feat(ai写作): 历史回看右侧成稿可编辑并保存回历史记录

- 后端新增 PUT /api/ai-writing/sessions/{id}/draft（属主校验，draft_title 可选）
- 前端历史模式放开只读，工具栏新增「保存」按钮持久化修改
- 实时写作完成态保持原样（仅导出，不落库）

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

frontend-web/src/open-canvas/api/ai-writing-sessions.ts

@@ -82,6 +82,27 @@ export async function renameAIWritingSession(id: string, title: string): Promise
   return resp.json();
 }
 
+/**
+ * 更新历史会话的成稿正文（历史回看时用户在右侧编辑器里直接修改并保存）。
+ * draftTitle 省略时后端不动原标题。
+ */
+export async function updateAIWritingDraft(
+  id: string,
+  draftMarkdown: string,
+  draftTitle?: string,
+): Promise<AIWritingSessionSummary> {
+  const resp = await apiFetch(`${BASE()}/${id}/draft`, {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({
+      draft_markdown: draftMarkdown,
+      ...(draftTitle === undefined ? {} : { draft_title: draftTitle }),
+    }),
+  });
+  if (!resp.ok) throw new Error(`保存修改失败: ${resp.status}`);
+  return resp.json();
+}
+
 export async function deleteAIWritingSession(id: string): Promise<void> {
   const resp = await apiFetch(`${BASE()}/${id}`, { method: 'DELETE' });
   if (!resp.ok) throw new Error(`删除失败: ${resp.status}`);

frontend-web/src/open-canvas/components/ai-writing/AIWritingDraftPanel.tsx

@@ -102,7 +102,8 @@ export function AIWritingDraftPanel() {
           <TextArtifactRenderer
             content={textContent}
             isStreaming={!showCompletedDraftView}
-            readOnly={isHistoryMode}
+            readOnly={false}
+            onSaveDraft={isHistoryMode ? history?.saveHistoryDraft : undefined}
           />
         </div>
       </div>

frontend-web/src/open-canvas/components/artifact/TextArtifactRenderer.tsx

@@ -24,6 +24,8 @@ interface TextArtifactRendererProps {
   isStreaming?: boolean;
   /** 完成态只读（如历史回看）：保留目录 + 排版，禁用编辑与 AI 润色 */
   readOnly?: boolean;
+  /** 历史回看可编辑场景：提供后工具栏出现「保存」按钮，把修改持久化回会话 */
+  onSaveDraft?: (markdown: string, title?: string) => Promise<void>;
 }
 
 interface PanelPos {
@@ -40,7 +42,7 @@ interface LastAction {
   customInstruction?: string;
 }
 
-export function TextArtifactRenderer({ content, isStreaming, readOnly = false }: TextArtifactRendererProps) {
+export function TextArtifactRenderer({ content, isStreaming, readOnly = false, onSaveDraft }: TextArtifactRendererProps) {
   const { artifact, setArtifact } = useCanvasGraphContext();
   const { writingSelection } = useCanvasUIContext();
 
@@ -280,6 +282,7 @@ export function TextArtifactRenderer({ content, isStreaming, readOnly = false }:
         markdown={content.fullMarkdown}
         title={content.title}
         readOnly={readOnly}
+        onSave={onSaveDraft}
       />
 
       <div className="flex-1 flex min-h-0 overflow-hidden">

frontend-web/src/open-canvas/components/artifact/WritingToolbar.tsx

@@ -14,6 +14,7 @@ import {
   Pilcrow,
   Download,
   Loader2,
+  Save,
 } from "lucide-react";
 import { useState } from "react";
 import { toast } from "sonner";
@@ -71,14 +72,32 @@ interface WritingToolbarProps {
   title?: string;
   /** 历史回看等场景：仅保留导出，隐藏格式工具 */
   readOnly?: boolean;
+  /** 提供后显示「保存」按钮，把当前正文持久化（历史回看可编辑场景） */
+  onSave?: (markdown: string, title?: string) => Promise<void>;
 }
 
-export function WritingToolbar({ editor, markdown, title, readOnly = false }: WritingToolbarProps) {
+export function WritingToolbar({ editor, markdown, title, readOnly = false, onSave }: WritingToolbarProps) {
   const [exporting, setExporting] = useState(false);
+  const [saving, setSaving] = useState(false);
 
   if (!editor) return null;
 
   const canExport = !exporting && !!markdown?.trim();
+  const canSave = !!onSave && !saving && !!markdown?.trim();
+
+  const handleSave = async () => {
+    if (!onSave || saving || !markdown?.trim()) return;
+    setSaving(true);
+    try {
+      await onSave(markdown, title);
+      toast.success("已保存修改");
+    } catch (err) {
+      console.error("[writing-save] failed", err);
+      toast.error("保存失败,请稍后重试");
+    } finally {
+      setSaving(false);
+    }
+  };
 
   const handleExport = async () => {
     if (!canExport) return;
@@ -240,8 +259,40 @@ export function WritingToolbar({ editor, markdown, title, readOnly = false }: Wr
         <Strikethrough className="h-3.5 w-3.5" />
       </ToolbarButton>
 
-      {/* Right side: export + model selector */}
+      {/* Right side: save + export + model selector */}
       <div className="ml-auto flex items-center gap-1">
+        {onSave && (
+          <>
+            <Tooltip>
+              <TooltipTrigger asChild>
+                <button
+                  type="button"
+                  onMouseDown={(e) => {
+                    e.preventDefault();
+                    void handleSave();
+                  }}
+                  disabled={!canSave}
+                  className={cn(
+                    "inline-flex h-7 items-center justify-center gap-1 rounded-md px-2 text-xs font-medium transition-colors",
+                    "bg-primary text-primary-foreground hover:bg-primary/90",
+                    "disabled:pointer-events-none disabled:opacity-40",
+                  )}
+                >
+                  {saving ? (
+                    <Loader2 className="h-3.5 w-3.5 animate-spin" />
+                  ) : (
+                    <Save className="h-3.5 w-3.5" />
+                  )}
+                  保存
+                </button>
+              </TooltipTrigger>
+              <TooltipContent side="bottom" className="text-xs">
+                保存修改到历史记录
+              </TooltipContent>
+            </Tooltip>
+            <Separator orientation="vertical" className="mx-0.5 h-4" />
+          </>
+        )}
         <Tooltip>
           <TooltipTrigger asChild>
             <button

frontend-web/src/open-canvas/contexts/AIWritingHistoryContext.tsx

@@ -1,6 +1,6 @@
 import { createContext, useCallback, useContext, useMemo, useState, type ReactNode } from 'react';
 
-import { getAIWritingSession } from '../api/ai-writing-sessions';
+import { getAIWritingSession, updateAIWritingDraft } from '../api/ai-writing-sessions';
 import type { AIWritingSessionSummary } from '../api/ai-writing-sessions';
 import { useCanvasGraphContext } from './CanvasGraphContext';
 import { useCanvasUIContext } from './CanvasUIContext';
@@ -10,6 +10,8 @@ type AIWritingHistoryContextValue = {
   isHistoryMode: boolean;
   openHistory: (session: AIWritingSessionSummary) => Promise<void>;
   closeHistory: () => void;
+  /** 历史回看时把用户修改后的正文保存回该会话（持久化到后端）。 */
+  saveHistoryDraft: (markdown: string, title?: string) => Promise<void>;
 };
 
 const AIWritingHistoryContext = createContext<AIWritingHistoryContextValue | null>(null);
@@ -52,14 +54,25 @@ export function AIWritingHistoryProvider({ children }: { children: ReactNode })
     setIsDraftEditable(true);
   }, [setArtifact, setIsDraftEditable]);
 
+  const saveHistoryDraft = useCallback(
+    async (markdown: string, title?: string) => {
+      if (!historySession) return;
+      const updated = await updateAIWritingDraft(historySession.id, markdown, title);
+      // 回写本地会话，保证后续重开/重命名读到最新成稿
+      setHistorySession((prev) => (prev && prev.id === updated.id ? updated : prev));
+    },
+    [historySession],
+  );
+
   const value = useMemo(
     () => ({
       historySession,
       isHistoryMode: historySession !== null,
       openHistory,
       closeHistory,
+      saveHistoryDraft,
     }),
-    [historySession, openHistory, closeHistory],
+    [historySession, openHistory, closeHistory, saveHistoryDraft],
   );
 
   return (