`LockAnnotation lock(::cs_main)` is a guarantee to the compiler thread analysis that `::cs_main` is locked (when it couldn't be determined otherwise).

Despite being annotated with the locking guarantee ...

https://github.com/bitcoin/bitcoin/blob/65526fc8666fef35ef908dbc225f706bef642c7e/src/interfaces/chain.cpp#L134-L138

... `getTipLocator()` reads `chainActive` (via `::ChainActive()`) without holding `cs_main`.

This can be verified by adding the following `AssertLockHeld(cs_main)`:

```
$ git diff
diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
index 59623284d..9fc693a0f 100644
--- a/src/interfaces/chain.cpp
+++ b/src/interfaces/chain.cpp
@@ -134,6 +134,7 @@ class LockImpl : public Chain::Lock
     CBlockLocator getTipLocator() override
     {
         LockAnnotation lock(::cs_main);
+        AssertLockHeld(::cs_main);
         return ::ChainActive().GetLocator();
     }
     Optional<int> findLocatorFork(const CBlockLocator& locator) override
$ make check
../build-aux/test-driver: line 107: 12881 Aborted                 "$@" > $log_file 2>&1
FAIL: qt/test/test_bitcoin-qt
```
auto locked_chain = chain().lock();
    LOCK(cs_wallet);
    CReserveKey reservekey(this);
    CTransactionRef tx_new;
    if (!CreateTransaction(*locked_chain, vecSend, tx_new, reservekey, nFeeRet, nChangePosInOut, strFailReason, coinControl, false)) {
        return false;
    }
    if (nChangePosInOut != -1) {
        tx.vout.insert(tx.vout.begin() + nChangePosInOut, tx_new->vout[nChangePosInOut]);
        
        
        reservekey.KeepKey();
    }
    
    
    for (unsigned int idx = 0; idx < tx.vout.size(); idx++) {
        tx.vout[idx].nValue = tx_new->vout[idx].nValue;
    }
    
    for (const CTxIn& txin : tx_new->vin) {
        if (!coinControl.IsSelected(txin.prevout)) {
            tx.vin.push_back(txin);
            if (lockUnspents) {
                LockCoin(txin.prevout);
            }
        }
    }
    return true;
}
static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, interfaces::Chain::Lock& locked_chain)