diff --git a/backend/src/server/websocket.py b/backend/src/server/websocket.py
index 3df1a43..6ace764 100644
--- a/backend/src/server/websocket.py
+++ b/backend/src/server/websocket.py
@@ -285,7 +285,7 @@ def register(server, app, auth_manager):
                 elif action == "fork-chat-thread":
                     thread_id = await app.fork_chat_thread(
                         thread_id=body['threadId'],
-                        message_id=body['messageId'],
+                        message_id=body.get('messageId'),
                     )
                     await send({'message': "chat thread created", 'threadId': thread_id, 'nonce': nonce})
 
diff --git a/frontend/src/chat.js b/frontend/src/chat.js
index bc199af..02e1558 100644
--- a/frontend/src/chat.js
+++ b/frontend/src/chat.js
@@ -251,21 +251,36 @@ export class ChatSession {
   // Handles a chat message broadcast from the backend
   receiveMessage (it) {
     if (it.update) {
-      // Find message in list. If not found, add it
-      for (let thread of this.threads) {
-        for (let entry of thread.messages) {
-          if (entry.id == it.id) {
-            entry.type = it.kind;
-            entry.subkind = it.subkind;
-            entry.format = it.format;
-            entry.content = it.content;
-            entry.threadId = it.threadId;
+      // TODO: if threadId changed, the old message has to be searched
 
-            this.computeChatEntries();
-            return;
-          }
+      let thread = this.getThread(it.threadId);
+
+      for (let entry of thread.messages) {
+        if (entry.id == it.id) {
+          entry.type = it.kind;
+          entry.subkind = it.subkind;
+          entry.format = it.format;
+          entry.content = it.content;
+
+          // If this changes, message has to get moved
+          entry.threadId = it.threadId;
+
+          this.computeChatEntries();
+          return;
         }
       }
+
+      // Message not found in target thread
+      // Find the old message
+      ui.alert("TODO: find updated messages in different threads");
+      //let stack = Array.from(this.threads);
+      let oldMessage = null;
+
+      // if we didn't find it, add it like a new one
+      if (oldMessage) {
+        ui.alert("TODO: move a message with updated thread");
+        return;
+      }
     }
 
     if (it.sender == 'user') {
@@ -351,16 +366,34 @@ export class ChatSession {
     if (kind == null && this.noteMode.value) kind = 'note';
 
     const messageId = this.editingMessageId.value;
-    const threadId = await this.resolveTargetThread();
 
-    if (messageId == null || this.creatingThread.value) {
-      // New message in target thread (maybe fork)
+    if (messageId == null) {
+      let threadId = this.currentThreadId.value;
+
+      // New message creating threads fork the current thread
+      if (this.creatingThread.value) {
+        let res;
+        if (threadId == null) {
+          res = await backend.sendAction("create-chat-thread", {
+            chatId: this.chatId,
+          });
+        } else {
+          res = await backend.sendAction("fork-chat-thread", {
+            chatId: this.chatId,
+            threadId: threadId,
+          });
+        }
+
+        threadId = res.threadId;
+      }
 
       backend.sendAction("send-chat-message", {
         chatId: this.chatId, content, threadId, kind, subkind,
-      }).then(response => {
-        if (response && response.error) {
-          ui.alert("Error sending chat message: " + response.error);
+      }).then(res => {
+        if (res.error) {
+          ui.alert("Error sending chat message: " + res.error);
+        } else {
+          this.activateThread(threadId);
         }
       });
 
@@ -373,24 +406,90 @@ export class ChatSession {
       }, {unsent: true});
 
     } else {
-      // Editing existing message
+      // Editing or forking a message
 
-      backend.sendAction("update-chat-message", {
-        messageId, content, kind,
-      }).then(response => {
-        if (response && response.error) {
-          ui.alert("Error updating message: " + response.error);
+      // Find the threads of the message and it's predecessor
+      let messageThreadId;
+      let previousThreadId;
+
+      let thread = this.getThread(this.currentThreadId.value);
+      while (thread) {
+        let index = thread.messages.findIndex(it => it.id == messageId);
+        if (index >= 0) {
+          messageThreadId = thread.id;
+          if (index == 0) {
+            previousThreadId = thread.parentId;
+          } else {
+            previousThreadId = thread.id;
+          }
+          break;
+        } else if (thread.parentId) {
+          thread = this.getThread(thread.parentId);
+        } else {
+          ui.alert("Target message not found in active threads: " + messageId);
+          return;
         }
-      });
+      }
+
+      if (this.creatingThread.value) {
+
+        // Send the target message to a fork
+        let res = await backend.sendAction("fork-chat-thread", {
+          chatId: this.chatId,
+          threadId: previousThreadId,
+          messageId,
+        });
+
+        // Then create a new fork again for the new message
+        res = await backend.sendAction("fork-chat-thread", {
+          chatId: this.chatId,
+          threadId: previousThreadId,
+        });
+
+        let newThreadId = res.threadId;
+        this.getThread(newThreadId).update({parentId: previousThreadId});
+
+        // Send in new thread
+        backend.sendAction("send-chat-message", {
+          chatId: this.chatId,
+          threadId: newThreadId,
+          content, kind, subkind,
+        }).then(res => {
+          if (res.error) {
+            ui.alert("Error sending chat message: " + res.error);
+          } else {
+            this.activateThread(newThreadId);
+          }
+        });
+
+        this.addMessage({
+          type: kind || 'message',
+          subkind,
+          sender: 'user',
+          content,
+          threadId: newThreadId,
+        }, {unsent: true});
 
-      // No update event received, local manual update
-      let thread = await this.getThread(threadId);
-      let existing = thread.messages.find(msg => msg.id == messageId);
-      if (existing) {
-        existing.content = content;
-        existing.type = kind || 'message';
       } else {
-        console.error("Can't edit locally?", {messageId, threadId, t_m: thread.messages});
+
+        // Editing existing message
+        backend.sendAction("update-chat-message", {
+          messageId, content, kind,
+        }).then(response => {
+          if (response && response.error) {
+            ui.alert("Error updating message: " + response.error);
+          }
+        });
+
+        // No update event received, local manual update
+        let thread = await this.getThread(messageThreadId);
+        let existing = thread.messages.find(msg => msg.id == messageId);
+        if (existing) {
+          existing.content = content;
+          existing.type = kind || 'message';
+        } else {
+          console.error("Can't edit locally?", {messageId, thread});
+        }
       }
 
       this.editingMessageId.value = null;
@@ -419,8 +518,9 @@ export class ChatSession {
   }
 
   // Begins or ends message editing; the view keeps its input field in sync
-  setEditing (messageId) {
+  setEditing (messageId, fork) {
     this.editingMessageId.value = messageId ?? null;
+    this.creatingThread.value = Boolean(fork);
   }
 
   // Adds a bulk of messages to the message list, in their correct