diff --git a/frontend/src/chat.js b/frontend/src/chat.js
new file mode 100644
index 0000000..9912d88
--- /dev/null
+++ b/frontend/src/chat.js
@@ -0,0 +1,410 @@
+import { ref, computed } from 'vue';
+
+import * as backend from './backend';
+import * as runs from './runs';
+import * as ui from './ui';
+
+// === Thread Helpers === //
+
+const THREAD_STALE_MS = 10 * 60 * 1000;
+
+function messageTime (message) {
+  // Accept the common backend timestamp field names and formats
+  const t = message.timestamp ?? message.time ?? message.createdAt;
+  if (t == null) return null;
+  const ms = typeof t == 'number' ? (t < 1e12 ? t * 1000 : t) : Date.parse(t);
+  return isNaN(ms) ? null : ms;
+}
+
+function isMessageStale (message) {
+  const time = messageTime(message);
+  // No timestamp available -> treat as stale; a new thread is the safer default
+  return time == null || (Date.now() - time) > THREAD_STALE_MS;
+}
+
+
+// === Chat Session === //
+
+// State and logic of one open chat, decoupled from the document.
+// The view creates a session, hooks onRescroll() to its message container,
+// and drives it with load()/unload(). Shared state is exposed as refs.
+export class ChatSession {
+  constructor () {
+    // Chat state
+    this.chat = ref({});
+    this.messages = ref([]);
+    this.unsentMessages = ref([]);
+    this.currentThreadId = ref(null);
+    this.isNewThread = ref(true); // "New Thread" UI state
+    this.messageRunMap = ref({}); // messageId -> runId of the run it started
+
+    // Editing state
+    this.editingMessageId = ref(null);
+    this.noteMode = ref(false);
+
+    this.chatEntries = computed(() => {
+      return this.computeChatEntries(
+        this.messages.value.concat(this.unsentMessages.value)
+      );
+    });
+
+    this.editInfo = computed(() => {
+      const parts = [this.isNewThread.value ? 'New Thread' : `Thread ${this.currentThreadId.value}`];
+      if (this.editingMessageId.value != null) {
+        if (this.noteMode.value) {
+          parts.push(`Editing Note ${this.editingMessageId.value}`);
+        } else {
+          parts.push(`Editing ${this.editingMessageId.value}`);
+        }
+      } else if (this.noteMode.value) {
+        parts.push('Editing Note');
+      }
+      return parts.join(' - ');
+    });
+
+    // Internals
+    this.chatId = null;
+    this.agentNames = {};
+    // TODO: user sent messages are added without an id; send-chat-message
+    // should return the message id instead of matching by content
+    this._messageNonce = 1;
+    this._unsubscribeChat = null;
+    this._unsubscribeRuns = null;
+    this._runListener = null;
+    this._rescroll = null;
+  }
+
+  // The view injects a hook that re-scrolls its message container
+  onRescroll (callback) {
+    this._rescroll = callback;
+  }
+
+  rescroll (options) {
+    if (this._rescroll) this._rescroll(options);
+  }
+
+
+  // === Loading === //
+
+  async load (chatId) {
+    this.unload();
+    this.chatId = chatId;
+
+    // Reset state
+    this.chat.value = {};
+    this.messages.value = [];
+    this.unsentMessages.value = [];
+    this.messageRunMap.value = {};
+    this.currentThreadId.value = null;
+    this.isNewThread.value = true;
+    this.editingMessageId.value = null;
+    this.noteMode.value = false;
+
+    // Create an agent name dictionary
+    const agents = await backend.getAgents();
+    if (this.chatId != chatId) return; // A newer load or unload has won
+    this.agentNames = {};
+    for (let agent of agents) {
+      this.agentNames[agent.id] = agent.name;
+    }
+
+    backend.getChat(chatId).then(info => {
+      if (this.chatId == chatId) {
+        this.chat.value = Object.assign({}, info);
+      }
+    });
+
+    this._unsubscribeChat = backend.onChatMessages(chatId, it => this.receiveMessage(it));
+    this._unsubscribeRuns = runs.onChatMessage(chatId, event => this.trackRun(event));
+
+    const response = await backend.sendAction("get-chat-messages", {chatId});
+    if (this.chatId != chatId) return;
+
+    // Always good to duplicate when assigning to a ref
+    this.messages.value = response.messages.map(it => ({
+      id: this._messageNonce++,
+      type: it.kind,
+      subkind: it.subkind,
+      sender: it.sender,
+      content: it.content,
+      threadId: it.threadId,
+    }));
+
+    // Continue the last thread only if it is recent (under 10 minutes old);
+    // otherwise start in "New Thread" state
+    const lastMessage = response.messages[response.messages.length - 1];
+    if (lastMessage && lastMessage.threadId != null && !isMessageStale(lastMessage)) {
+      this.currentThreadId.value = lastMessage.threadId;
+      this.isNewThread.value = false;
+    }
+
+    // Must happen on the same async-thread that sets `messages`
+    this.rescroll({forceBottom: true});
+  }
+
+  unload () {
+    this.chatId = null;
+    if (this._unsubscribeChat) this._unsubscribeChat();
+    this._unsubscribeChat = null;
+    if (this._unsubscribeRuns) this._unsubscribeRuns();
+    this._unsubscribeRuns = null;
+    if (this._runListener) this._runListener.cancel();
+    this._runListener = null;
+  }
+
+
+  // === Incoming Messages === //
+
+  // Handles a chat message broadcast from the backend
+  receiveMessage (it) {
+    if (it.update) {
+      // Find message in list. If not found, add it
+      for (let entry of this.messages.value) {
+        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;
+          return;
+        }
+      }
+    }
+
+    if (it.sender == 'user') {
+      let unsent = this.unsentMessages.value.shift();
+      if (unsent) {
+        if (unsent.content == it.content) {
+          unsent.id = it.id;
+          unsent.threadId = it.threadId;
+          this.addMessage(unsent);
+          return;
+        } else {
+          // Remove from unsent list and add message as received
+          ui.alert("TODO: update unsent message");
+        }
+      }
+    }
+
+    this.addMessage({
+      id: it.id,
+      type: it.kind,
+      subkind: it.subkind,
+      format: it.format,
+      sender: it.sender,
+      content: it.content,
+      threadId: it.threadId,
+    });
+  }
+
+
+  // === Run Tracking === //
+
+  // Tracks the run started by a message, so the view can offer cancellation
+  trackRun (event) {
+    if (!this._runListener) {
+      this._runListener = runs.addRunListener(run => this.onRunUpdate(run));
+    }
+    this._runListener.addRunId(event.runId);
+    this.messageRunMap.value[event.messageId] = event.runId;
+  }
+
+  onRunUpdate (run) {
+    if (!run.done) return;
+    // TODO: RunListener should expose a removeRunId() method
+    this._runListener.runIds.delete(run.id);
+    const map = this.messageRunMap.value;
+    for (let messageId in map) {
+      if (map[messageId] == run.id) {
+        delete map[messageId];
+      }
+    }
+  }
+
+  cancelMessageRun (messageId) {
+    const runId = this.messageRunMap.value[messageId];
+    if (runId != null) runs.cancelRun(runId);
+  }
+
+
+  // === Sending === //
+
+  addMessage (message, options={}) {
+    this.rescroll();
+    if (options.unsent) {
+      message.id = this._messageNonce++;
+      this.unsentMessages.value.push(message);
+    } else {
+      this.messages.value.push(message);
+    }
+  }
+
+  // Sends a new user message, or updates the one being edited.
+  // `kind`/`subkind` produce special messages (notes, resources, ...).
+  // Returns false when nothing was sent, so the view can restore its input.
+  async sendMessage (content, { kind=null, subkind=null } = {}) {
+    if (!content || !content.trim()) return false;
+    if (kind == null && this.noteMode.value) kind = 'note';
+
+    const messageId = this.editingMessageId.value;
+
+    if (messageId == null) {
+      // "New Thread" is a UI state: the thread is only created upstream
+      // here, once there is a message to put into it
+      const threadId = await this.resolveSendThread();
+      if (threadId == null) return false;
+
+      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);
+        }
+      });
+
+      this.addMessage({
+        type: kind || 'message',
+        subkind,
+        sender: 'user',
+        content,
+        threadId,
+      }, {unsent: true});
+    } else {
+      const messageRef = this.messages.value.find(it => it.id == messageId);
+
+      backend.sendAction("update-chat-message", {
+        messageId, content, kind,
+      }).then(response => {
+        if (response && response.error) {
+          ui.alert("Error updating message: " + response.error);
+        }
+      });
+
+      messageRef.type = kind || 'message';
+      messageRef.content = content;
+      this.editingMessageId.value = null;
+    }
+
+    if (kind == 'note') this.noteMode.value = false;
+    return true;
+  }
+
+  // Returns the threadId to send into, creating the thread upstream
+  // if we're in "New Thread" state
+  async resolveSendThread () {
+    if (!this.isNewThread.value) return this.currentThreadId.value;
+
+    const res = await backend.sendAction("create-chat-thread", {chatId: this.chatId});
+    if (res.threadId == null) {
+      ui.alert("Error creating thread" + (res.error ? `: ${res.error}` : ""));
+      return null;
+    }
+    this.currentThreadId.value = res.threadId;
+    this.isNewThread.value = false;
+    return res.threadId;
+  }
+
+  // Begins or ends message editing; the view keeps its input field in sync
+  setEditing (messageId) {
+    this.editingMessageId.value = messageId ?? null;
+  }
+
+
+  // === Threads === //
+
+  activateThread (threadId) {
+    if (threadId == null) return; // "New Thread" placeholder isn't clickable
+    // Continuing a thread: it becomes the one open thread
+    this.currentThreadId.value = threadId;
+    this.isNewThread.value = false;
+    this.rescroll();
+  }
+
+  startNewThread () {
+    // Pure UI state — nothing is created upstream until a message is sent
+    this.isNewThread.value = true;
+    this.currentThreadId.value = null;
+    this.rescroll();
+  }
+
+
+  // === Entry Computation === //
+
+  // Builds the display list: the active thread's messages in order, every
+  // other thread collapsed into a single preview header
+  computeChatEntries (messages) {
+    let entries = [];
+    let threadGroups = {}; // Map<int, message[]>
+
+    const senderName = (sender) => {
+      let isInt = !isNaN(parseInt(sender));
+      if (isInt) {
+        return this.agentNames[sender] || `<agent-${sender}>`;
+      } else {
+        return sender;
+      }
+    };
+
+    const addThreadHeader = (threadId, group, options={}) => {
+      let preview = null;
+      const last = group[group.length - 1];
+      if (last && !options.active) {
+        let content = String(last.content || '').split('\n')[0].trim();
+        if (content.length > 100) content = content.slice(0, 100) + '…';
+        preview = {sender: senderName(last.sender), content};
+      }
+      entries.push({
+        type: 'thread-header',
+        threadId,
+        active: !!options.active,
+        messageCount: group.length,
+        preview,
+      });
+    };
+
+    // First pass: Group messages by thread
+    for (let message of messages) {
+      if (message.threadId != null) {
+        let group = threadGroups[message.threadId] ||
+          (threadGroups[message.threadId] = []);
+        group.push(message);
+      }
+    }
+
+    // Only the active thread is ever open; every other thread collapses
+    // into a single preview header
+    const activeThreadId = this.isNewThread.value ? null : this.currentThreadId.value;
+    let activeHeaderAdded = false;
+
+    // Second pass: Build the display list with correct ordering
+    for (let _msg of messages) {
+      const message = Object.assign({}, _msg, {sender: senderName(_msg.sender)});
+
+      if (message.threadId == null) {
+        entries.push(message);
+        continue;
+      }
+
+      let threadId = message.threadId;
+      let group = threadGroups[threadId];
+
+      if (threadId === activeThreadId) {
+        if (!activeHeaderAdded) {
+          addThreadHeader(threadId, group, {active: true});
+          activeHeaderAdded = true;
+        }
+        entries.push(message);
+      } else if (message.id == group[group.length - 1].id) {
+        // Collapsed: one preview card in place of the thread's last message
+        addThreadHeader(threadId, group);
+      }
+    }
+
+    // "New Thread" UI state: placeholder where the new thread will start
+    if (this.isNewThread.value) {
+      addThreadHeader(null, []);
+    }
+
+    return entries;
+  }
+}
\ No newline at end of file
diff --git a/frontend/src/views/Chat.vue b/frontend/src/views/Chat.vue
index ee35898..17421b5 100644
--- a/frontend/src/views/Chat.vue
+++ b/frontend/src/views/Chat.vue
@@ -1,6 +1,6 @@
 <script setup>
   import {
-    ref, watch, computed,
+    ref, watch,
     onMounted, onUnmounted,
   } from "vue";
 
@@ -9,7 +9,7 @@
 
   import * as backend from '../backend';
   import * as ui from '../ui';
-  import * as runs from '../runs';
+  import { ChatSession } from '../chat';
 
   const props = defineProps({
     id: {
@@ -18,224 +18,36 @@
     },
   });
 
-  let chatId = null;
-  let agentNames = {};
+  // Chat state and logic live in the session; the view binds to its refs
+  const session = new ChatSession();
+  const {
+    chat, chatEntries, editInfo,
+    noteMode, editingMessageId, messageRunMap,
+  } = session;
 
-  // Chat State
-  const chat = ref({});
-  const messages = ref([]);
-  const unsentMessages = ref([]);
-  const currentThreadId = ref(null);
-  const chatEntries = computed(() => {
-    return computeChatEntries(messages.value.concat(unsentMessages.value));
-  });
-
-  // UI State
-  const isNewThread = ref(true); // "New Thread" UI state
-  const editingMessageId = ref(null);
-  const noteMode = ref(false);
-  const messageRunMap = ref({});
+  // UI state coupled to the document itself
   const expandedLogs = ref({}); // Message ids of logs currently expanded
-
-  const editInfo = computed(() => {
-    const parts = [isNewThread.value ? 'New Thread' : `Thread ${currentThreadId.value}`]
-    if (editingMessageId.value != null) {
-      if (noteMode.value) {
-        parts.push(`Editing Note ${editingMessageId.value}`);
-      } else {
-        parts.push(`Editing ${editingMessageId.value}`);
-      }
-    } else if (noteMode.value) {
-      parts.push('Editing Note');
-    }
-
-    return parts.join(' - ');
-  });
-
-  let _isMounted = false;
-  let unsubscribeChat = null;
-  let unsubscribeRuns = null;
-  let runListener = null;
-
-  // TODO: user sent message is added without id.
-  // User should receive his own message notification, and find its message to assign it an id.
-  // Alternatively, return the message id in send-chat-message action. Think thats better.
-  let _messageNonce = 1;
-
-
-  // === Thread Helpers === //
-
-  const THREAD_STALE_MS = 10 * 60 * 1000;
-
-  function messageTime (message) {
-    // Accept the common backend timestamp field names and formats
-    const t = message.timestamp ?? message.time ?? message.createdAt;
-    if (t == null) return null;
-    const ms = typeof t == 'number' ? (t < 1e12 ? t * 1000 : t) : Date.parse(t);
-    return isNaN(ms) ? null : ms;
-  }
-
-  function isMessageStale (message) {
-    const time = messageTime(message);
-    // No timestamp available -> treat as stale; a new thread is the safer default
-    return time == null || (Date.now() - time) > THREAD_STALE_MS;
-  }
-
-
-  // === State Management === //
-
-  async function loadChatState (newId) {
-    // This line was converting newId into an integer.
-    // Some parts of the program may still rely on it.
-    chatId = newId;
-
-    // Create an agent name dictionary
-    const _agents = await backend.getAgents();
-    for (let agent of _agents) {
-      agentNames[agent.id] = agent.name;
-    }
-
-    backend.getChat(chatId).then(info => {
-      chat.value = Object.assign({}, info);
-    });
-
-    unsubscribeChat = backend.onChatMessages(chatId, it => {
-      if (it.update) {
-        // Find message in list. If not found, add it
-        for (let entry of messages.value) {
-          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;
-            return;
-          }
-        }
-      }
-
-      if (it.sender == 'user') {
-        let unsent = unsentMessages.value.shift();
-        if (unsent) {
-          if (unsent.content == it.content) {
-            unsent.id = it.id;
-            unsent.threadId = it.threadId;
-            addMessage(unsent);
-            return;
-          } else {
-            // Remove from unsent list and add message as received
-            ui.alert("TODO: update unsent message");
-          }
-        }
-      }
-
-      addMessage({
-        id: it.id,
-        type: it.kind,
-        subkind: it.subkind,
-        format: it.format,
-        sender: it.sender,
-        content: it.content,
-        threadId: it.threadId,
-      });
-    });
-
-    unsubscribeRuns = runs.onChatMessage(chatId, onRunMessage);
-
-    let response = await backend.sendAction("get-chat-messages", {chatId});
-    // Always good to duplicate when assigning to a ref
-    messages.value = response.messages.map(it => ({
-      //id: it.id,
-      id: _messageNonce++,
-      type: it.kind,
-      subkind: it.subkind,
-      sender: it.sender,
-      content: it.content,
-      threadId: it.threadId,
-    }));
-
-    // Continue the last thread only if it is recent (under 10 minutes old);
-    // otherwise start in "New Thread" state
-    if (response.messages.length > 0) {
-      const lastMessage = response.messages[response.messages.length - 1];
-      if (lastMessage.threadId != null && !isMessageStale(lastMessage)) {
-        activateThread(lastMessage.threadId);
-      } else {
-        startNewThread();
-      }
-    } else {
-      startNewThread();
-    }
-
-    // This must happen on the same async-thread that sets `messages`
-    requestRescroll({forceBottom: true});
-
-    // Reset UI State
-    editingMessageId.value = null;
-    noteMode.value = false;
-    // thread state was set above; no need to reset
-  }
-
-  async function unloadChatState () {
-    if (unsubscribeChat) unsubscribeChat();
-    unsubscribeChat = null;
-    if (unsubscribeRuns) unsubscribeRuns();
-    unsubscribeRuns = null;
-  }
-
-  function onRunMessage (event) {
-    if (!runListener) {
-      runListener = runs.addRunListener(onRunUpdate);
-    }
-    runListener.addRunId(event.runId);
-    messageRunMap.value[event.messageId] = event.runId;
-  }
-  
-  function onRunUpdate (newRun) {
-    if (newRun.done) {
-      runListener.runIds.delete(newRun.id);
-      let map = messageRunMap.value;
-      for (let messageId in map) {
-        if (map[messageId] == newRun.id) {
-          delete map[messageId];
-        }
-      }
-    }
-  }
-
-  // This won't fire when called, the mounted callback will take care
-  watch(() => props.id, newId => {
-    if (_isMounted) {
-      unloadChatState();
-      loadChatState(newId);
-    }
-  })
-
-  onMounted(async () => {
-    _isMounted = true;
-    loadChatState(props.id);
-  });
-
-  onUnmounted(async () => {
-    _isMounted = false;
-    unloadChatState();
-  });
-
-
-  // === Chat Functionality === //
-
   const inputFieldElem = ref(null);
   const chatContainerElem = ref(null);
 
-  function addMessage (message, options={}) {
-    requestRescroll();
-    if (options.unsent) {
-      message.id = _messageNonce++;
-      unsentMessages.value.push(message);
-    } else {
-      messages.value.push(message);
-    }
-  }
+  let _isMounted = false;
+
+  watch(() => props.id, newId => {
+    if (_isMounted) session.load(newId);
+  });
+
+  onMounted(() => {
+    _isMounted = true;
+    session.onRescroll(requestRescroll); // function declarations are hoisted
+    session.load(props.id);
+  });
+
+  onUnmounted(() => {
+    _isMounted = false;
+    session.unload();
+  });
+
+  // === Chat Functionality === //
 
   async function sendMessage () {
     let elem = inputFieldElem.value;
@@ -243,159 +55,9 @@
     let content = elem.innerText;
     elem.innerText = "";
 
-    if (!content.trim()) return; // Don't send empty messages
-
-    let messageId = editingMessageId.value;
-    let isNote = noteMode.value;
-
-    if (messageId == null) {
-      // "New Thread" is a UI state: the thread is only created upstream
-      // here, once there is a message to put into it
-      let threadId = await resolveSendThread();
-      if (threadId == null) {
-        elem.innerText = content; // let the user retry
-        return;
-      }
-
-      backend.sendAction("send-chat-message", {
-        chatId, content, threadId,
-        kind: isNote ? 'note' : null,
-      }).then((response) => {
-        if (response['error']) {
-          ui.alert("Error sending chat message: " + response['error']);
-        }
-      });
-
-      const newMessage = {
-        type: isNote ? 'note' : 'message',
-        sender: 'user',
-        content,
-        threadId,
-      };
-      addMessage(newMessage, {unsent: true});
-    } else {
-      const messageRef = messages.value.find((it) => it.id == messageId);
-
-      backend.sendAction("update-chat-message", {
-        messageId, content,
-        'kind': isNote ? 'note' : null,
-      }).then((response) => {
-        if (response['error']) {
-          ui.alert("Error updating message: " + response['error']);
-        }
-      });
-
-      messageRef.type = isNote ? 'note' : 'message';
-      messageRef.content = content;
-    }
-
-    if (isNote) noteMode.value = false;
-  }
-
-  async function resolveSendThread () {
-    // Returns the threadId to send into, creating the thread upstream
-    // if we're in "New Thread" state
-    if (!isNewThread.value) return currentThreadId.value;
-
-    const res = await backend.sendAction("create-chat-thread", {chatId});
-    if (res.threadId == null) {
-      ui.alert("Error creating thread" + (res.error ? `: ${res.error}` : ""));
-      return null;
-    }
-    currentThreadId.value = res.threadId;
-    isNewThread.value = false;
-    return res.threadId;
-  }
-
-  function computeChatEntries (messages) {
-    let entries = [];
-    let threadGroups = {}; // Map<int, message[]>
-
-    function senderName (sender) {
-      let isInt = !isNaN(parseInt(sender));
-      if (isInt) {
-        return agentNames[sender] || `<agent-${sender}>`;
-      } else {
-        return sender;
-      }
-    }
-
-    function addThreadHeader (threadId, group, options={}) {
-      let preview = null;
-      const last = group[group.length - 1];
-      if (last && !options.active) {
-        let content = String(last.content || '').split('\n')[0].trim();
-        if (content.length > 100) content = content.slice(0, 100) + '…';
-        preview = {sender: senderName(last.sender), content};
-      }
-      entries.push({
-        type: 'thread-header',
-        threadId,
-        active: !!options.active,
-        messageCount: group.length,
-        preview,
-      });
-    }
-
-    // First pass: Group messages by thread
-    for (let message of messages) {
-      if (message.threadId != null) {
-        let group = threadGroups[message.threadId] ||
-          (threadGroups[message.threadId] = []);
-        group.push(message);
-      }
-    }
-
-    // Only the active thread is ever open; every other thread collapses
-    // into a single preview header
-    const activeThreadId = isNewThread.value ? null : currentThreadId.value;
-    let activeHeaderAdded = false;
-
-    // Second pass: Build the display list with correct ordering
-    for (let _msg of messages) {
-      const message = Object.assign({}, _msg, {sender: senderName(_msg.sender)});
-
-      if (message.threadId == null) {
-        entries.push(message);
-        continue;
-      }
-
-      let threadId = message.threadId;
-      let group = threadGroups[threadId];
-
-      if (threadId === activeThreadId) {
-        if (!activeHeaderAdded) {
-          addThreadHeader(threadId, group, {active: true});
-          activeHeaderAdded = true;
-        }
-        entries.push(message);
-      } else if (message.id == group[group.length - 1].id) {
-        // Collapsed: one preview card in place of the thread's last message
-        addThreadHeader(threadId, group);
-      }
-    }
-
-    // "New Thread" UI state: placeholder where the new thread will start
-    if (isNewThread.value) {
-      addThreadHeader(null, []);
-    }
-
-    return entries;
-  }
-
-  function activateThread (threadId) {
-    if (threadId == null) return; // "New Thread" placeholder isn't clickable
-    // Continuing a thread: it becomes the one open thread
-    currentThreadId.value = threadId;
-    isNewThread.value = false;
-    requestRescroll();
-  }
-
-  function startNewThread () {
-    // Pure UI state — nothing is created upstream until a message is sent
-    isNewThread.value = true;
-    currentThreadId.value = null;
-    requestRescroll();
+    // False when nothing was sent (empty input or thread creation failed)
+    const ok = await session.sendMessage(content);
+    if (!ok) elem.innerText = content; // let the user retry
   }
 
   async function addRemoteResource () {
@@ -412,36 +74,14 @@
     })));
     if (!selected) return;
 
-    const threadId = await resolveSendThread();
-    if (threadId == null) return;
-    backend.sendAction("send-chat-message", {
-      chatId, content: selected, threadId,
-      kind: 'resource', subkind: 'remote',
-    }).then((response) => {
-      if (response['error']) {
-        ui.alert("Error adding remote: " + response['error']);
-      }
-    });
-
-    // Optimistic entry, matched against the server broadcast by content
-    addMessage({
-      type: 'resource',
-      subkind: 'remote',
-      sender: 'user',
-      content: selected,
-      threadId,
-    }, {unsent: true});
+    // Sends a 'resource' message into the current (or a new) thread
+    await session.sendMessage(selected, {kind: 'resource', subkind: 'remote'});
   }
 
   function editMessage (message) {
     let elem = inputFieldElem.value;
-    if (message) {
-      editingMessageId.value = message.id;
-      elem.innerText = message.content;
-    } else {
-      editingMessageId.value = null;
-      elem.innerText = "";
-    }
+    elem.innerText = message ? message.content : "";
+    session.setEditing(message ? message.id : null);
   }
 
   async function deleteChat (chat) {
@@ -520,14 +160,14 @@
     const elem = chatContainerElem.value;
 
     const scroll = elem.scrollTop;
-    const max = elem.scrollTopMax;
+    const max = elem.scrollHeight - elem.clientHeight;
 
     // Rescroll in 2 frames
     window.requestAnimationFrame(() => {
       window.requestAnimationFrame(() => {
         // Chat was fully scrolled down
         if (forceBottom || scroll == max) {
-          elem.scrollTop = elem.scrollTopMax;
+          elem.scrollTop = max;
         } else if (bottomRelative) {
           // TODO: Keep scroll at the same distance from the bottom.
           // This will be used when the user scrolls to the top and previous messages are loaded
@@ -563,13 +203,13 @@
         :key="msg.id ?? ('thread-' + msg.threadId)" 
         :message="msg" 
         @open-menu="chatEntryContextMenu"
-        @open-thread="activateThread"
+        @open-thread="session.activateThread"
 
         :log-expanded="expandedLogs[msg.id]"
         @toggle-log="toggleLogExpand(msg)"
 
         :cancellable="messageRunMap[msg.id]"
-        @cancel="runs.cancelRun(messageRunMap[msg.id])"
+        @cancel="session.cancelMessageRun(msg.id)"
       />
     </div>
 
@@ -581,7 +221,7 @@
       <div class="input-field" ref="inputFieldElem" @keydown="inputKeyDown($event)" contenteditable></div>
 
       <div class="input-row">
-        <button @click="startNewThread()">
+        <button @click="session.startNewThread()">
           New Thread
         </button>
         <button @click="addRemoteResource()">