`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& amount = m_amounts[type];
    if (recalculate || !amount.m_cached[filter]) {
        amount.Set(filter, type == DEBIT ? pwallet->GetDebit(*tx, filter) : pwallet->GetCredit(*tx, filter));
    }
    return amount.m_value[filter];
}
CAmount CWalletTx::GetDebit(const isminefilter& filter) const
{
    if (tx->vin.empty())
        return 0;
    CAmount debit = 0;
    if (filter & ISMINE_SPENDABLE) {
        debit += GetCachableAmount(DEBIT, ISMINE_SPENDABLE);
    }
    if (filter & ISMINE_WATCH_ONLY) {
        debit += GetCachableAmount(DEBIT, ISMINE_WATCH_ONLY);
    }
    return debit;
}
CAmount CWalletTx::GetCredit(interfaces::Chain::Lock& locked_chain, const isminefilter& filter) const