fix: preserve custom system prompt on template switch & render SVG preview in history

frontend/src/lib/api.ts

@@ -103,4 +103,5 @@ export const api = {
   listHistory: (limit = 50) => req<GenerationRecord[]>(`/api/history?limit=${limit}`),
   clearHistory: () => req<void>("/api/history", { method: "DELETE" }),
   deleteHistory: (id: number) => req<void>(`/api/history/${id}`, { method: "DELETE" }),
+  getGenerationSvg: (id: number) => req<{ svg: string }>(`/api/history/${id}/svg`),
 };

frontend/src/pages/Generate.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useRef, useState } from "react";
+import { useEffect, useMemo, useRef, useState, useCallback } from "react";
 import CodeMirror from "@uiw/react-codemirror";
 import { python } from "@codemirror/lang-python";
 import { vscodeDark } from "@uiw/codemirror-theme-vscode";
@@ -24,6 +24,7 @@ export default function GeneratePage() {
   const [showDiff, setShowDiff] = useState(false);
   const svgRef = useRef<HTMLDivElement>(null);
   const abortRef = useRef<AbortController | null>(null);
+  const userModifiedRef = useRef(false); // 追踪用户是否手动修改了 systemOverride
 
   useEffect(() => {
     return () => {
@@ -49,17 +50,23 @@ export default function GeneratePage() {
   // 当用户选择模板，把 user_template 灌入编辑框
   const tpl = useMemo(() => templates.find((t) => t.id === templateId) || null, [templates, templateId]);
   useEffect(() => {
+    // 切换模板时重置用户修改标记
+    userModifiedRef.current = false;
     if (tpl?.user_template && !userPrompt) {
       setUserPrompt(tpl.user_template);
     }
-    if (tpl?.system_prompt) setSystemOverride(tpl.system_prompt);
+    // 仅在用户未手动修改时，才将 systemOverride 同步为模板默认值
+    if (tpl?.system_prompt && !userModifiedRef.current) {
+      setSystemOverride(tpl.system_prompt);
+    }
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [templateId]);
 
-  // 模板切换时刷新 systemOverride（当用户没自定义时跟模板走）
-  useEffect(() => {
-    if (tpl) setSystemOverride(tpl.system_prompt || "");
-  }, [tpl]);
+  // 用户手动编辑 systemOverride 时标记为已修改
+  const handleSystemOverrideChange = useCallback((value: string) => {
+    userModifiedRef.current = true;
+    setSystemOverride(value);
+  }, []);
 
   async function run() {
     if (!modelId) {
@@ -219,7 +226,7 @@ export default function GeneratePage() {
                 rows={5}
                 className="w-full input font-mono text-xs mt-2"
                 value={systemOverride}
-                onChange={(e) => setSystemOverride(e.target.value)}
+                onChange={(e) => handleSystemOverrideChange(e.target.value)}
                 placeholder="留空则使用后端默认科研绘图约束；选择模板时默认填入模板的 system_prompt"
               />
             )}

frontend/src/pages/History.tsx

@@ -9,6 +9,9 @@ export default function HistoryPage() {
   const [items, setItems] = useState<GenerationRecord[]>([]);
   const [active, setActive] = useState<GenerationRecord | null>(null);
   const [msg, setMsg] = useState("");
+  const [svgContent, setSvgContent] = useState<string | null>(null);
+  const [svgLoading, setSvgLoading] = useState(false);
+  const [svgError, setSvgError] = useState("");
 
   async function load() {
     try {
@@ -21,16 +24,33 @@ export default function HistoryPage() {
     load();
   }, []);
 
+  async function selectRecord(r: GenerationRecord) {
+    setActive(r);
+    setSvgContent(null);
+    setSvgError("");
+    setSvgLoading(true);
+    try {
+      const result = await api.getGenerationSvg(r.id);
+      setSvgContent(result.svg || null);
+    } catch (e) {
+      setSvgError("SVG 加载失败：" + (e as Error).message);
+    } finally {
+      setSvgLoading(false);
+    }
+  }
+
   async function clearAll() {
     if (!confirm("清空全部历史？")) return;
     await api.clearHistory();
     setItems([]);
     setActive(null);
+    setSvgContent(null);
   }
 
   async function remove(id: number) {
     await api.deleteHistory(id);
     setActive(null);
+    setSvgContent(null);
     await load();
   }
 
@@ -52,7 +72,7 @@ export default function HistoryPage() {
             items.map((r) => (
               <li
                 key={r.id}
-                onClick={() => setActive(r)}
+                onClick={() => selectRecord(r)}
                 className={`p-3 border rounded cursor-pointer text-sm ${
                   active?.id === r.id ? "bg-slate-100 border-slate-400" : "hover:bg-slate-50"
                 }`}
@@ -104,6 +124,27 @@ export default function HistoryPage() {
                 editable={false}
               />
             </div>
+            <div className="bg-white border border-slate-200 rounded-lg p-4">
+              <div className="flex items-center justify-between mb-2">
+                <div className="font-semibold text-sm">SVG 预览</div>
+              </div>
+              {svgError && (
+                <div className="text-sm text-rose-600 bg-rose-50 border border-rose-200 rounded p-2 mb-2">{svgError}</div>
+              )}
+              <div className="border border-slate-200 rounded bg-slate-50 flex items-center justify-center min-h-[320px] p-3">
+                {svgLoading ? (
+                  <div className="text-slate-400 text-sm">SVG 加载中…</div>
+                ) : svgContent ? (
+                  <div
+                    className="w-full h-full flex items-center justify-center"
+                    dangerouslySetInnerHTML={{ __html: svgContent }}
+                    style={{ maxHeight: "70vh" }}
+                  />
+                ) : (
+                  <div className="text-slate-400 text-sm">暂无 SVG 内容</div>
+                )}
+              </div>
+            </div>
           </div>
         ) : (
           <div className="text-slate-500 text-sm">点击左侧查看详情。</div>