test: add attest after upgrade test (#71)

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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Adds a flow testing attestation behavior immediately after upgrade (fail then succeed post-epoch) and wires it into mainnet-fork tests.
> 
> - **Flow tests**:
>   - Add `AttestAfterUpgradeFlow` in `src/flow_test/flows.cairo` to validate attestation immediately after upgrade:
>     - First attest via `IAttestationSafeDispatcherTrait` fails (no previous-epoch trace), then after advancing an epoch attestation succeeds and rewards equal `calculate_staker_strk_rewards_v2`.
>   - Register test `attest_after_upgrade_flow_test` in `src/flow_test/fork_test.cairo`.
> 
> <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 0becc70. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: arad-starkware

src/flow_test/flows.cairo

@@ -3,6 +3,7 @@ use core::num::traits::Zero;
 use core::num::traits::ops::pow::Pow;
 use snforge_std::{Token, TokenImpl, get_class_hash, start_cheat_block_number_global};
 use staking::attestation::attestation::Attestation::MIN_ATTESTATION_WINDOW;
+use staking::attestation::interface::IAttestationSafeDispatcherTrait;
 use staking::constants::{ALPHA, ALPHA_DENOMINATOR, K, STRK_IN_FRIS, STRK_TOKEN_ADDRESS};
 use staking::errors::{GenericError, InternalError};
 use staking::flow_test::utils::MainnetClassHashes::{
@@ -7197,6 +7198,55 @@ pub(crate) impl GetStakersAfterUpgradeFlowImpl of FlowTrait<GetStakersAfterUpgra
     }
 }
 
+/// Flow:
+/// Stake
+/// Upgrade
+/// Attempt attest - fail
+/// Advance epoch
+/// Attest - test rewards
+#[derive(Drop, Copy)]
+pub(crate) struct AttestAfterUpgradeFlow {
+    pub(crate) staker: Option<Staker>,
+}
+pub(crate) impl AttestAfterUpgradeFlowImpl of FlowTrait<AttestAfterUpgradeFlow> {
+    fn setup_v2(ref self: AttestAfterUpgradeFlow, ref system: SystemState) {
+        let amount = system.staking.get_min_stake();
+        let staker = system.new_staker(:amount);
+        system.stake(:staker, :amount, pool_enabled: false, commission: 200);
+
+        system.set_staker_for_migration(staker_address: staker.staker.address);
+        self.staker = Option::Some(staker);
+    }
+
+    #[feature("safe_dispatcher")]
+    fn test(self: AttestAfterUpgradeFlow, ref system: SystemState) {
+        let staker = self.staker.unwrap();
+        let attestation_safe = system.attestation.unwrap().safe_dispatcher();
+
+        cheat_caller_address_once(
+            contract_address: system.attestation.unwrap().address,
+            caller_address: staker.operational.address,
+        );
+        let result = attestation_safe.attest(block_hash: Zero::zero());
+        // This error is due to the staker trace having no entry for the previous epoch.
+        // Had the staker been initialized in V3, the error would have been
+        // ATTEST_WITH_ZERO_BALANCE.
+        assert_panic_with_error(:result, expected_error: "Index out of bounds");
+
+        system.advance_epoch();
+        system.advance_block_into_attestation_window(:staker);
+        system.attest(:staker);
+
+        let rewards = system.staker_claim_rewards(:staker);
+        let (expected_rewards, _) = calculate_staker_strk_rewards_v2(
+            staker_info: system.staker_info_v1(:staker),
+            staking_contract: system.staking.address,
+            minting_curve_contract: system.minting_curve.address,
+        );
+        assert!(rewards == expected_rewards);
+    }
+}
+
 /// Flow:
 /// Add tokens A and B
 /// Enable token B

src/flow_test/fork_test.cairo

@@ -444,6 +444,13 @@ fn get_stakers_after_upgrade_flow_test() {
     test_flow_mainnet(ref :flow);
 }
 
+#[test]
+#[fork("MAINNET_LATEST")]
+fn attest_after_upgrade_flow_test() {
+    let mut flow = flows::AttestAfterUpgradeFlow { staker: Option::None };
+    test_flow_mainnet(ref :flow);
+}
+
 #[test]
 #[fork("MAINNET_LATEST")]
 fn toggle_tokens_before_after_upgrade_flow_test() {