`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
```
Chain& m_chain;
    Chain::Notifications* m_notifications;
};
class RpcHandlerImpl : public Handler
{
public:
    RpcHandlerImpl(const CRPCCommand& command) : m_command(command), m_wrapped_command(&command)
    {
        m_command.actor = [this](const JSONRPCRequest& request, UniValue& result, bool last_handler) {
            if (!m_wrapped_command) return false;
            try {
                return m_wrapped_command->actor(request, result, last_handler);
            } catch (const UniValue& e) {
                
                
                
                if (!last_handler) {
                    const UniValue& code = e["code"];
                    if (code.isNum() && code.get_int() == RPC_WALLET_NOT_FOUND) {
                        return false;
                    }
                }
                throw;
            }
        };
        ::tableRPC.appendCommand(m_command.name, &m_command);
    }
    void disconnect() override final