fix: intermittent error in feature_dip3_v19.py

It can happen on Regtest or Devnet if v20 is just activated but the best
chainlock is still in legacy (pre-v19) scheme.

It causes errors on CI similar to this one:

    2025-05-31T10:28:49.821000Z TestFramework (INFO): Checking that protxs with duplicate EvoNodes fields are rejected
    2025-05-31T10:29:50.653000Z TestFramework (INFO): dynamically_prepare_masternode failed
    2025-05-31T10:30:50.784000Z TestFramework (ERROR): Assertion failed
    Traceback (most recent call last):
      File "DASH/test/functional/test_framework/test_framework.py", line 162, in main
        self.run_test()
      File "DASH/test/functional/feature_dip3_v19.py", line 87, in run_test
        self.dynamically_evo_update_service(evo_info_0, 8)
      File "DASH/test/functional/test_framework/test_framework.py", line 1384, in dynamically_evo_update_service
        tip = self.generate(self.nodes[0], 1)[0]
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "DASH/test/functional/test_framework/test_framework.py", line 805, in generate
        sync_fun() if sync_fun else self.sync_all()
                                    ^^^^^^^^^^^^^^^
      File "DASH/test/functional/test_framework/test_framework.py", line 874, in sync_all
        self.sync_blocks(nodes)
      File "DASH/test/functional/test_framework/test_framework.py", line 840, in sync_blocks
        raise AssertionError("Block sync timed out after {}s:{}".format(
    AssertionError: Block sync timed out after 60s:
      '4227eea732e686fcf608bcbc5525a02336bb69c2eed70e8a59d6439b2122190f'
      '4227eea732e686fcf608bcbc5525a02336bb69c2eed70e8a59d6439b2122190f'
      '4227eea732e686fcf608bcbc5525a02336bb69c2eed70e8a59d6439b2122190f'
      '4227eea732e686fcf608bcbc5525a02336bb69c2eed70e8a59d6439b2122190f'
      '4227eea732e686fcf608bcbc5525a02336bb69c2eed70e8a59d6439b2122190f'
      '4227eea732e686fcf608bcbc5525a02336bb69c2eed70e8a59d6439b2122190f'
      '0ade04ee0ae89d1168792a65c28956557c9f2991d141180b9faf7a9ae986cf24'
    2025-05-31T10:30:50.837000Z TestFramework (INFO): Stopping nodes

While underlying error is `bad-cbtx-invalid-clsig`:

     2025-05-31T10:28:49.932591Z [util/system.h:57] [error] ERROR: ConnectBlock(DASH): ProcessSpecialTxsInBlock for block 4f8767d0ad2e7c8882ba4b2819a1d8eb29fbc608ff8201ed1c857d6d3ec51cc9 failed with bad-cbtx-invalid-clsig
     2025-05-31T10:28:49.932632Z [validationinterface.cpp:254] [BlockChecked] [validation] BlockChecked: block hash=4f8767d0ad2e7c8882ba4b2819a1d8eb29fbc608ff8201ed1c857d6d3ec51cc9 state=bad-cbtx-invalid-clsig
     2025-05-31T10:28:49.932660Z [validation.cpp:1634] [InvalidChainFound] InvalidChainFound: invalid block=4f8767d0ad2e7c8882ba4b2819a1d8eb29fbc608ff8201ed1c857d6d3ec51cc9  height=202  log2_work=8.665336  date=2014-12-04T17:46:38Z
     2025-05-31T10:28:49.932667Z [validation.cpp:1639] [InvalidChainFound] InvalidChainFound:  current best=0ade04ee0ae89d1168792a65c28956557c9f2991d141180b9faf7a9ae986cf24  height=201  log2_work=8.658211  date=2014-12-04T17:36:30Z

Author: knst

src/chainparams.cpp

@@ -925,7 +925,11 @@ class CRegTestParams : public CChainParams {
         UpdateLLMQTestParametersFromArgs(args, Consensus::LLMQType::LLMQ_TEST_INSTANTSEND);
         UpdateLLMQTestParametersFromArgs(args, Consensus::LLMQType::LLMQ_TEST_PLATFORM);
         UpdateLLMQInstantSendDIP0024FromArgs(args);
+        // V20 adds CL signature to CbTx; V19 switches BLS scheme from legacy to Basic.
+        assert(consensus.V20Height >= consensus.V19Height);
+        // V20 features for CbTx (credit pool, CL) have no meaning without masternodes
         assert(consensus.V20Height >= consensus.DIP0003Height);
+        // MN_RR reallocate part of reward to CreditPool which exits since V20
         assert(consensus.MN_RRHeight >= consensus.V20Height);
     }
 

src/evo/cbtx.h

@@ -51,6 +51,9 @@ class CCbTx
             READWRITE(obj.merkleRootQuorums);
             if (obj.nVersion >= Version::CLSIG_AND_BALANCE) {
                 READWRITE(COMPACTSIZE(obj.bestCLHeightDiff));
+                // TODO: BLS scheme here should be enforced to BASIC
+                // on devnet / regtest with late v19 activation an old CL with
+                // legacy scheme could get to CbTx and cause Invalid Block errors
                 READWRITE(obj.bestCLSignature);
                 READWRITE(obj.creditPoolBalance);
             }

test/functional/feature_dip3_v19.py

@@ -47,6 +47,7 @@ def set_test_params(self):
             '-testactivationheight=v19@200',
         ]] * 6
         self.set_dash_test_params(6, 5, evo_count=2, extra_args=self.extra_args)
+        self.delay_v20_and_mn_rr(height=260)
 
 
     def run_test(self):
@@ -104,6 +105,11 @@ def run_test(self):
             new_mn = self.dynamically_add_masternode(evo=False, rnd=(10 + i))
             assert new_mn is not None
 
+        self.log.info("Chainlocks in CbTx can be only in Basic scheme. Wait one...")
+        self.wait_until(lambda: self.nodes[0].getbestchainlock()['height'] > 200)
+        self.log.info(f"block {self.nodes[0].getbestchainlock()['height']} is chainlocked after v19 activation")
+
+        self.activate_by_name('v20', expected_activation_height=260)
         # mine more quorums and make sure everything still works
         prev_quorum = None
         for _ in range(5):