diff --git a/.gitmodules b/.gitmodules
index 2833d4664..3fae692ed 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -4,3 +4,19 @@
 [submodule "vendor/elm-format"]
 	path = vendor/elm-format
 	url = git@github.com:lamdera/elm-format.git
+[submodule "extra/package-replacements/elm/virtual-dom"]
+	path = extra/package-replacements/elm/virtual-dom
+	url = git@github.com:lydell/virtual-dom.git
+	branch = hot-reload-stop
+[submodule "extra/package-replacements/elm/browser"]
+	path = extra/package-replacements/elm/browser
+	url = git@github.com:lydell/browser.git
+	branch = lamdera
+[submodule "extra/package-replacements/elm/html"]
+	path = extra/package-replacements/elm/html
+	url = git@github.com:lydell/html.git
+	branch = safe
+[submodule "extra/package-replacements/elm/core"]
+	path = extra/package-replacements/elm/core
+	url = git@github.com:lydell/core.git
+	branch = lamdera
diff --git a/builder/src/Elm/Details.hs b/builder/src/Elm/Details.hs
index 29af1b519..4958697f9 100644
--- a/builder/src/Elm/Details.hs
+++ b/builder/src/Elm/Details.hs
@@ -63,6 +63,8 @@ import qualified Stuff
 import qualified Lamdera
 import Lamdera ((&))
 import qualified Lamdera.Extensions
+import qualified Lamdera.PackageReplacements
+import qualified Lamdera.Version
 
 -- DETAILS
 
@@ -405,7 +407,7 @@ verifyDep (Env key _ _ cache manager _ _) depsMVar solution pkg details@(Solver.
         then
           do  Reporting.report key Reporting.DCached
               maybeCache <- File.readBinary (Stuff.package cache pkg vsn </> "artifacts.dat")
-                              & Lamdera.alternativeImplementation (File.readBinary (Stuff.package cache pkg vsn </> "artifacts.x.dat"))
+                              & Lamdera.alternativeImplementation (File.readBinary (Stuff.package cache pkg vsn </> Lamdera.Version.artifacts))
               case maybeCache of
                 Nothing ->
                   build key cache depsMVar pkg details fingerprint Set.empty
@@ -500,7 +502,7 @@ build key cache depsMVar pkg (Solver.Details vsn _) f fs =
                                 Just results ->
                                   let
                                     path = Stuff.package cache pkg vsn </> "artifacts.dat"
-                                             & Lamdera.alternativeImplementation (Stuff.package cache pkg vsn </> "artifacts.x.dat")
+                                             & Lamdera.alternativeImplementation (Stuff.package cache pkg vsn </> Lamdera.Version.artifacts)
                                     ifaces = gatherInterfaces exposedDict results
                                     objects = gatherObjects results
                                     artifacts = Artifacts ifaces objects
@@ -622,6 +624,7 @@ crawlModule foreignDeps mvar pkg src docsStatus name =
 crawlFile :: Map.Map ModuleName.Raw ForeignInterface -> MVar StatusDict -> Pkg.Name -> FilePath -> DocsStatus -> ModuleName.Raw -> FilePath -> IO (Maybe Status)
 crawlFile foreignDeps mvar pkg src docsStatus expectedName path =
   do  bytes <- File.readUtf8 path
+               & Lamdera.alternativeImplementationPassthrough (Lamdera.PackageReplacements.get pkg expectedName Lamdera.PackageReplacements.elm)
       case Parse.fromByteString (Parse.Package pkg) bytes of
         Right modul@(Src.Module (Just (A.At _ actualName)) _ _ imports _ _ _ _ _) | expectedName == actualName ->
           do  deps <- crawlImports foreignDeps mvar pkg src imports
@@ -649,6 +652,7 @@ crawlKernel foreignDeps mvar pkg src name =
       if exists
         then
           do  bytes <- File.readUtf8 path
+                       & Lamdera.alternativeImplementationPassthrough (Lamdera.PackageReplacements.get pkg name Lamdera.PackageReplacements.kernel)
               case Kernel.fromByteString pkg (Map.mapMaybe getDepHome foreignDeps) bytes of
                 Nothing ->
                   return Nothing
diff --git a/builder/src/Stuff.hs b/builder/src/Stuff.hs
index 6d3f56568..62a05bbd9 100644
--- a/builder/src/Stuff.hs
+++ b/builder/src/Stuff.hs
@@ -36,6 +36,7 @@ import qualified Elm.Version as V
 
 import Lamdera ((&))
 import qualified Lamdera
+import qualified Lamdera.Version
 
 -- PATHS
 
@@ -43,6 +44,7 @@ import qualified Lamdera
 stuff :: FilePath -> FilePath
 stuff root =
   root </> "elm-stuff" </> compilerVersion
+  & Lamdera.alternativeImplementation (root </> "elm-stuff" </> Lamdera.Version.medium)
 
 
 details :: FilePath -> FilePath
diff --git a/compiler/src/Generate/Html.hs b/compiler/src/Generate/Html.hs
index b572d0509..875371d15 100644
--- a/compiler/src/Generate/Html.hs
+++ b/compiler/src/Generate/Html.hs
@@ -84,7 +84,7 @@ sandwich_ root moduleName javascript =
 
 <body>
 
-<pre id="elm"></pre>
+<pre data-elm id="elm"></pre>
 
 <script>
 try {
diff --git a/extra/Lamdera/CLI/Reset.hs b/extra/Lamdera/CLI/Reset.hs
index 306127253..a325476c1 100644
--- a/extra/Lamdera/CLI/Reset.hs
+++ b/extra/Lamdera/CLI/Reset.hs
@@ -58,8 +58,7 @@ run () () = do
           progress $ "Removing artifacts in " <> elmHome
           let packageDir = elmHome </> Lamdera.Version.elm </> "packages"
           onlyWhen_ (doesDirectoryExist packageDir) $ do
-            callCommand $ "find " <> packageDir <> " | grep artifacts.dat | xargs rm -r"
-            callCommand $ "find " <> packageDir <> " | grep artifacts.x.dat | xargs rm -r"
+            callCommand $ "find " <> packageDir <> " | grep 'artifacts.*\\.dat' | xargs rm -r"
         else do
           nukeDir elmHome
 
diff --git a/extra/Lamdera/Evergreen/Snapshot.hs b/extra/Lamdera/Evergreen/Snapshot.hs
index 0c54d98f9..312fd79f6 100644
--- a/extra/Lamdera/Evergreen/Snapshot.hs
+++ b/extra/Lamdera/Evergreen/Snapshot.hs
@@ -648,6 +648,7 @@ canonicalToFt version scope interfaces recursionSet canonical tvarMap =
 
 
         -- Kernel concessions for Frontend Model and Msg
+        ("elm", "browser", "Browser.Navigation", "Key") -> ("Browser.Navigation.Key", Set.singleton moduleName, Map.empty)
         ("elm", "file", "File", "File") -> ("File.File", Set.singleton moduleName, Map.empty)
         ("elm-explorations", "webgl", "WebGL.Texture", "Texture") -> ("WebGL.Texture.Texture", Set.singleton moduleName, Map.empty)
 
diff --git a/extra/Lamdera/Injection.hs b/extra/Lamdera/Injection.hs
index a90842910..b86a51b49 100644
--- a/extra/Lamdera/Injection.hs
+++ b/extra/Lamdera/Injection.hs
@@ -171,564 +171,81 @@ source mode mains =
 
 injections :: OutputType -> Mode.Mode -> Text
 injections outputType mode =
-  let
-    previousVersionInt =
-      -- @TODO maybe its time to consolidate the global config...
-      (unsafePerformIO $ lookupEnv "VERSION")
-        & maybe "0" id
-        & read
-        & subtract 1
-
-    previousVersion = show_ previousVersionInt
-
-    {-| This code overrides how == is handled in Elm for SeqDict and SeqSet.
-        The code for handling Dict and Set is also injected here though the behavior is unchanged.
-
-        The entire == function kernel code is overriden further down* and this is inserted into it,
-        but the rest of the equals function kernel code is the same regardless of whether --optimize is used or not so
-        it was cleaner to not write it all twice for --optimize and non--optimize.
-
-        *like with Dict and Set, the rest of the equals kernel code behavior is unchanged.
-     -}
-    equalsOverride =
-        if isOptimizedMode mode then
-         [text|
-              if (x.$$ < 0)
-              {
-                if (x.$$ < -10)
-                {
-                  x = $$lamdera$$containers$$SeqDict$$toList(x);
-                  y = $$lamdera$$containers$$SeqDict$$toList(y);
-                }
-                else
-                {
-                  x = $$elm$$core$$Dict$$toList(x);
-                  y = $$elm$$core$$Dict$$toList(y);
-                }
-              }
-         |]
-       else
-         [text|
-            if (x.$$ === 'Set_elm_builtin')
-            {
-              x = $$elm$$core$$Set$$toList(x);
-              y = $$elm$$core$$Set$$toList(y);
-            }
-            if (x.$$ === 'RBNode_elm_builtin' || x.$$ === 'RBEmpty_elm_builtin')
-            {
-              x = $$elm$$core$$Dict$$toList(x);
-              y = $$elm$$core$$Dict$$toList(y);
-            }
-            if (x.$$ === 'SeqDict_elm_builtin')
-            {
-              x = $$lamdera$$containers$$SeqDict$$toList(x);
-              y = $$lamdera$$containers$$SeqDict$$toList(y);
-            }
-            if (x.$$ === 'SeqSet_elm_builtin')
-            {
-              x = $$lamdera$$containers$$SeqSet$$toList(x);
-              y = $$lamdera$$containers$$SeqSet$$toList(y);
-            }
-         |]
-
-    lamderaContainersExtensions_ =
-      Ext.Common.bsToText lamderaContainersExtensions
-        & Text.replace "// equals override injection marker" equalsOverride
-  in
   case outputType of
-    -- NotLamdera was added when we fixed the hot loading of a new app version in the browser.
-    -- The frontend version of the injections – which used to be what you got when using the
-    -- lamdera compiler for non-lamdera things – then became much more complicated.
-    -- In order not to break elm-pages (which calls `app.die()`) we preserved the old frontend
-    -- injections. Note that the `.die()` method is incomplete: It does not kill all apps completely
-    -- and does not help the garbage collector enough for a killed app to be fully garbage collected.
     NotLamdera ->
       [text|
 
-    $lamderaContainersExtensions_
-
-    function _Platform_initialize(flagDecoder, args, init, update, subscriptions, stepperBuilder)
-      {
-        var result = A2(_Json_run, flagDecoder, _Json_wrap(args ? args['flags'] : undefined));
-
-        // @TODO need to figure out how to get this to automatically escape by mode?
-        //$$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**/, _Json_errorToString(result.a) /**/);
-        $$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**_UNUSED/, _Json_errorToString(result.a) /**/);
-
-        var managers = {};
-        var initPair = init(result.a);
-        var model = (args && args['model']) || initPair.a;
-
-        var stepper = stepperBuilder(sendToApp, model);
-        var ports = _Platform_setupEffects(managers, sendToApp);
-
-        var upgradeMode = false;
-
-        function sendToApp(msg, viewMetadata)
-        {
-          if (upgradeMode) {
-            // No more messages should run in upgrade mode
-            _Platform_enqueueEffects(managers, $$elm$$core$$Platform$$Cmd$$none, $$elm$$core$$Platform$$Sub$$none);
-            return;
-          }
-
-          var pair = A2(update, msg, model);
-          stepper(model = pair.a, viewMetadata);
-          _Platform_enqueueEffects(managers, pair.b, subscriptions(model));
-        }
-
-        if ((args && args['model']) === undefined) {
-          _Platform_enqueueEffects(managers, initPair.b, subscriptions(model));
-        }
-
-        const die = function() {
-          // Stop all subscriptions.
-          // This must be done before clearing the stuff below.
-          _Platform_enqueueEffects(managers, _Platform_batch(_List_Nil), _Platform_batch(_List_Nil));
-
-          managers = null;
-          model = null;
-          stepper = null;
-          ports = null;
-          _Platform_effectsQueue = [];
-        }
-
-        return ports ? {
-          ports: ports,
-          gm: function() { return model },
-          eum: function() { upgradeMode = true },
-          die: die,
-          fns: {}
-        } : {};
-      }
+    function _Lamdera_inject(app) {
+      app.die = app.stop;
+    }
       |]
 
     LamderaBackend ->
       [text|
 
-    $lamderaContainersExtensions_
-
-    function _Platform_initialize(flagDecoder, args, init, update, subscriptions, stepperBuilder)
-      {
-        var result = A2(_Json_run, flagDecoder, _Json_wrap(args ? args['flags'] : undefined));
-
-        // @TODO need to figure out how to get this to automatically escape by mode?
-        //$$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**/, _Json_errorToString(result.a) /**/);
-        $$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**_UNUSED/, _Json_errorToString(result.a) /**/);
-
-        var managers = {};
-        var initPair = init(result.a);
-        var model = (args && args['model']) || initPair.a;
-
-        var stepper = stepperBuilder(sendToApp, model);
-        var ports = _Platform_setupEffects(managers, sendToApp);
-
-        var upgradeMode = false;
-
-        function sendToApp(msg, viewMetadata)
-        {
-          if (upgradeMode) {
-            // No more messages should run in upgrade mode
-            _Platform_enqueueEffects(managers, $$elm$$core$$Platform$$Cmd$$none, $$elm$$core$$Platform$$Sub$$none);
-            return;
-          }
-
-          stepper(model = pair.a, viewMetadata);
-          _Platform_enqueueEffects(managers, pair.b, subscriptions(model));
-        }
-
-        if ((args && args['model']) === undefined) {
-          _Platform_enqueueEffects(managers, initPair.b, subscriptions(model));
-        }
-
-        const die = function() {
-          // Stop all subscriptions.
-          // This must be done before clearing the stuff below.
-          _Platform_enqueueEffects(managers, _Platform_batch(_List_Nil), _Platform_batch(_List_Nil));
-
-          managers = null;
-          model = null;
-          stepper = null;
-          ports = null;
-          _Platform_effectsQueue = [];
-        }
-
-        return ports ? {
-          ports: ports,
-          gm: function() { return model },
-          eum: function() { upgradeMode = true },
-          die: die,
-          fns: {}
-        } : {};
-      }
-
     var isLamderaRuntime = typeof isLamdera !== 'undefined';
 
-    function _Platform_initialize(flagDecoder, args, init, update, subscriptions, stepperBuilder)
-      {
-        var result = A2(_Json_run, flagDecoder, _Json_wrap(args ? args['flags'] : undefined));
-
-        // @TODO need to figure out how to get this to automatically escape by mode?
-        //$$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**/, _Json_errorToString(result.a) /**/);
-        $$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**_UNUSED/, _Json_errorToString(result.a) /**/);
-
-
-        var managers = {};
-        var initPair = init(result.a);
-        var model = (args && args['model']) || initPair.a;
+    function _Lamdera_inject(app, callUpdate, model) {
+      app.die = app.stop;
 
-        var stepper = stepperBuilder(sendToApp, model);
-        var ports = _Platform_setupEffects(managers, sendToApp);
+      app.fns =
+        { decodeWirePayloadHeader: $$author$$project$$LamderaHelpers$$decodeWirePayloadHeader
+        , decodeWireAnalytics: $$author$$project$$LamderaHelpers$$decodeWireAnalytics
+        , getUserModel : function() { return model.userModel }
+        };
 
-        var pos = 0;
+      var pos = 0;
 
-        function mtime() { // microseconds
-          if (!isLamderaRuntime) { return 0; }
-          const hrTime = process.hrtime();
-          return Math.floor(hrTime[0] * 1000000 + hrTime[1] / 1000);
-        }
+      function mtime() { // microseconds
+        if (!isLamderaRuntime) { return 0; }
+        const hrTime = process.hrtime();
+        return Math.floor(hrTime[0] * 1000000 + hrTime[1] / 1000);
+      }
 
-        var buriedTimestamp = null;
+      callUpdate.call = function(update, msg, model) {
+        var serializeDuration, logDuration = null;
+        var start = mtime();
 
-        function sendToApp(msg, viewMetadata)
-        {
-          if (buriedTimestamp !== null) {
-            const elapsed = Date.now() - buriedTimestamp;
-            // This tries to turn `HomePageMsg (WeatherWidgetMsg (WeatherReportReceived WeatherReport))`
-            // into `"HomePageMsg WeatherWidgetMsg WeatherReportReceived"`.
-            // The idea is that if the timeout for forwarding messages isn't enough, we want to know what
-            // message somebody used that took even longer, but without reporting the entire msg.
-            // Note that in `--optimize` mode, the above string would become something like `"1 3 6"`,
-            // but it's better than nothing.
-            let msgName = '(unknown message)';
-            if (msg.$) {
-              msgName = msg.$;
-              let current = msg;
-              while (current.a && current.a.$ && !current.b) {
-                current = current.a;
-                msgName = msgName + ' ' + current.$;
-              }
-            }
-            bugsnag.notify(new Error('Got message ' + elapsed + ' ms after app was buried: ' + msgName));
-            return;
-          }
-
-          var serializeDuration, logDuration = null;
-          var start = mtime();
+        var pair = A2(update, msg, model);
 
-          var pair = A2(update, msg, model);
+        const updateDuration = mtime() - start;
+        start = mtime();
 
-          const updateDuration = mtime() - start;
+        if (isLamderaRuntime && loggingEnabled) {
+          pos = pos + 1;
+          const s = $$author$$project$$LBR$$serialize(msg);
+          serializeDuration = mtime() - start;
           start = mtime();
-
-          if (isLamderaRuntime && loggingEnabled) {
-            pos = pos + 1;
-            const s = $$author$$project$$LBR$$serialize(msg);
-            serializeDuration = mtime() - start;
-            start = mtime();
-            insertEvent(pos, global.config.version, s.a, updateDuration, serializeDuration, A2($$elm$$core$$Maybe$$withDefault, null, s.b));
-            logDuration = mtime() - start;
-          }
-
-          stepper(model = pair.a, viewMetadata);
-          _Platform_enqueueEffects(managers, pair.b, subscriptions(model));
-        }
-
-        if ((args && args['model']) === undefined) {
-          _Platform_enqueueEffects(managers, initPair.b, subscriptions(model));
-        }
-
-        var fns =
-          { decodeWirePayloadHeader: $$author$$project$$LamderaHelpers$$decodeWirePayloadHeader
-          , decodeWireAnalytics: $$author$$project$$LamderaHelpers$$decodeWireAnalytics
-          , getUserModel : function() { return model.userModel }
-          }
-
-        const die = function() {
-          // In case there still are any pending commands, setting this flag means
-          // that nothing happens when they finish.
-          buriedTimestamp = Date.now();
-
-          // The app won't be garbage collected until all pending commands are done.
-          // We can reclaim most memory immediately by manually clearing the model early.
-          model = null;
-
-          // On the frontend, we have to clear the effect managers, since they prevent sendToApp from being GC:ed,
-          // which prevents the whole app from being GC:ed. On the backend, it does not seem to.
-          // We still do it here for consistency (it doesn't hurt).
-          _Platform_effectManagers = {};
+          insertEvent(pos, global.config.version, s.a, updateDuration, serializeDuration, A2($$elm$$core$$Maybe$$withDefault, null, s.b));
+          logDuration = mtime() - start;
         }
 
-        // On the frontend, clearing args helps garbage collection. On the backend, it does not seem to.
-        // We still do it here for consistency (it doesn't hurt).
-        args = null;
-
-        return ports ? {
-          ports: ports,
-          die: die,
-          fns: fns
-        } : {};
-      }
+        model = pair.a;
+        return pair;
+      };
+    }
       |]
 
-    -- LamderaFrontend or LamderaLive
-    _ ->
-      let
-        shouldProxy =
-          onlyIf (outputType == LamderaLive)
-            [text|
-              shouldProxy = $$author$$project$$Lamdera$$Live$$shouldProxy(msg)
-            |]
-      in
+    LamderaFrontend ->
       [text|
 
-    $lamderaContainersExtensions_
-
-    function _Platform_initialize(flagDecoder, args, init, update, subscriptions, stepperBuilder)
-      {
-        var result = A2(_Json_run, flagDecoder, _Json_wrap(args ? args['flags'] : undefined));
-
-        // @TODO need to figure out how to get this to automatically escape by mode?
-        //$$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**/, _Json_errorToString(result.a) /**/);
-        $$elm$$core$$Result$$isOk(result) || _Debug_crash(2 /**_UNUSED/, _Json_errorToString(result.a) /**/);
-
-        var managers = {};
-        var initPair = init(result.a);
-        var model = initPair.a;
-
-        // We'll temporarily overwrite these variables or functions.
-        var F2_backup = F2;
-        var _Browser_window_backup = _Browser_window;
-        var _VirtualDom_virtualize_backup = _VirtualDom_virtualize;
-        var _VirtualDom_applyPatches_backup = _VirtualDom_applyPatches;
-        var _VirtualDom_equalEvents_backup = _VirtualDom_equalEvents;
-
-        // stepperBuilder calls impl.setup() (if it exists, which it does only for
-        // Browser.application) as the first thing it does. impl.setup() returns the
-        // divertHrefToApp function, which is used to create the event listener for
-        // all <a> elements. That divertHrefToApp function is constructed using F2.
-        // Here we override F2 to store the listener on the DOM node so we can
-        // remove it later. _VirtualDom_virtualize is called a couple of lines
-        // later, so we use that to restore the original F2 function, so it can do
-        // the right thing when the view function is called.
-        F2 = function(f) {
-          return function(domNode) {
-            var listener = function(event) {
-              return f(domNode, event);
-            };
-            domNode.elmAf = listener;
-            return listener;
-          };
-        };
-
-        // To get hold of the Browser.Navigation.key, and to be able to remove the popstate and hashchange listeners.
-        _Browser_window = {
-          navigator: _Browser_window_backup.navigator,
-          addEventListener: function(eventName, listener) {
-            _Browser_navKey = listener;
-            _Browser_window_backup.addEventListener(eventName, listener);
-          },
-        };
-
-        // When passing in the last rendered VNode from a previous app:
-        if (args && args.vn) {
-          // Instead of virtualizing the existing DOM into a VNode, just use the
-          // one from the previous app. Html.map messes up Elm's
-          // _VirtualDom_virtualize, causing the entire thing inside the Html.map
-          // to be re-created even though it is already the correct DOM.
-          _VirtualDom_virtualize = function() {
-            F2 = F2_backup; // Restore F2 as mentioned above.
-            return args.vn;
-          };
-
-          _VirtualDom_applyPatches = function(rootDomNode, oldVirtualNode, patches, eventNode) {
-            if (patches.length !== 0) {
-              _VirtualDom_addDomNodes(rootDomNode, oldVirtualNode, patches, eventNode);
-            }
-            _VirtualDom_lastDomNode = _VirtualDom_applyPatchesHelp(rootDomNode, patches);
-            // Restore the event listeners on the <a> elements:
-            var aElements = _VirtualDom_lastDomNode.getElementsByTagName('a');
-            for (var i = 0; i < aElements.length; i++) {
-              var domNode = aElements[i];
-              domNode.addEventListener('click', _VirtualDom_divertHrefToApp(domNode));
-            }
-            return _VirtualDom_lastDomNode;
-          }
-
-          // Force all event listeners to be re-applied:
-          _VirtualDom_equalEvents = function() {
-            return false;
-          }
-        } else {
-          _VirtualDom_virtualize = function(node) {
-            F2 = F2_backup; // Restore F2 as mentioned above.
-            return _VirtualDom_virtualize_backup(node);
-          };
-        }
-
-        var stepper = stepperBuilder(sendToApp, model);
-
-        // Restore the original functions and variables.
-        F2 = F2_backup; // Should already be restored by now, but just in case.
-        _Browser_window = _Browser_window_backup;
-        _VirtualDom_virtualize = _VirtualDom_virtualize_backup;
-        _VirtualDom_applyPatches = _VirtualDom_applyPatches_backup;
-        _VirtualDom_equalEvents = _VirtualDom_equalEvents_backup;
-
-        if (args && args.vn) {
-          // Html.map puts `.elm_event_node_ref = { __tagger: taggers, __parent: parent_elm_event_node_ref }`
-          // on the DOM node for its first non-Html.map child virtual DOM node. __parent is a reference to
-          // the .elm_event_node_ref of a parent Html.map further up the tree. Modifying one modifies the other,
-          // since they are the same object. The top-most Html.map nodes have __parent set to the sendToApp function.
-          // All the __tagger should be updated now to stuff from the new app, but the __parent sendToApp still points
-          // to the old app, so we need to update it to the current app.
-          // This relies on that fact that we do `List.map (Html.map FEMsg) body`. If that weren't the case, we could
-          // have to crawl the tree recursively to find the top-most Html.map nodes.
-          for (var i = 0; i < _VirtualDom_lastDomNode.childNodes.length; i++) {
-            var element = _VirtualDom_lastDomNode.childNodes[i];
-            if (element.elm_event_node_ref && typeof element.elm_event_node_ref.p === 'function') {
-              element.elm_event_node_ref.p = sendToApp;
-            }
-          }
-        }
-
-        var ports = _Platform_setupEffects(managers, sendToApp);
-
-        var buriedTimestamp = null;
-
-        function sendToApp(msg, viewMetadata)
-        {
-          if (buriedTimestamp !== null) {
-            const elapsed = Date.now() - buriedTimestamp;
-            let msgName = '(unknown message)';
-            if (msg.$) {
-              msgName = msg.$;
-              let current = msg;
-              while (current.a && current.a.$ && !current.b) {
-                current = current.a;
-                msgName = msgName + ' ' + current.$;
-              }
-            }
-            window.lamdera.bs.notify(new Error('Got message ' + elapsed + ' ms after app was buried: ' + msgName));
-            return;
-          }
-
-          $shouldProxy
-
-          var pair = A2(update, msg, model);
-          stepper(model = pair.a, viewMetadata);
-          _Platform_enqueueEffects(managers, pair.b, subscriptions(model));
-        }
-
-        _Platform_enqueueEffects(managers, initPair.b, subscriptions(model));
-
-        // Stops the app from getting more input, and from rendering.
-        // It doesn't die completely: Already running cmds will still run, and
-        // hit the update function, which then redirects the messages to the new app.
-        const die = function() {
-          // Render one last time, synchronously, in case there is a scheduled
-          // render with requestAnimationFrame (which then become no-ops).
-          // Rendering mutates the vdom, and we want those mutations.
-          stepper(model, true /* isSync */);
-
-          // Remove Elm's event listeners. Both the ones added
-          // automatically on every <a> element, as well as the ones
-          // added by using Html.Events.
-          var elements = _VirtualDom_lastDomNode.getElementsByTagName('*');
-          for (var i = 0; i < elements.length; i++) {
-            var element = elements[i];
-            if (element.elmAf) {
-              element.removeEventListener('click', element.elmAf);
-              delete element.elmAf;
-            }
-            if (element.elmFs) {
-              for (var key in element.elmFs) {
-                element.removeEventListener(key, element.elmFs[key]);
-              }
-              delete element.elmFs;
-            }
-            // Leave element.elm_event_node_ref behind, because the first
-            // render in the new app crashes otherwise. It contains references
-            // to the old app, but all of that should go away after the first
-            // render, and the element.elm_event_node_ref.p stuff above.
-          }
-
-          // Remove the popstate and hashchange listeners.
-          if (_Browser_navKey) {
-            _Browser_window.removeEventListener('popstate', _Browser_navKey);
-            _Browser_window.removeEventListener('hashchange', _Browser_navKey);
-            // Remove reference to .a aka .__sendToApp which prevents GC.
-            delete _Browser_navKey.a;
-          }
-
-          // Stop rendering:
-          stepper = function() {};
-
-          // Note that subscriptions are turned off in Elm (by returning Sub.none)
-          // in upgrade mode, and the update function stops doing its regular business
-          // and just forwards messages instead.
-
-          return _VirtualDom_lastVNode;
-        }
-
-        // This can't be done in the die function, because then it's not possible to
-        // trigger an outgoing port to redirect messages. This is supposed to be called
-        // when all pending commands are done.
-        const bury = function() {
-          // In case there still are any pending commands, setting this flag means
-          // that nothing happens when they finish.
-          buriedTimestamp = Date.now();
-
-          // The app won't be garbage collected until all pending commands are done.
-          // We can reclaim most memory immediately by manually clearing the model early.
-          model = null;
-
-          // Clear effect managers, since they prevent sendToApp from being GC:ed,
-          // which prevents the whole app from being GC:ed.
-          _Platform_effectManagers = {};
-        };
-
-        // Clearing args means the flags (like the passed in model) can be GC:ed (in the new app).
-        args = null;
-
-        return ports ? {
-          ports: ports,
-          die: die,
-          bury: bury,
-        } : {};
-      }
-
-    // Keep track of the last VNode rendered so we can pass it to the next app later.
-    var _VirtualDom_lastVNode = null;
-    function _VirtualDom_diff(x, y)
-    {
-      _VirtualDom_lastVNode = y;
-      var patches = [];
-      _VirtualDom_diffHelp(x, y, patches, 0);
-      return patches;
-    }
-
-    // Keep track of the reference to the latest root DOM node so we can perform cleanups in it later.
-    var _VirtualDom_lastDomNode = null;
-    function _VirtualDom_applyPatches(rootDomNode, oldVirtualNode, patches, eventNode)
-    {
-      if (patches.length === 0)
-      {
-        return (_VirtualDom_lastDomNode = rootDomNode);
-      }
-
-      _VirtualDom_addDomNodes(rootDomNode, oldVirtualNode, patches, eventNode);
-      return (_VirtualDom_lastDomNode = _VirtualDom_applyPatchesHelp(rootDomNode, patches));
+    function _Lamdera_inject(app) {
+      app.die = app.stop;
     }
 
     // In Elm, Browser.Navigation.Key is a function behind the scenes. It is passed and called here.
     // In Lamdera, the Key becomes an object after a Wire roundtrip, so we just take the key as a "password"
-    // but then call the actual function ourselves.
-    var _Browser_navKey = null;
+    // but then call the actual function ourselves. We _could_ Wire it as a reference, but then we have a
+    // new problem: The key function is from the _old_ app and references functions and data from the old app.
+    // So we would need to be able to update it, both so that it works and to not leak memory from the old app.
+    // That could be doable by introducing a special reference Wire encoding specifically for Browser.Navigation.Key.
+    // But even if we do that we still have a problem: Migrating from apps that doesn't have that new Wire encoding yet.
+    // As long as we want to support migrating such apps, we have to stay with the solution below.
+    var _Lamdera_navKey = function() {};
     var _Browser_go = F2(function(key, n) {
       return A2($$elm$$core$$Task$$perform, $$elm$$core$$Basics$$never, _Scheduler_binding(function() {
         n && history.go(n);
-        _Browser_navKey();
+        _Lamdera_navKey();
       }));
     });
     // $$elm$$browser$$Browser$$Navigation$$back is not a direct assignment so it does not need to be replaced.
@@ -736,19 +253,32 @@ injections outputType mode =
     var _Browser_pushUrl = F2(function(key, url) {
       return A2($$elm$$core$$Task$$perform, $$elm$$core$$Basics$$never, _Scheduler_binding(function() {
         history.pushState({}, "", url);
-        _Browser_navKey();
+        _Lamdera_navKey();
       }));
     });
     var $$elm$$browser$$Browser$$Navigation$$pushUrl = _Browser_pushUrl;
     var _Browser_replaceUrl = F2(function(key, url) {
       return A2($$elm$$core$$Task$$perform, $$elm$$core$$Basics$$never, _Scheduler_binding(function() {
         history.replaceState({}, "", url);
-        _Browser_navKey();
+        _Lamdera_navKey();
       }));
     });
     var $$elm$$browser$$Browser$$Navigation$$replaceUrl = _Browser_replaceUrl;
       |]
 
+    LamderaLive ->
+      [text|
+
+    function _Lamdera_inject(app, callUpdate) {
+      app.die = app.stop;
+
+      callUpdate.call = function(update, msg, model) {
+        shouldProxy = $$author$$project$$Lamdera$$Live$$shouldProxy(msg);
+        return A2(update, msg, model);
+      };
+    }
+      |]
+
   --   // https://github.com/elm/bytes/issues/20
   --   // but the fix below as suggested causes this problem:
   --   // https://github.com/nodejs/node/issues/26115
@@ -927,14 +457,3 @@ mainsInclude list mains =
         else False
     _ ->
       False
-
-{-|
-  Overrides to the following functions to add support for lamdera/containers SeqDict and SeqSet,
-  displaying as `SeqDict.fromList [ ... ]` and `SeqSet.fromList [ ... ]`
-
-  _Debug_toAnsiString
-  _Utils_eqHelp
--}
-lamderaContainersExtensions :: BS.ByteString
-lamderaContainersExtensions =
-  $(bsToExp =<< runIO (Lamdera.Relative.readByteString "extra/Lamdera/Injection/lamdera-containers-extensions.js"))
diff --git a/extra/Lamdera/Injection/lamdera-containers-extensions.js b/extra/Lamdera/Injection/lamdera-containers-extensions.js
deleted file mode 100644
index d3039ffd3..000000000
--- a/extra/Lamdera/Injection/lamdera-containers-extensions.js
+++ /dev/null
@@ -1,185 +0,0 @@
-function _Debug_toAnsiString(ansi, value)
-{
-  if (typeof value === 'function')
-  {
-    return _Debug_internalColor(ansi, '<function>');
-  }
-
-  if (typeof value === 'boolean')
-  {
-    return _Debug_ctorColor(ansi, value ? 'True' : 'False');
-  }
-
-  if (typeof value === 'number')
-  {
-    return _Debug_numberColor(ansi, value + '');
-  }
-
-  if (value instanceof String)
-  {
-    return _Debug_charColor(ansi, "'" + _Debug_addSlashes(value, true) + "'");
-  }
-
-  if (typeof value === 'string')
-  {
-    return _Debug_stringColor(ansi, '"' + _Debug_addSlashes(value, false) + '"');
-  }
-
-  if (typeof value === 'object' && '$' in value)
-  {
-    var tag = value.$;
-
-    if (typeof tag === 'number')
-    {
-      return _Debug_internalColor(ansi, '<internals>');
-    }
-
-    if (tag[0] === '#')
-    {
-      var output = [];
-      for (var k in value)
-      {
-        if (k === '$') continue;
-        output.push(_Debug_toAnsiString(ansi, value[k]));
-      }
-      return '(' + output.join(',') + ')';
-    }
-
-    if (tag === 'Set_elm_builtin')
-    {
-      return _Debug_ctorColor(ansi, 'Set')
-        + _Debug_fadeColor(ansi, '.fromList') + ' '
-        + _Debug_toAnsiString(ansi, $elm$core$Set$toList(value));
-    }
-
-    if (tag === 'RBNode_elm_builtin' || tag === 'RBEmpty_elm_builtin')
-    {
-      return _Debug_ctorColor(ansi, 'Dict')
-        + _Debug_fadeColor(ansi, '.fromList') + ' '
-        + _Debug_toAnsiString(ansi, $elm$core$Dict$toList(value));
-    }
-
-    if (tag === 'SeqSet_elm_builtin')
-    {
-      return _Debug_ctorColor(ansi, 'SeqSet')
-        + _Debug_fadeColor(ansi, '.fromList') + ' '
-        + _Debug_toAnsiString(ansi, $lamdera$containers$SeqSet$toList(value));
-    }
-
-    if (tag === 'SeqDict_elm_builtin')
-    {
-      return _Debug_ctorColor(ansi, 'SeqDict')
-        + _Debug_fadeColor(ansi, '.fromList') + ' '
-        + _Debug_toAnsiString(ansi, $lamdera$containers$SeqDict$toList(value));
-    }
-
-    if (tag === 'Array_elm_builtin')
-    {
-      return _Debug_ctorColor(ansi, 'Array')
-        + _Debug_fadeColor(ansi, '.fromList') + ' '
-        + _Debug_toAnsiString(ansi, $elm$core$Array$toList(value));
-    }
-
-    if (tag === '::' || tag === '[]')
-    {
-      var output = '[';
-
-      value.b && (output += _Debug_toAnsiString(ansi, value.a), value = value.b)
-
-      for (; value.b; value = value.b) // WHILE_CONS
-      {
-        output += ',' + _Debug_toAnsiString(ansi, value.a);
-      }
-      return output + ']';
-    }
-
-    var output = '';
-    for (var i in value)
-    {
-      if (i === '$') continue;
-      var str = _Debug_toAnsiString(ansi, value[i]);
-      var c0 = str[0];
-      var parenless = c0 === '{' || c0 === '(' || c0 === '[' || c0 === '<' || c0 === '"' || str.indexOf(' ') < 0;
-      output += ' ' + (parenless ? str : '(' + str + ')');
-    }
-    return _Debug_ctorColor(ansi, tag) + output;
-  }
-
-  if (typeof DataView === 'function' && value instanceof DataView)
-  {
-    return _Debug_stringColor(ansi, '<' + value.byteLength + ' bytes>');
-  }
-
-  if (typeof File !== 'undefined' && value instanceof File)
-  {
-    return _Debug_internalColor(ansi, '<' + value.name + '>');
-  }
-
-  if (typeof value === 'object')
-  {
-    var output = [];
-    for (var key in value)
-    {
-      var field = key[0] === '_' ? key.slice(1) : key;
-      output.push(_Debug_fadeColor(ansi, field) + ' = ' + _Debug_toAnsiString(ansi, value[key]));
-    }
-    if (output.length === 0)
-    {
-      return '{}';
-    }
-    return '{ ' + output.join(', ') + ' }';
-  }
-
-  return _Debug_internalColor(ansi, '<internals>');
-}
-
-function _Debug_addSlashes(str, isChar)
-{
-  var s = str
-    .replace(/\\/g, '\\\\')
-    .replace(/\n/g, '\\n')
-    .replace(/\t/g, '\\t')
-    .replace(/\r/g, '\\r')
-    .replace(/\v/g, '\\v')
-    .replace(/\0/g, '\\0');
-
-  if (isChar)
-  {
-    return s.replace(/\'/g, '\\\'');
-  }
-  else
-  {
-    return s.replace(/\"/g, '\\"');
-  }
-}
-
-function _Utils_eqHelp(x, y, depth, stack)
-{
-  if (x === y)
-  {
-    return true;
-  }
-
-  if (typeof x !== 'object' || x === null || y === null)
-  {
-    typeof x === 'function' && $elm$core$Debug$crash(5);
-    return false;
-  }
-
-  if (depth > 100)
-  {
-    stack.push(_Utils_Tuple2(x,y));
-    return true;
-  }
-
-  // equals override injection marker
-
-  for (var key in x)
-  {
-    if (!_Utils_eqHelp(x[key], y[key], depth + 1, stack))
-    {
-      return false;
-    }
-  }
-  return true;
-}
diff --git a/extra/Lamdera/PackageReplacements.hs b/extra/Lamdera/PackageReplacements.hs
new file mode 100644
index 000000000..647e8a4f9
--- /dev/null
+++ b/extra/Lamdera/PackageReplacements.hs
@@ -0,0 +1,33 @@
+{-# LANGUAGE TemplateHaskell #-}
+
+module Lamdera.PackageReplacements where
+
+import qualified Data.Map as Map
+import qualified Elm.ModuleName as ModuleName
+import qualified Elm.Package as Pkg
+import Data.ByteString
+
+
+type ReplacementMap = Map.Map ( Pkg.Name, ModuleName.Raw ) ByteString
+
+
+elm :: ReplacementMap
+elm =
+  -- TODO: Use TemplateHaskell to populate this map from extra/package-replacements/*
+  -- Use `git diff master... --name-only` to know which files need to be included
+  Map.empty
+
+
+kernel :: ReplacementMap
+kernel =
+  -- TODO: Same here.
+  Map.empty
+
+
+get :: Pkg.Name -> ModuleName.Raw -> ReplacementMap -> IO ByteString -> IO ByteString
+get pkg name replacementMap original =
+  maybe original return (Map.lookup (pkg, name) replacementMap)
+
+
+-- TODO: Also generate a map of package names and package versions used to validate that the
+-- user elm.json is compatible with our package replacements.
diff --git a/extra/Lamdera/TypeHash.hs b/extra/Lamdera/TypeHash.hs
index a29f0023e..f1cd0327c 100644
--- a/extra/Lamdera/TypeHash.hs
+++ b/extra/Lamdera/TypeHash.hs
@@ -388,6 +388,12 @@ canonicalToDiffableType targetName interfaces recursionSet canonical tvarMap =
 
 
         -- Frontend JS Kernel types
+        ("elm", "browser", "Browser.Navigation", "Key") ->
+          if targetName `elem` ["FrontendMsg", "FrontendModel"] then
+            DKernelBrowser "Browser.Navigation.Key"
+          else
+            kernelErrorBrowserOnly
+
         ("elm", "file", "File", "File") ->
           if targetName `elem` ["FrontendMsg", "FrontendModel"] then
             DKernelBrowser "File.File"
diff --git a/extra/Lamdera/Version.hs b/extra/Lamdera/Version.hs
index dd6a0af33..bda62bd5a 100644
--- a/extra/Lamdera/Version.hs
+++ b/extra/Lamdera/Version.hs
@@ -23,6 +23,10 @@ short :: String
 short = rawToString raw
 
 
+medium :: String
+medium = "lamdera-" <> short <> "-" <> elm
+
+
 full :: String
 full =
   let
@@ -31,7 +35,7 @@ full =
           | otherwise  = ""
   in
   concat
-    [ "lamdera-", short, "-", elm, "-", Ext.Common.os, "-", Ext.Common.arch, "-", giHash gi, dirty
+    [ medium, "-", Ext.Common.os, "-", Ext.Common.arch, "-", giHash gi, dirty
     , " (", giCommitDate gi, ")"
     , " (branch:", giBranch gi, ")"
     ]
@@ -40,3 +44,8 @@ full =
 elm :: String
 elm =
   V.toChars V.compiler
+
+
+artifacts :: String
+artifacts =
+  "artifacts." <> medium <> ".dat"
diff --git a/extra/Lamdera/Wire3/Decoder.hs b/extra/Lamdera/Wire3/Decoder.hs
index b7d056b75..2af46d365 100644
--- a/extra/Lamdera/Wire3/Decoder.hs
+++ b/extra/Lamdera/Wire3/Decoder.hs
@@ -349,6 +349,8 @@ decoderForType ifaces cname tipe =
 
 
     -- Frontend only JS reference types
+    -- See Injection.hs for why we don’t decode `Browser.Navigation.Key` as a reference.
+    -- TType (Module.Canonical (Name "elm" "browser") "Browser.Navigation") "Key" params -> callDecoder "decodeRef" tipe
     TType (Module.Canonical (Name "elm" "file") "File") "File" params -> callDecoder "decodeRef" tipe
     TType (Module.Canonical (Name "elm-explorations" "webgl") "WebGL.Texture") "Texture" params -> callDecoder "decodeRef" tipe
 
@@ -456,4 +458,4 @@ decodeRecord ifaces cname fields =
                     decoderForType ifaces cname field
                 )
           ) fields
-    & foldlPairs (|>)
\ No newline at end of file
+    & foldlPairs (|>)
diff --git a/extra/Lamdera/Wire3/Encoder.hs b/extra/Lamdera/Wire3/Encoder.hs
index 8786f4bc8..c7bb19203 100644
--- a/extra/Lamdera/Wire3/Encoder.hs
+++ b/extra/Lamdera/Wire3/Encoder.hs
@@ -212,6 +212,9 @@ encoderForType depth ifaces cname tipe =
 
 
     -- Frontend only JS reference types
+    -- See Injection.hs for why we don’t encode `Browser.Navigation.Key` as a reference.
+    -- TType (Module.Canonical (Name "elm" "browser") "Browser.Navigation") "Key" _ ->
+    --   (a (VarForeign mLamdera_Wire "encodeRef" (Forall Map.empty (TLambda tipe tLamdera_Wire_Encoder))))
     TType (Module.Canonical (Name "elm" "file") "File") "File" _ ->
       (a (VarForeign mLamdera_Wire "encodeRef" (Forall Map.empty (TLambda tipe tLamdera_Wire_Encoder))))
     TType (Module.Canonical (Name "elm-explorations" "webgl") "WebGL.Texture") "Texture" _ ->
diff --git a/extra/Lamdera/Wire3/Helpers.hs b/extra/Lamdera/Wire3/Helpers.hs
index 471143aa2..a1b822c85 100644
--- a/extra/Lamdera/Wire3/Helpers.hs
+++ b/extra/Lamdera/Wire3/Helpers.hs
@@ -122,6 +122,8 @@ isUnsupportedKernelType tipe =
 
     -- JS types we are supporting through JS ref encodings. These serialisations
     -- CANNOT BE DECODED OUTSIDE OF THE JS SCOPE THEY WERE ENCODED IN!
+    -- See Injection.hs for why we don’t encode `Browser.Navigation.Key` as a reference.
+    -- TType (Module.Canonical (Name "elm" "browser") "Browser.Navigation") "File" _ -> False
     TType (Module.Canonical (Name "elm" "file") "File") "File" _ -> False
     TType (Module.Canonical (Name "elm-explorations" "webgl") "WebGL.Texture") "Texture" _ -> False
 
diff --git a/extra/package-replacements/elm/browser b/extra/package-replacements/elm/browser
new file mode 160000
index 000000000..0af2d19c2
--- /dev/null
+++ b/extra/package-replacements/elm/browser
@@ -0,0 +1 @@
+Subproject commit 0af2d19c2e67f31043522ec683c320a6be10b5fc
diff --git a/extra/package-replacements/elm/core b/extra/package-replacements/elm/core
new file mode 160000
index 000000000..9079a0a41
--- /dev/null
+++ b/extra/package-replacements/elm/core
@@ -0,0 +1 @@
+Subproject commit 9079a0a418722773958e23dcf13db9a9a0516dad
diff --git a/extra/package-replacements/elm/html b/extra/package-replacements/elm/html
new file mode 160000
index 000000000..b35c476a6
--- /dev/null
+++ b/extra/package-replacements/elm/html
@@ -0,0 +1 @@
+Subproject commit b35c476a69f0ba9bf8282d8c15df65e63aefea8f
diff --git a/extra/package-replacements/elm/virtual-dom b/extra/package-replacements/elm/virtual-dom
new file mode 160000
index 000000000..c46dd44dd
--- /dev/null
+++ b/extra/package-replacements/elm/virtual-dom
@@ -0,0 +1 @@
+Subproject commit c46dd44dd0160c0fa61a3e521b4d975e1a0da6b6