src/components/DeadlineTimer.ts

@@ -1,5 +1,6 @@
 import * as Y from "yjs";
 import { getDeadline } from "../state";
+import { enforceAppendOnly } from "../yDocUtil";
 
 const DEADLINE_DURATION_MS = 2 * 60 * 1000; // 2 minutes
 
@@ -79,7 +80,7 @@ export function DeadlineTimer(
     onClearDeadline();
   });
 
-  deadlineMap.observe(() => render());
+  deadlineMap.observe(enforceAppendOnly(deadlineMap,render));
   render();
 
   return wrapper;

src/components/PollList.ts

@@ -1,6 +1,7 @@
 import * as Y from "yjs";
 import type { OptionRecord } from "../state";
 import { PollOption } from "./PollOption";
+import { enforceAppendOnly } from "../yDocUtil";
 
 export function PollList(
   yOptions: Y.Map<OptionRecord>,
@@ -119,8 +120,8 @@ export function PollList(
     });
   }
 
-  yOptions.observeDeep(() => render());
+  yOptions.observe(enforceAppendOnly(yOptions,render));
-  yVotes.observe(() => render());
+  yVotes.observe(enforceAppendOnly(yVotes,render));
   render();
 
   return wrapper;

src/yDocUtil.ts

@@ -0,0 +1,33 @@
+import * as Y from "yjs";
+
+/**
+ * Enforces append-only logic on a Y.Map.
+ * Reverts any 'update' or 'delete' actions detected in the observer.
+ */
+export function enforceAppendOnly(yMap: Y.Map<any>,render: () => void) {
+  return (event: Y.YMapEvent<any>, transaction: Y.Transaction) => {
+    // Avoid infinite loops: check if this change was 
+    // triggered by our own 'undo' logic.
+    if (transaction.origin === 'revert-logic') return;
+
+    event.keys.forEach((change, key) => {
+      const { action, oldValue } = change;
+
+      if (action === 'update' || action === 'delete') {
+        // Use the transaction to undo the illegal operation
+        yMap.doc?.transact(() => {
+          if (action === 'update' && oldValue !== undefined) {
+            // Revert to previous value
+            yMap.set(key, oldValue);
+          } else if (action === 'delete' && oldValue !== undefined) {
+            // Restore the deleted key
+            yMap.set(key, oldValue);
+          }
+          console.warn(`Illegal ${action} attempt on key: "${key}". Reverted.`);
+        }, 'revert-logic'); 
+      }
+    });
+
+    render();
+  };
+}