Merge #20035: signet: Fix uninitialized read in validation

fa723e3 Initialize default-initialized uint256 consensus params to zero explicitly (MarcoFalke)
fa729cd doc: Move assumed-values doxygen comments to header (MarcoFalke)
fa64892 signet: Fix uninitialized read in validation (MarcoFalke)

Pull request description:

ACKs for top commit:
  practicalswift:
    re-ACK fa723e3: patch still looks correct
  kallewoof:
    ReACK fa723e3
  theStack:
    re-ACK fa723e3 🍐

Tree-SHA512: db562bcc15af23bbcbf485f0bbf7564c64c144a4368230fd7682e8861d9500f6f5240351e31c560140df43b2e8456eafd9d27d1e8dd682b20afcc279a39dc329

Author: laanwj

src/chainparams.cpp

@@ -91,10 +91,7 @@ class CMainParams : public CChainParams {
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nStartTime = 1199145601; // January 1, 2008
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nTimeout = 1230767999; // December 31, 2008
 
-        // The best chain should have at least this much work.
         consensus.nMinimumChainWork = uint256S("0x00000000000000000000000000000000000000000e1ab5ec9348e9f4b8eb8154");
-
-        // By default assume that the signatures in ancestors of this block are valid.
         consensus.defaultAssumeValid = uint256S("0x0000000000000000000f2adce67e49b0b6bdeb9de8b7c3d7e93b21e7fc1e819d"); // 623950
 
         /**
@@ -207,10 +204,7 @@ class CTestNetParams : public CChainParams {
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nStartTime = 1199145601; // January 1, 2008
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nTimeout = 1230767999; // December 31, 2008
 
-        // The best chain should have at least this much work.
         consensus.nMinimumChainWork = uint256S("0x0000000000000000000000000000000000000000000001495c1d5a01e2af8a23");
-
-        // By default assume that the signatures in ancestors of this block are valid.
         consensus.defaultAssumeValid = uint256S("0x000000000000056c49030c174179b52a928c870e6e8a822c75973b7970cfbd01"); // 1692000
 
         pchMessageStart[0] = 0x0b;
@@ -297,6 +291,8 @@ class SigNetParams : public CChainParams {
             }
             bin = ParseHex(signet_challenge[0]);
 
+            consensus.nMinimumChainWork = uint256{};
+            consensus.defaultAssumeValid = uint256{};
             m_assumed_blockchain_size = 0;
             m_assumed_chain_state_size = 0;
             chainTxData = ChainTxData{
@@ -315,7 +311,9 @@ class SigNetParams : public CChainParams {
         consensus.signet_blocks = true;
         consensus.signet_challenge.assign(bin.begin(), bin.end());
         consensus.nSubsidyHalvingInterval = 210000;
+        consensus.BIP16Exception = uint256{};
         consensus.BIP34Height = 1;
+        consensus.BIP34Hash = uint256{};
         consensus.BIP65Height = 1;
         consensus.BIP66Height = 1;
         consensus.CSVHeight = 1;
@@ -326,6 +324,7 @@ class SigNetParams : public CChainParams {
         consensus.fPowNoRetargeting = false;
         consensus.nRuleChangeActivationThreshold = 1916;
         consensus.nMinerConfirmationWindow = 2016;
+        consensus.MinBIP9WarningHeight = 0;
         consensus.powLimit = uint256S("00000377ae000000000000000000000000000000000000000000000000000000");
         consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].bit = 28;
         consensus.vDeployments[Consensus::DEPLOYMENT_TESTDUMMY].nStartTime = 1199145601; // January 1, 2008
@@ -394,11 +393,8 @@ class CRegTestParams : public CChainParams {
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nStartTime = Consensus::BIP9Deployment::ALWAYS_ACTIVE;
         consensus.vDeployments[Consensus::DEPLOYMENT_TAPROOT].nTimeout = Consensus::BIP9Deployment::NO_TIMEOUT;
 
-        // The best chain should have at least this much work.
-        consensus.nMinimumChainWork = uint256S("0x00");
-
-        // By default assume that the signatures in ancestors of this block are valid.
-        consensus.defaultAssumeValid = uint256S("0x00");
+        consensus.nMinimumChainWork = uint256{};
+        consensus.defaultAssumeValid = uint256{};
 
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0xbf;

src/consensus/params.h

@@ -79,7 +79,9 @@ struct Params {
     int64_t nPowTargetSpacing;
     int64_t nPowTargetTimespan;
     int64_t DifficultyAdjustmentInterval() const { return nPowTargetTimespan / nPowTargetSpacing; }
+    /** The best chain should have at least this much work */
     uint256 nMinimumChainWork;
+    /** By default assume that the signatures in ancestors of this block are valid */
     uint256 defaultAssumeValid;
 
     /**