chainparams: Handle Testnet4 in GetNetworkForMagic #30625

style-nit: I know you copied this from the surrounding code, but creating a copy is not needed to compare two const references, and if the size of the second range in std::equal is different, the result is either wrong or undefined behavior (UB/uninitialized read). See also the notes section (https://en.cppreference.com/w/cpp/algorithm/equal#Notes), which says "... When comparing entire containers for equality, operator== for the corresponding container are usually preferred".

So that'd be:

diff --git a/src/kernel/chainparams.cpp b/src/kernel/chainparams.cpp
index d0de3a4eab..c8522aa314 100644
--- a/src/kernel/chainparams.cpp
+++ b/src/kernel/chainparams.cpp
@@ -688,7 +688,7 @@ std::optional<ChainType> GetNetworkForMagic(const MessageStartChars& message)
     const auto regtest_msg = CChainParams::RegTest({})->MessageStart();
     const auto signet_msg = CChainParams::SigNet({})->MessageStart();
 
-    if (std::equal(message.begin(), message.end(), mainnet_msg.data())) {
+    if (message == CChainParams::Main()->MessageStart()) {
         return ChainType::MAIN;
     } else if (std::equal(message.begin(), message.end(), testnet_msg.data())) {
         return ChainType::TESTNET;

An alternative would be to use std::ranges::equal https://en.cppreference.com/w/cpp/algorithm/ranges/equal or the std::equal overload that takes 4 iterators.