feat: 支持删除单条聊天消息（用户提问与模型回答）

- 后端新增 DELETE /api/threads/{thread_id}/messages/{message_id}，从最新 checkpoint 的 messages 通道过滤掉指定 id 并写回新 checkpoint
- 前端 useDeleteMessage 钩子 + DeleteMessageButton（带确认框）组件
- 在用户问题气泡与助手回答工具栏上各加删除按钮，仅对已落库消息显示
- MessageList 本地隐藏已删消息并在切换会话时重置；只读/分享场景禁用删除
- 新增 deleteMessage 相关中英文案

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend-web/src/components/workspace/messages/delete-message-button.tsx

@@ -0,0 +1,95 @@
+import { Trash2Icon } from "lucide-react";
+import { useState } from "react";
+import { toast } from "sonner";
+
+import { Button } from "@/components/ui/button";
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
+import { useI18n } from "@/core/i18n/hooks";
+import { useDeleteMessage } from "@/core/threads/hooks";
+
+import { Tooltip } from "../tooltip";
+
+/**
+ * Hover affordance that deletes a single message (a user question or an
+ * assistant answer) after a confirmation step. The actual removal is persisted
+ * server-side; `onDeleted` lets the parent hide the bubble immediately without
+ * waiting for the stream cache to refresh.
+ */
+export function DeleteMessageButton({
+  threadId,
+  messageId,
+  onDeleted,
+  className,
+}: {
+  threadId: string;
+  messageId: string;
+  onDeleted?: () => void;
+  className?: string;
+}) {
+  const { t } = useI18n();
+  const [open, setOpen] = useState(false);
+  const deleteMessage = useDeleteMessage();
+
+  const handleConfirm = async () => {
+    try {
+      await deleteMessage.mutateAsync({ threadId, messageId });
+      onDeleted?.();
+      setOpen(false);
+    } catch (error) {
+      toast.error(
+        error instanceof Error ? error.message : "删除消息失败。",
+      );
+    }
+  };
+
+  return (
+    <>
+      <Tooltip content={t.inputBox.deleteMessage}>
+        <Button
+          size="icon-sm"
+          type="button"
+          variant="ghost"
+          className={className}
+          onClick={() => setOpen(true)}
+        >
+          <Trash2Icon size={12} />
+        </Button>
+      </Tooltip>
+      <Dialog open={open} onOpenChange={setOpen}>
+        <DialogContent className="sm:max-w-sm">
+          <DialogHeader>
+            <DialogTitle>{t.inputBox.deleteMessageConfirmTitle}</DialogTitle>
+            <DialogDescription>
+              {t.inputBox.deleteMessageConfirmDescription}
+            </DialogDescription>
+          </DialogHeader>
+          <DialogFooter>
+            <Button
+              type="button"
+              variant="ghost"
+              onClick={() => setOpen(false)}
+              disabled={deleteMessage.isPending}
+            >
+              {t.common.cancel}
+            </Button>
+            <Button
+              type="button"
+              variant="destructive"
+              onClick={() => void handleConfirm()}
+              disabled={deleteMessage.isPending}
+            >
+              {t.common.delete}
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
+    </>
+  );
+}

frontend-web/src/components/workspace/messages/message-list-item.tsx

@@ -57,6 +57,7 @@ import { CopyButton } from '../copy-button';
 import { Tooltip } from '../tooltip';
 import { SkillDisplayBlock } from '../skill-display-block';
 import { ThreadContext } from './context';
+import { DeleteMessageButton } from './delete-message-button';
 import { DownloadWordButton } from './download-word-button';
 import { MarkdownContent, type MarkdownContentProps } from './markdown-content';
 import { MessageTokenUsage } from './message-token-usage';
@@ -135,6 +136,7 @@ export function MessageListItem({
   displaySources = [],
   extraRehypePlugins,
   onEditResubmit,
+  onMessageDeleted,
 }: {
   className?: string;
   fitRowToContent?: boolean;
@@ -145,12 +147,18 @@ export function MessageListItem({
   displaySources?: RuntimeDisplaySource[];
   extraRehypePlugins?: ReturnType<typeof useRehypeSplitWordsIntoSpans>;
   onEditResubmit?: (text: string) => void;
+  onMessageDeleted?: (messageId: string) => void;
 }) {
   const isHuman = message.type === 'human';
   const messageMarkdown =
     extractContentFromMessage(message) ??
     extractReasoningContentFromMessage(message) ??
     '';
+  // Deletion is offered only for messages that already exist server-side
+  // (real, non-optimistic ids). Optimistic placeholders (`opt-*`) have no
+  // checkpoint entry to remove.
+  const canDelete =
+    !!onMessageDeleted && !!message.id && !message.id.startsWith('opt-');
   return (
     <AIElementMessage
       className={cn(
@@ -170,6 +178,7 @@ export function MessageListItem({
         displaySources={displaySources}
         extraRehypePlugins={extraRehypePlugins}
         onEditResubmit={onEditResubmit}
+        onMessageDeleted={onMessageDeleted}
       />
       {/*
         Human messages carry their own inline copy/edit toolbar inside
@@ -191,6 +200,13 @@ export function MessageListItem({
                 fileName="message"
               />
             )}
+            {canDelete && (
+              <DeleteMessageButton
+                threadId={threadId}
+                messageId={message.id!}
+                onDeleted={() => onMessageDeleted?.(message.id!)}
+              />
+            )}
           </div>
         </MessageToolbar>
       )}
@@ -214,6 +230,7 @@ function HumanMessageBlock({
   messageTime,
   components,
   onEditResubmit,
+  deleteButton,
 }: {
   text: string;
   pageContext?: EmbeddedPageContext | null;
@@ -221,6 +238,7 @@ function HumanMessageBlock({
   messageTime: { label: string; full: string } | null;
   components: MarkdownContentProps["components"];
   onEditResubmit?: (text: string) => void;
+  deleteButton?: React.ReactNode;
 }) {
   const { t } = useI18n();
   const [editing, setEditing] = useState(false);
@@ -298,10 +316,10 @@ function HumanMessageBlock({
       )}
       <MessageTimeStamp time={messageTime} align="right" />
       {pageContext && <EmbeddedPageContextCard pageContext={pageContext} />}
-      {text && (
+      {(text || deleteButton) && (
         <div className="flex items-center gap-0.5 opacity-0 transition-opacity duration-200 group-hover/conversation-message:opacity-100">
-          <CopyButton clipboardData={text} className="size-6" />
-          {onEditResubmit && (
+          {text && <CopyButton clipboardData={text} className="size-6" />}
+          {text && onEditResubmit && (
             <Tooltip content={t.inputBox.editQuestion}>
               <Button
                 size="icon-sm"
@@ -314,6 +332,7 @@ function HumanMessageBlock({
               </Button>
             </Tooltip>
           )}
+          {deleteButton}
         </div>
       )}
     </div>
@@ -360,6 +379,7 @@ function MessageContent_({
   displaySources = [],
   extraRehypePlugins,
   onEditResubmit,
+  onMessageDeleted,
 }: {
   className?: string;
   message: Message;
@@ -369,6 +389,7 @@ function MessageContent_({
   displaySources?: RuntimeDisplaySource[];
   extraRehypePlugins?: ReturnType<typeof useRehypeSplitWordsIntoSpans>;
   onEditResubmit?: (text: string) => void;
+  onMessageDeleted?: (messageId: string) => void;
 }) {
   const baseRehypePlugins = useRehypeSplitWordsIntoSpans(isLoading);
 
@@ -500,6 +521,8 @@ function MessageContent_({
   }
 
   if (isHuman) {
+    const canDelete =
+      !!onMessageDeleted && !!message.id && !message.id.startsWith('opt-');
     return (
       <HumanMessageBlock
         text={parsedHumanContent.content}
@@ -508,6 +531,16 @@ function MessageContent_({
         messageTime={messageTime}
         components={components}
         onEditResubmit={onEditResubmit}
+        deleteButton={
+          canDelete ? (
+            <DeleteMessageButton
+              threadId={threadId}
+              messageId={message.id!}
+              onDeleted={() => onMessageDeleted?.(message.id!)}
+              className="size-6"
+            />
+          ) : null
+        }
       />
     );
   }

frontend-web/src/components/workspace/messages/message-list.tsx

@@ -1,7 +1,7 @@
 import type { Message } from "@langchain/langgraph-sdk";
 import type { BaseStream } from "@langchain/langgraph-sdk/react";
 import { CheckIcon, SendIcon, XIcon } from "lucide-react";
-import { useCallback, useEffect, useMemo, useState } from "react";
+import { useCallback, useContext, useEffect, useMemo, useState } from "react";
 
 import {
   Conversation,
@@ -37,6 +37,7 @@ import { resolveAllowMultiple } from "@/roundtable-planning/lib/clarification";
 import { ArtifactFileList } from "../artifacts/artifact-file-list";
 import { StreamingIndicator } from "../streaming-indicator";
 
+import { ThreadContext } from "./context";
 import { MarkdownContent } from "./markdown-content";
 import { MessageGroup } from "./message-group";
 import { MessageListItem } from "./message-list-item";
@@ -88,7 +89,37 @@ export function MessageList({
   );
   const updateSubtask = useUpdateSubtask();
   const { t } = useI18n();
-  const messages = thread.messages;
+  const threadContext = useContext(ThreadContext);
+  // Read-only contexts (public share, mock previews) must not offer deletion.
+  const allowDelete = !threadContext?.publicShareCode && !threadContext?.isMock;
+
+  // Locally hide messages the user just deleted. The server-side checkpoint is
+  // trimmed immediately, but the live `useStream` cache still holds the message
+  // until the next refetch — filtering by id here makes the removal instant and
+  // keeps it hidden for the rest of the session (a reload reads the trimmed
+  // state). Reset whenever the active thread changes.
+  const [hiddenMessageIds, setHiddenMessageIds] = useState<Set<string>>(
+    () => new Set(),
+  );
+  useEffect(() => {
+    setHiddenMessageIds(new Set());
+  }, [threadId]);
+  const handleMessageDeleted = useCallback((messageId: string) => {
+    setHiddenMessageIds((prev) => {
+      const next = new Set(prev);
+      next.add(messageId);
+      return next;
+    });
+  }, []);
+
+  const allMessages = thread.messages;
+  const messages = useMemo(
+    () =>
+      hiddenMessageIds.size === 0
+        ? allMessages
+        : allMessages.filter((m) => !m.id || !hiddenMessageIds.has(m.id)),
+    [allMessages, hiddenMessageIds],
+  );
 
   // Stamp a wall-clock time onto every question/answer the first time it is
   // seen, in a single batched commit. Questions sent this session already carry
@@ -259,6 +290,9 @@ export function MessageList({
                   displaySources={displaySources}
                   extraRehypePlugins={extraRehypePlugins}
                   onEditResubmit={onEditResubmit}
+                  onMessageDeleted={
+                    allowDelete ? handleMessageDeleted : undefined
+                  }
                 />
               );
             });