Fixes

plugs/collab/collab.ts

@@ -172,6 +172,7 @@ const clientId = store.get("collabClientId").then(async (clientId) => {
   return clientId;
 });
 
+let lastCollabPage: string | undefined;
 let currentCollabId: string | undefined;
 
 const localCollabServer = location.protocol === "http:"
@@ -189,16 +190,18 @@ async function ping() {
     if (!collabId && currentCollabId) {
       // Stop collab
       console.log("Stopping collab");
+      if (lastCollabPage === currentPage) {
         editor.flashNotification(
           "Other users have left this page, switched back to single-user mode.",
         );
+      }
       currentCollabId = undefined;
       await collab.stop();
     } else if (collabId && collabId !== currentCollabId) {
       // Start collab
       console.log("Starting collab");
       editor.flashNotification(
-        "Another device has joined this page, switched to multi-user mode.",
+        "Opening page in multi-user mode.",
       );
       currentCollabId = collabId;
       await collab.start(
@@ -207,6 +210,9 @@ async function ping() {
         "you",
       );
     }
+    if (currentCollabId) {
+      lastCollabPage = currentPage;
+    }
   } catch (e: any) {
     // console.error("Ping error", e);
     if (e.message.includes("Failed to fetch") && currentCollabId) {

server/collab.ts

@@ -111,7 +111,20 @@ export class CollabServer {
       quiet: true,
       onLoadDocument: async (doc) => {
         console.log("[Hocuspocus]", "Requesting doc load", doc.documentName);
-        const pageName = doc.documentName.split("/").slice(1).join("/");
+        const [collabId, ...pageNamePieces] = doc.documentName.split("/");
+        const pageName = pageNamePieces.join("/");
+        const collabPage = this.pages.get(pageName);
+        if (!collabPage || collabPage.collabId !== collabId) {
+          // This can happen after a server restart, where old clients are still trying to continue on an old session
+          // This will self-correct when the client discovers that the collabId has changed
+          // Until then: HARD PASS (meaning: don't send a document)
+          console.warn(
+            "[Hocuspocus]",
+            "Client tried to connect to old session",
+            doc.documentName,
+          );
+          return;
+        }
         try {
           const yText = doc.document.getText("codemirror");
           const { data } = await this.spacePrimitives.readFile(