feat(ai-chat): queue messages typed while the agent is streaming

Previously a message composed while the AI agent was streaming a reply was
silently dropped (the composer early-returned on isStreaming). Now such
messages are queued FIFO and sent automatically once the current turn
finishes cleanly.

- chat-input: submit() enqueues while streaming (via new onQueue prop) and
  sends otherwise; during streaming show a queue Send button (when text is
  present) alongside the Stop button; the textarea stays usable.
- chat-thread: per-conversation queue in local state (mirrored in a ref);
  flush the next message in onFinish ONLY on a clean finish - ai@6 useChat
  fires onFinish from a finally on Stop/disconnect/error too, where the queue
  must be preserved. Pending messages render as removable chips above the
  composer. Queue is cleared on chat switch (parent remount) and survives
  in-place new-chat id adoption.
- queue-helpers: pure FIFO helpers (enqueue/dequeue/removeQueuedById) + tests.
- i18n: add en-US/ru-RU keys (Queue message, Remove queued message,
  Send when the agent finishes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/client/public/locales/en-US/translation.json

@@ -1150,6 +1150,9 @@
   "AI agent is typing…": "AI agent is typing…",
   "{{name}} is typing…": "{{name}} is typing…",
   "Send": "Send",
+  "Send when the agent finishes": "Send when the agent finishes",
+  "Queue message": "Queue message",
+  "Remove queued message": "Remove queued message",
   "Stop": "Stop",
   "Chat menu": "Chat menu",
   "No chats yet.": "No chats yet.",

apps/client/public/locales/ru-RU/translation.json

@@ -693,6 +693,9 @@
   "Minimize": "Свернуть",
   "No chats yet.": "Чатов пока нет.",
   "Send": "Отправить",
+  "Send when the agent finishes": "Отправить, когда агент закончит",
+  "Queue message": "Поставить в очередь",
+  "Remove queued message": "Убрать из очереди",
   "Something went wrong": "Что-то пошло не так",
   "Stop": "Стоп",
   "The AI agent could not respond. Please try again.": "AI-агент не смог ответить. Попробуйте ещё раз.",

apps/client/src/features/ai-chat/components/ai-chat.module.css

@@ -128,3 +128,29 @@
 .conversationItemActive {
     background: var(--mantine-color-gray-light);
 }
+
+/* Pending messages queued by the user while a turn is still streaming. They
+   are sent automatically, FIFO, once the current turn finishes. */
+.queuedList {
+    padding-bottom: var(--mantine-spacing-xs);
+}
+
+.queuedItem {
+    background: var(--mantine-color-gray-light);
+    border-radius: var(--mantine-radius-sm);
+    padding: 4px 8px;
+}
+
+.queuedIcon {
+    flex: none;
+    color: var(--mantine-color-dimmed);
+}
+
+.queuedText {
+    flex: 1;
+    min-width: 0;
+    color: var(--mantine-color-dimmed);
+    white-space: pre-wrap;
+    overflow-wrap: break-word;
+    word-break: break-word;
+}

apps/client/src/features/ai-chat/components/chat-input.tsx

@@ -9,18 +9,24 @@ import { MicButton } from "@/features/dictation/components/mic-button";
 
 interface ChatInputProps {
   onSend: (text: string) => void;
+  /** Called instead of `onSend` while a turn is streaming: the text is queued
+   *  and sent automatically once the current turn finishes. */
+  onQueue: (text: string) => void;
   onStop: () => void;
   isStreaming: boolean;
   disabled?: boolean;
 }
 
 /**
- * Message composer. Enter sends, Shift+Enter inserts a newline. While the agent
- * is streaming, the send button becomes a Stop button (calls `stop()`); the
- * textarea stays usable so the user can draft the next turn.
+ * Message composer. Enter submits, Shift+Enter inserts a newline. While the
+ * agent is streaming, submitting QUEUES the message (via `onQueue`) instead of
+ * dropping it — it is sent automatically once the current turn finishes; the
+ * Stop button (calls `stop()`) is also shown. The textarea stays usable so the
+ * user can draft / queue the next turn while the agent is busy.
  */
 export default function ChatInput({
   onSend,
+  onQueue,
   onStop,
   isStreaming,
   disabled,
@@ -30,17 +36,18 @@ export default function ChatInput({
   const workspace = useAtomValue(workspaceAtom);
   const isDictationEnabled = workspace?.settings?.ai?.dictation === true;
 
-  const send = (): void => {
+  const submit = (): void => {
     const text = value.trim();
-    if (!text || isStreaming || disabled) return;
-    onSend(text);
+    if (!text || disabled) return;
+    if (isStreaming) onQueue(text);
+    else onSend(text);
     setValue("");
   };
 
   const handleKeyDown = (e: KeyboardEvent<HTMLTextAreaElement>): void => {
     if (e.key === "Enter" && !e.shiftKey) {
       e.preventDefault();
-      send();
+      submit();
     }
   };
 
@@ -70,23 +77,37 @@ export default function ChatInput({
         />
       )}
       {isStreaming ? (
-        <Tooltip label={t("Stop")} withArrow>
-          <ActionIcon
-            size="lg"
-            color="red"
-            variant="light"
-            onClick={onStop}
-            aria-label={t("Stop")}
-          >
-            <IconPlayerStopFilled size={18} />
-          </ActionIcon>
-        </Tooltip>
+        <Group gap="xs" wrap="nowrap">
+          {value.trim().length > 0 && (
+            <Tooltip label={t("Send when the agent finishes")} withArrow>
+              <ActionIcon
+                size="lg"
+                variant="filled"
+                onClick={submit}
+                aria-label={t("Queue message")}
+              >
+                <IconSend size={18} />
+              </ActionIcon>
+            </Tooltip>
+          )}
+          <Tooltip label={t("Stop")} withArrow>
+            <ActionIcon
+              size="lg"
+              color="red"
+              variant="light"
+              onClick={onStop}
+              aria-label={t("Stop")}
+            >
+              <IconPlayerStopFilled size={18} />
+            </ActionIcon>
+          </Tooltip>
+        </Group>
       ) : (
         <Tooltip label={t("Send")} withArrow>
           <ActionIcon
             size="lg"
             variant="filled"
-            onClick={send}
+            onClick={submit}
             disabled={disabled || value.trim().length === 0}
             aria-label={t("Send")}
           >

apps/client/src/features/ai-chat/components/chat-thread.tsx

@@ -1,7 +1,7 @@
-import { useMemo, useRef } from "react";
+import { useCallback, useMemo, useRef, useState } from "react";
 import { generateId } from "ai";
-import { Alert, Box, Stack } from "@mantine/core";
-import { IconAlertTriangle } from "@tabler/icons-react";
+import { ActionIcon, Alert, Box, Group, Stack, Text } from "@mantine/core";
+import { IconAlertTriangle, IconClockHour4, IconX } from "@tabler/icons-react";
 import { useTranslation } from "react-i18next";
 import { useChat, type UIMessage } from "@ai-sdk/react";
 import { DefaultChatTransport } from "ai";
@@ -13,6 +13,12 @@ import {
   IAiRole,
 } from "@/features/ai-chat/types/ai-chat.types.ts";
 import { describeChatError } from "@/features/ai-chat/utils/error-message.ts";
+import {
+  dequeue,
+  enqueueMessage,
+  removeQueuedById,
+  type QueuedMessage,
+} from "@/features/ai-chat/utils/queue-helpers.ts";
 import classes from "@/features/ai-chat/components/ai-chat.module.css";
 
 /** The page the user is currently viewing, sent as chat context. */
@@ -137,6 +143,48 @@ export default function ChatThread({
   // prepareSendMessagesRequest), so this purely-client store key can stay fixed.
   const chatStoreId = stableIdRef.current;
 
+  // Pending messages the user composed WHILE a turn was streaming. They are sent
+  // automatically, FIFO, on successful turn completion (`onFinish`). The queue is
+  // LOCAL state so it is scoped to this conversation: it is cleared when the user
+  // deliberately switches chat / starts a new chat (the parent remounts this via
+  // `key`), but it SURVIVES in-place new-chat id adoption (no remount), so a
+  // message queued during a brand-new chat's first turn is not lost. On Stop or
+  // error the queue is intentionally preserved (onFinish does not fire then) so
+  // the user decides what to do with the pending messages.
+  const [queued, setQueued] = useState<QueuedMessage[]>([]);
+  // Mirror the queue in a ref so the `onFinish` flush always reads the latest
+  // queue without a stale closure; `setQueue` updates BOTH the ref and the state.
+  const queuedRef = useRef<QueuedMessage[]>([]);
+  const setQueue = useCallback((next: QueuedMessage[]) => {
+    queuedRef.current = next;
+    setQueued(next);
+  }, []);
+
+  // Capture the latest `sendMessage` (returned by useChat below) so the flush
+  // helper can call the current instance from the stable `onFinish` callback.
+  const sendMessageRef = useRef<((m: { text: string }) => void) | null>(null);
+
+  // FIFO dequeue + send the next queued message (no-op when the queue is empty).
+  const flushNext = useCallback(() => {
+    const { head, rest } = dequeue(queuedRef.current);
+    if (!head) return;
+    setQueue(rest);
+    sendMessageRef.current?.({ text: head.text });
+  }, [setQueue]);
+
+  const enqueue = useCallback(
+    (text: string) => {
+      setQueue(enqueueMessage(queuedRef.current, { id: generateId(), text }));
+    },
+    [setQueue],
+  );
+  const removeQueued = useCallback(
+    (id: string) => {
+      setQueue(removeQueuedById(queuedRef.current, id));
+    },
+    [setQueue],
+  );
+
   const transport = useMemo(
     () =>
       new DefaultChatTransport<UIMessage>({
@@ -169,13 +217,24 @@ export default function ChatThread({
     id: chatStoreId,
     messages: initialMessages,
     transport,
-    onFinish: () => onTurnFinished(),
-    // In AI SDK v6 `onFinish` does NOT fire when the stream errors, so a brand
-    // new chat that fails on its first turn would never invalidate the chat list
-    // nor adopt the server-created chat id (the server still creates the row and
-    // saves the error message). Run the same post-turn path on error so the
-    // failed chat appears in history immediately instead of after a manual
-    // refresh. The error itself is still surfaced via `error` below.
+    // `onFinish` (ai@6 useChat) fires from a `finally` on EVERY terminal outcome
+    // — success, user Stop/abort (`isAbort`), network drop (`isDisconnect`), and
+    // stream error (`isError`). Keep calling `onTurnFinished()` on all of them
+    // (chat-list refresh + new-chat id adoption must happen even on a failed
+    // first turn), but flush the pending queue ONLY on a clean finish: auto-
+    // sending after the user hit Stop — or blindly retrying after a failure —
+    // would be wrong, so on Stop/disconnect/error the queue is left intact for
+    // the user to decide.
+    onFinish: ({ isAbort, isDisconnect, isError }) => {
+      onTurnFinished();
+      if (isAbort || isDisconnect || isError) return;
+      flushNext();
+    },
+    // `onError` runs in addition to `onFinish` (which ai@6 also calls on error).
+    // Log the raw failure here for devtools; the UI shows a friendly classified
+    // banner via `error` below. We still call `onTurnFinished()` (idempotent with
+    // the onFinish call) so a brand-new chat that fails its first turn is adopted
+    // and the chat list refreshes immediately rather than after a manual refresh.
     onError: (streamError) => {
       // Surface the raw failure in the browser console (devtools) for debugging;
       // the UI separately shows a friendly classified banner (see errorView).
@@ -184,6 +243,9 @@ export default function ChatThread({
     },
   });
 
+  // Keep the flush helper pointed at the latest sendMessage instance.
+  sendMessageRef.current = sendMessage;
+
   const isStreaming = status === "submitted" || status === "streaming";
 
   // Classify the turn error into a heading + detail so the banner names the cause
@@ -227,8 +289,35 @@ export default function ChatThread({
       )}
 
       <Stack gap={0} className={classes.inputWrapper}>
+        {queued.length > 0 && (
+          <Stack gap={4} className={classes.queuedList}>
+            {queued.map((m) => (
+              <Group
+                key={m.id}
+                gap={6}
+                wrap="nowrap"
+                className={classes.queuedItem}
+              >
+                <IconClockHour4 size={14} className={classes.queuedIcon} />
+                <Text size="xs" lineClamp={2} className={classes.queuedText}>
+                  {m.text}
+                </Text>
+                <ActionIcon
+                  size="xs"
+                  variant="subtle"
+                  color="gray"
+                  onClick={() => removeQueued(m.id)}
+                  aria-label={t("Remove queued message")}
+                >
+                  <IconX size={12} />
+                </ActionIcon>
+              </Group>
+            ))}
+          </Stack>
+        )}
         <ChatInput
           onSend={(text) => sendMessage({ text })}
+          onQueue={enqueue}
           onStop={stop}
           isStreaming={isStreaming}
         />

apps/client/src/features/ai-chat/utils/queue-helpers.test.ts

@@ -0,0 +1,107 @@
+import { describe, it, expect } from "vitest";
+import {
+  enqueueMessage,
+  dequeue,
+  removeQueuedById,
+  type QueuedMessage,
+} from "./queue-helpers";
+
+describe("enqueueMessage", () => {
+  it("appends a message to the end of the queue", () => {
+    const queue: QueuedMessage[] = [{ id: "a", text: "first" }];
+    const next = enqueueMessage(queue, { id: "b", text: "second" });
+    expect(next).toEqual([
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+    ]);
+  });
+
+  it("does not mutate the input queue", () => {
+    const queue: QueuedMessage[] = [{ id: "a", text: "first" }];
+    enqueueMessage(queue, { id: "b", text: "second" });
+    expect(queue).toEqual([{ id: "a", text: "first" }]);
+  });
+});
+
+describe("dequeue", () => {
+  it("returns {head:null, rest:[]} for an empty queue", () => {
+    expect(dequeue([])).toEqual({ head: null, rest: [] });
+  });
+
+  it("returns the first item as head and the remainder as rest", () => {
+    const queue: QueuedMessage[] = [
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+      { id: "c", text: "third" },
+    ];
+    const { head, rest } = dequeue(queue);
+    expect(head).toEqual({ id: "a", text: "first" });
+    expect(rest).toEqual([
+      { id: "b", text: "second" },
+      { id: "c", text: "third" },
+    ]);
+  });
+
+  it("does not mutate the input queue", () => {
+    const queue: QueuedMessage[] = [
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+    ];
+    dequeue(queue);
+    expect(queue).toEqual([
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+    ]);
+  });
+});
+
+describe("removeQueuedById", () => {
+  it("removes the matching id and leaves the others", () => {
+    const queue: QueuedMessage[] = [
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+      { id: "c", text: "third" },
+    ];
+    const next = removeQueuedById(queue, "b");
+    expect(next).toEqual([
+      { id: "a", text: "first" },
+      { id: "c", text: "third" },
+    ]);
+  });
+
+  it("returns an equivalent list when the id is not present", () => {
+    const queue: QueuedMessage[] = [{ id: "a", text: "first" }];
+    expect(removeQueuedById(queue, "missing")).toEqual([
+      { id: "a", text: "first" },
+    ]);
+  });
+
+  it("does not mutate the input queue", () => {
+    const queue: QueuedMessage[] = [
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+    ];
+    removeQueuedById(queue, "a");
+    expect(queue).toEqual([
+      { id: "a", text: "first" },
+      { id: "b", text: "second" },
+    ]);
+  });
+});
+
+describe("FIFO order", () => {
+  it("preserves order across enqueue -> dequeue", () => {
+    let queue: QueuedMessage[] = [];
+    queue = enqueueMessage(queue, { id: "1", text: "one" });
+    queue = enqueueMessage(queue, { id: "2", text: "two" });
+    queue = enqueueMessage(queue, { id: "3", text: "three" });
+
+    const order: string[] = [];
+    while (queue.length > 0) {
+      const { head, rest } = dequeue(queue);
+      if (head) order.push(head.text);
+      queue = rest;
+    }
+    expect(order).toEqual(["one", "two", "three"]);
+  });
+});

apps/client/src/features/ai-chat/utils/queue-helpers.ts

@@ -0,0 +1,34 @@
+// Pure FIFO helpers for the AI-chat "send while the agent is busy" queue.
+// Kept side-effect free so they can be unit-tested without React.
+
+export interface QueuedMessage {
+  id: string;
+  text: string;
+}
+
+/** Append a message to the end of the queue (returns a new array). */
+export function enqueueMessage(
+  queue: QueuedMessage[],
+  message: QueuedMessage,
+): QueuedMessage[] {
+  return [...queue, message];
+}
+
+/** Split the queue into its first item (`head`) and the remainder (`rest`).
+ *  `head` is null when the queue is empty. Does not mutate the input. */
+export function dequeue(queue: QueuedMessage[]): {
+  head: QueuedMessage | null;
+  rest: QueuedMessage[];
+} {
+  if (queue.length === 0) return { head: null, rest: [] };
+  const [head, ...rest] = queue;
+  return { head, rest };
+}
+
+/** Remove the queued message with the given id (returns a new array). */
+export function removeQueuedById(
+  queue: QueuedMessage[],
+  id: string,
+): QueuedMessage[] {
+  return queue.filter((m) => m.id !== id);
+}