init: Delay RPC block notif until warmup finished

Summary:
Partial backport of [[bitcoin/bitcoin#23280 | core#23280]]:
bitcoin/bitcoin@2414ebc

Test Plan:
  ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D12576

Author: dongcarl

src/init.cpp

@@ -2911,7 +2911,17 @@ bool AppInitMain(Config &config, RPCServer &rpcServer,
 
     // Step 13: finished
 
+    // At this point, the RPC is "started", but still in warmup, which means it
+    // cannot yet be called. Before we make it callable, we need to make sure
+    // that the RPC's view of the best block is valid and consistent with
+    // ChainstateManager's ActiveTip.
+    //
+    // If we do not do this, RPC's view of the best block will be height=0 and
+    // hash=0x0. This will lead to erroroneous responses for things like
+    // waitforblockheight.
+    RPCNotifyBlockChange(chainman.ActiveTip());
     SetRPCWarmupFinished();
+
     uiInterface.InitMessage(_("Done loading").translated);
 
     for (const auto &client : node.chain_clients) {

src/node/chainstate.cpp

@@ -7,7 +7,6 @@
 #include <chainparams.h>
 #include <config.h>
 #include <node/blockstorage.h>
-#include <rpc/blockchain.h>
 #include <shutdown.h>
 #include <util/time.h>
 #include <validation.h>
@@ -154,7 +153,6 @@ VerifyLoadedChainstate(ChainstateManager &chainman, bool fReset,
         for (CChainState *chainstate : chainman.GetAll()) {
             if (!is_coinsview_empty(chainstate)) {
                 const CBlockIndex *tip = chainstate->m_chain.Tip();
-                RPCNotifyBlockChange(tip);
                 if (tip && tip->nTime > GetTime() + MAX_FUTURE_BLOCK_TIME) {
                     return ChainstateLoadVerifyError::ERROR_BLOCK_FROM_FUTURE;
                 }