feat(frontend): 编辑器内「润色 / 再沟通」——选段回炉 + 追加意见迭代出版本栈，接受回填

Phase 1（写作工作台重构）：编辑器选中一段即可「润色选段」，复用同步 /refine 回炉
（只读、不写库，守不变量 #3）；不满意可「再沟通」——以上一版产出为输入 + 作者新意见
再改一版，形成版本栈（useRefine，已单测）。接受回填按内容重锚落回草稿，原文已变则
提示重选、绝不盲替换（applyRefinement，已单测）。Editor 上报选区，结果以内联卡片展示。

apps/web/components/workbench/Workbench.tsx

@@ -12,11 +12,13 @@ import {
   PanelRight,
   PenLine,
   Square,
+  Wand2,
 } from "lucide-react";
 
 import { AppShell } from "@/components/AppShell";
 import { Drawer } from "@/components/Drawer";
 import { ThinkingIndicator } from "@/components/ThinkingIndicator";
+import { useToast } from "@/components/Toast";
 import { Button } from "@/components/ui/Button";
 import { SectionHeader } from "@/components/ui/SectionHeader";
 import { StatusNote } from "@/components/ui/StatusNote";
@@ -30,10 +32,12 @@ import {
   type ChapterEntry,
 } from "@/lib/workbench/chapter";
 import { composeDirective, STYLE_PRESETS } from "@/lib/workbench/directive";
+import { applyRefinement } from "@/lib/workbench/refineApply";
 import { buttonClass } from "@/lib/ui/variants";
 import { ChapterList, ChapterListContent } from "./ChapterList";
 import { ChapterAssistant, AssistantContent } from "./ChapterAssistant";
-import { Editor } from "./Editor";
+import { Editor, type EditorSelection } from "./Editor";
+import { RefinePanel } from "./RefinePanel";
 
 interface WorkbenchProps {
   project: ProjectResponse;
@@ -64,9 +68,14 @@ export function Workbench({
   // 本章指令（T4-b）：自由文本 + 风格预设 → 写本章时组装传入 draft 生成。
   const [directive, setDirective] = useState("");
   const [presetIds, setPresetIds] = useState<string[]>([]);
+  // 选区级 AI 动作（润色/再沟通）：编辑器上报的最新选区 + 结果卡开合。
+  const [selection, setSelection] = useState<EditorSelection | null>(null);
+  const [refineOpen, setRefineOpen] = useState(false);
+  const toast = useToast();
   const autosave = useAutosave(project.id, chapterNo, initialText);
   const stream = useDraftStream();
   const lastStreamText = useRef("");
+  const canRefine = selection !== null && selection.text.trim().length > 0;
   const chapterTriggerRef = useRef<HTMLButtonElement>(null);
   const assistantTriggerRef = useRef<HTMLButtonElement>(null);
 
@@ -104,6 +113,24 @@ export function Workbench({
     autosave.onChange(value);
   };
 
+  // 接受润色/再沟通产出：按内容重锚把选段替换为产出并落草稿；原文已变则提示重选（不盲替换）。
+  const onAcceptRefine = (refined: string): void => {
+    if (selection) {
+      const next = applyRefinement(text, selection.text, refined, {
+        start: selection.start,
+        end: selection.end,
+      });
+      if (next === null) {
+        toast("正文已改动，找不到原选段，请重新选择后再润色。", "error");
+      } else {
+        setText(next);
+        autosave.onChange(next);
+      }
+    }
+    setRefineOpen(false);
+    setSelection(null);
+  };
+
   // 字数统计非空白字符（与中文读者直觉一致：标点/空格不计入正文体量）。
   const wordCount = text.replace(/\s+/g, "").length;
   const closePanel = (): void => setMobilePanel(null);
@@ -153,11 +180,21 @@ export function Workbench({
             presetIds={presetIds}
             onTogglePreset={togglePreset}
           />
+          {refineOpen && canRefine && selection ? (
+            <RefinePanel
+              projectId={project.id}
+              chapterNo={chapterNo}
+              original={selection.text}
+              onAccept={onAcceptRefine}
+              onClose={() => setRefineOpen(false)}
+            />
+          ) : null}
           <div className="flex-1 overflow-auto px-6 py-8">
             <Editor
               value={text}
               onChange={onEditorChange}
               streaming={stream.isStreaming}
+              onSelectionChange={setSelection}
             />
           </div>
           <Toolbar
@@ -171,6 +208,8 @@ export function Workbench({
             liveMessage={liveMessage}
             onWrite={onWrite}
             onStop={stream.stop}
+            canRefine={canRefine}
+            onRefineSelection={() => setRefineOpen(true)}
           />
         </section>
 
@@ -358,6 +397,9 @@ interface ToolbarProps {
   liveMessage: string;
   onWrite: () => void;
   onStop: () => void;
+  // 选区级润色：有非空选区时可用；点击打开润色/再沟通结果卡。
+  canRefine: boolean;
+  onRefineSelection: () => void;
 }
 
 function Toolbar({
@@ -371,6 +413,8 @@ function Toolbar({
   liveMessage,
   onWrite,
   onStop,
+  canRefine,
+  onRefineSelection,
 }: ToolbarProps) {
   return (
     <div className="sticky bottom-0 z-10 border-t border-line bg-panel/95 px-4 py-2 backdrop-blur sm:px-6 sm:py-3">
@@ -388,6 +432,18 @@ function Toolbar({
             写本章
           </Button>
         )}
+        {!streaming ? (
+          <Button
+            onClick={onRefineSelection}
+            disabled={!canRefine}
+            variant="secondary"
+            size="sm"
+            title={canRefine ? undefined : "先在正文里选中一段再润色"}
+          >
+            <Wand2 className="h-4 w-4" aria-hidden="true" />
+            润色选段
+          </Button>
+        ) : null}
         {streaming ? (
           // ThinkingIndicator 自带 role=status，开始时播报一次「生成中」；
           // 易变字数 aria-hidden，仅供视觉，不逐 token 打扰屏读。