: Env, admin: Address, learner: Address, quest_id: u32) {
         // 1. admin.require_auth()
@@ -605,22 +606,31 @@ impl QuestEngineContract {
             "Not an Explore quest"
         );
 
-        // 5. Get reward pool address and create client
+        // 5.  NEW: Check if learner was already verified for this quest
+        let verification_key = DataKey::ExploreVerification(learner.clone(), quest_id);
+        if env.storage().persistent().has(&verification_key) {
+            panic!("Learner already verified for this quest");
+        }
+
+        // 6. Get reward pool address and create client
         let reward_pool_address: Address = env
             .storage()
             .instance()
             .get(&DataKey::RewardPool)
             .expect("Not initialized");
         let reward_pool_client = RewardPoolClient::new(&env, &reward_pool_address);
 
-        // 6. Distribute reward from RewardPool
+        // 7. Distribute reward from RewardPool
         reward_pool_client.distribute_reward(
             &env.current_contract_address(),
             &learner,
             &quest.reward_amount,
         );
 
-        // 7. Emit ExploreQuestVerified event
+        // 8.   NEW: Persist the verification marker after successful payout
+        env.storage().persistent().set(&verification_key, &true);
+
+        // 9. Emit ExploreQuestVerified event
         ExploreQuestVerified {
             admin,
             learner,
@@ -629,6 +639,11 @@ impl QuestEngineContract {
         }
         .publish(&env);
     }
+
+    pub fn is_explore_verified(env: Env, learner: Address, quest_id: u32) -> bool {
+        let key = DataKey::ExploreVerification(learner, quest_id);
+        env.storage().persistent().get(&key).unwrap_or(false)
+    }
 }
 
 #[cfg(test)]