fix: add fatal log on amendment-blocked shutdown

- signalStop() for graceful shutdown when unsupported amendment activates
- early shutdown ~1 minute before expected activation to avoid race
- try/catch in switchLastClosedLedger to survive unknown field crashes
  during shutdown window
- show amendment warning to all RPC users, not just admin

Fixes: #706

src/xrpld/app/ledger/detail/LedgerMaster.cpp

@@ -310,12 +310,28 @@ LedgerMaster::setValidLedger(std::shared_ptr<Ledger const> const& l)
             if (auto const first =
                     app_.getAmendmentTable().firstUnsupportedExpected())
             {
-                JLOG(m_journal.error()) << "One or more unsupported amendments "
-                                           "reached majority. Upgrade before "
-                                        << to_string(*first)
-                                        << " to prevent your server from "
-                                           "becoming amendment blocked.";
-                app_.getOPs().setAmendmentWarned();
+                using namespace std::chrono_literals;
+                auto const now = app_.timeKeeper().closeTime();
+                if (*first > now && (*first - now) <= 1min)
+                {
+                    // Shut down just before the amendment activates to
+                    // avoid processing ledgers with unknown fields.
+                    JLOG(m_journal.error())
+                        << "Unsupported amendment activating imminently "
+                           "at "
+                        << to_string(*first) << ". Shutting down.";
+                    app_.getOPs().setAmendmentBlocked();
+                }
+                else
+                {
+                    JLOG(m_journal.error())
+                        << "One or more unsupported amendments "
+                           "reached majority. Upgrade before "
+                        << to_string(*first)
+                        << " to prevent your server from "
+                           "becoming amendment blocked.";
+                    app_.getOPs().setAmendmentWarned();
+                }
             }
             else
                 app_.getOPs().clearAmendmentWarned();

src/xrpld/app/misc/NetworkOPs.cpp

@@ -1634,6 +1634,16 @@ NetworkOPsImp::setAmendmentBlocked()
 {
     amendmentBlocked_ = true;
     setMode(OperatingMode::CONNECTED);
+    if (!app_.config().standalone())
+    {
+        JLOG(m_journal.fatal())
+            << "One or more unsupported amendments activated. "
+               "Shutting down. Upgrade the server to remain "
+               "compatible with the network.";
+        app_.signalStop(
+            "One or more unsupported amendments activated. "
+            "Server must be upgraded to remain compatible with the network.");
+    }
 }
 
 inline bool
@@ -1789,8 +1799,23 @@ NetworkOPsImp::switchLastClosedLedger(
 
     clearNeedNetworkLedger();
 
-    // Update fee computations.
-    app_.getTxQ().processClosedLedger(app_, *newLCL, true);
+    // Update fee computations. May throw if the ledger contains
+    // transactions with fields unknown to this binary (e.g. after an
+    // unsupported amendment activates). Catch to allow graceful shutdown.
+    //@@start process-closed-ledger-catch
+    try
+    {
+        app_.getTxQ().processClosedLedger(app_, *newLCL, true);
+    }
+    catch (std::runtime_error const& e)
+    {
+        if (!amendmentBlocked_)
+            throw;
+        JLOG(m_journal.error())
+            << "Failed to process closed ledger: " << e.what();
+        return;
+    }
+    //@@end process-closed-ledger-catch
 
     // Caller must own master lock
     {
@@ -2449,7 +2474,7 @@ NetworkOPsImp::getServerInfo(bool human, bool admin, bool counters)
                 "may be incorrectly configured or some [validator_list_sites] "
                 "may be unreachable.";
         }
-        if (admin && isAmendmentWarned())
+        if (isAmendmentWarned())
         {
             Json::Value& w = warnings.append(Json::objectValue);
             w[jss::id] = warnRPC_UNSUPPORTED_MAJORITY;
@@ -2893,6 +2918,7 @@ NetworkOPsImp::pubLedger(std::shared_ptr<ReadView const> const& lpAccepted)
     // Ledgers are published only when they acquire sufficient validations
     // Holes are filled across connection loss or other catastrophe
 
+    //@@start pubLedger-accepted-ledger-construction
     std::shared_ptr<AcceptedLedger> alpAccepted =
         app_.getAcceptedLedgerCache().fetch(lpAccepted->info().hash);
     if (!alpAccepted)
@@ -2901,6 +2927,7 @@ NetworkOPsImp::pubLedger(std::shared_ptr<ReadView const> const& lpAccepted)
         app_.getAcceptedLedgerCache().canonicalize_replace_client(
             lpAccepted->info().hash, alpAccepted);
     }
+    //@@end pubLedger-accepted-ledger-construction
 
     XRPL_ASSERT(
         alpAccepted->getLedger().get() == lpAccepted.get(),