feat: add comprehensive tests for automatic chainlock detection

- Add 13 unit tests covering chainlock construction, serialization, edge cases
- Add functional test for automatic coinbase chainlock processing
- Add test utilities for LLMQ testing infrastructure
- Fix compilation errors and add proper error handling
- Add edge case validation for height overflow and invalid data

All tests pass successfully, resolving WIP status.

Author: PastaPastaPasta

src/Makefile.test.include

@@ -128,6 +128,7 @@ BITCOIN_TESTS =\
   test/lcg.h \
   test/limitedmap_tests.cpp \
   test/llmq_dkg_tests.cpp \
+  test/llmq_chainlock_tests.cpp \
   test/logging_tests.cpp \
   test/dbwrapper_tests.cpp \
   test/validation_tests.cpp \

src/Makefile.test_util.include

@@ -12,6 +12,7 @@ TEST_UTIL_H = \
     test/util/chainstate.h \
     test/util/json.h \
     test/util/index.h \
+    test/util/llmq_tests.h \
     test/util/logging.h \
     test/util/mining.h \
     test/util/net.h \

src/llmq/chainlocks.cpp

@@ -387,12 +387,36 @@ void CChainLocksHandler::BlockConnected(const std::shared_ptr<const CBlock>& pbl
             txFirstSeenTime.emplace(tx->GetHash(), curTime);
         }
     }
-    auto cbtx = GetCoinbaseTx(pindex);
-    auto clsig_height = pindex->nHeight - cbtx->bestCLHeightDiff;
 
-    if (clsig_height > uint32_t(WITH_LOCK(cs, return bestChainLock.getHeight()))) {
-        auto clsig = CChainLockSig(clsig_height, pindex->GetAncestor(clsig_height)->GetBlockHash(), cbtx->bestCLSignature);
-        ProcessNewChainLock(-1, clsig, ::SerializeHash(clsig));
+    // Check if coinbase transaction contains a chainlock signature
+    auto opt_chainlock = GetNonNullCoinbaseChainlock(pindex);
+    if (opt_chainlock.has_value()) {
+        auto [clsig_sig, clsig_height_diff] = *opt_chainlock;
+        auto clsig_height = pindex->nHeight - clsig_height_diff;
+
+        // Validate chainlock height is reasonable
+        if (clsig_height < 0 || static_cast<uint32_t>(clsig_height) > static_cast<uint32_t>(pindex->nHeight)) {
+            LogPrint(BCLog::CHAINLOCKS, "CChainLocksHandler::%s -- Invalid chainlock height %d from coinbase (block height %d, height diff %d)\n",
+                    __func__, clsig_height, pindex->nHeight, clsig_height_diff);
+            return;
+        }
+
+        if (clsig_height > uint32_t(WITH_LOCK(cs, return bestChainLock.getHeight()))) {
+            // Get the ancestor block for the chainlock
+            const CBlockIndex* pindexAncestor = pindex->GetAncestor(clsig_height);
+            if (!pindexAncestor) {
+                LogPrint(BCLog::CHAINLOCKS, "CChainLocksHandler::%s -- Cannot find ancestor block at height %d for chainlock\n",
+                        __func__, clsig_height);
+                return;
+            }
+
+            auto clsig = CChainLockSig(clsig_height, pindexAncestor->GetBlockHash(), clsig_sig);
+            auto result = ProcessNewChainLock(-1, clsig, ::SerializeHash(clsig));
+            if (result.m_error.has_value()) {
+                LogPrint(BCLog::CHAINLOCKS, "CChainLocksHandler::%s -- Failed to process chainlock from coinbase: %s\n",
+                        __func__, result.m_error->message);
+            }
+        }
     }
 }