Fix out of order state update messages (#3010)

frontend/components/Editor.js

@@ -788,13 +788,23 @@ all patches: ${JSON.stringify(patches, null, 1)}
 
         this.apply_notebook_patches = apply_notebook_patches
         // these are update message that are _not_ a response to a `send(*, *, {create_promise: true})`
+        this.last_update_counter = -1
+        const check_update_counter = (new_val) => {
+            if (new_val <= this.last_update_counter) {
+                console.error("State update out of order", new_val, this.last_update_counter)
+                alert("Oopsie!! please refresh your browser and everything will be alright!")
+            }
+            this.last_update_counter = new_val
+        }
+
         const on_update = (update, by_me) => {
             if (this.state.notebook.notebook_id === update.notebook_id) {
                 const show_debugs = launch_params.binder_url != null
                 if (show_debugs) console.debug("on_update", update, by_me)
                 const message = update.message
                 switch (update.type) {
                     case "notebook_diff":
+                        check_update_counter(message?.counter)
                         let apply_promise = Promise.resolve()
                         if (message?.response?.from_reset) {
                             console.log("Trying to reset state after failure")

src/webserver/Dynamic.jl

@@ -165,6 +165,10 @@ const current_state_for_clients = WeakKeyDict{ClientSession,Any}()
 const current_state_for_clients_lock = ReentrantLock()
 const update_counter_for_debugging = Ref(0)
 
+const update_counter_for_clients_1 = WeakKeyDict{ClientSession,Any}()
+const update_counter_for_clients_2 = WeakKeyDict{ClientSession,Any}()
+const update_counter_for_clients_3 = WeakKeyDict{ClientSession,Any}()
+
 """
 Update the local state of all clients connected to this notebook.
 """
@@ -195,12 +199,12 @@ function send_notebook_changes!(🙋::ClientRequest; commentary::Any=nothing)
                 end
             end
         end
-    end
 
-    for (client, msg) in outbox
-        putclientupdates!(client, msg)
+        for (client, msg) in outbox
+            putclientupdates!(client, msg)
+        end
+        try_event_call(🙋.session, FileEditEvent(🙋.notebook))
     end
-    try_event_call(🙋.session, FileEditEvent(🙋.notebook))
 end
 
 "Like `deepcopy`, but anything other than `Dict` gets a shallow (reference) copy."