feat: implement multi-turn conversation system for generation record detail with deduplication enhancement

- generationRecordClient.ts: Enhance save deduplication with payload signature — replace simple recordId-based dedup with stableJsonStringify-based signature comparison; same recordId + same signature skips save, changed payload proceeds; add buildSaveSignature covering tool/mode/title/status/prompt/taskIds/assets/config/result/metadata; store signature alongside savedAt in recentlySavedRecords map for per-turn save accuracy
- EcommercePage.tsx: Introduce EcommerceHistoryTurn interface and multi-turn conversation architecture —
  - Add EcommerceHistoryTurn with full generation context (status/output/platform/market/language/ratio/requirement/images/results/counts/modules/scenes/replicateLevel); EcommerceHistoryRecord gains status/errorMessage/turns[] fields
  - beginEcommerceHistoryTurn() — start a new generation turn, create or append to record, persist to localStorage immediately
  - updateLocalEcommerceHistoryTurn() — real-time turn status sync (generating→done/failed) with record summary mirroring via syncRecordSummaryWithTurn()
  - restoreHistoryTurnInputs() — one-click parameter restoration from failed turns for retry
  - upsertCanvasNode() — insert or update canvas node by ID (dedup by turnId), alternating row layout (x: index*420, y: 0 or 160)
  - Generate flow wired to turns: status callbacks update turn state; cancel sets turn to failed; results written to turn.results
  - Record detail conversation panel refactored from single-message to per-turn iteration — each turn renders user message (requirement + meta + assets) and assistant message (status-aware text + progress bar during generation + result thumbnails); failed turns show "恢复参数" retry button; generating turn shows EcommerceProgressBar
  - openEcommerceHistoryRecord() loads all turns as canvas nodes with distributed positions; preserves generating turn tracking via activeHistoryTurnIdRef
  - History list items display status label (生成中/失败/time)
  - Product set preview backdrop moved to createPortal(document.body) with z-index 4000
- pages/ecommerce.css: Bump product-set-preview-backdrop z-index from 100 to 4000 for Portal rendering layer

src/api/generationRecordClient.ts

@@ -43,15 +43,40 @@ export interface SaveGenerationRecordResult {
 // 单个 poller 内也会重复触发。这里做客户端幂等：in-flight 合流 + 成功后短期拦截，
 // 避免后端在缺少去重时插入重复记录。
 const inFlightSaves = new Map<string, Promise<SaveGenerationRecordResult>>();
-const recentlySavedAt = new Map<string, number>();
+const recentlySavedRecords = new Map<string, { savedAt: number; signature: string }>();
 const SAVE_DEDUPE_WINDOW_MS = 60_000;
 
 function pruneRecentlySaved(now: number): void {
-  for (const [id, savedAt] of recentlySavedAt) {
-    if (now - savedAt > SAVE_DEDUPE_WINDOW_MS) recentlySavedAt.delete(id);
+  for (const [id, record] of recentlySavedRecords) {
+    if (now - record.savedAt > SAVE_DEDUPE_WINDOW_MS) recentlySavedRecords.delete(id);
   }
 }
 
+function stableJsonStringify(value: unknown): string {
+  if (value === null || typeof value !== "object") return JSON.stringify(value);
+  if (Array.isArray(value)) return `[${value.map(stableJsonStringify).join(",")}]`;
+  const entries = Object.entries(value as Record<string, unknown>)
+    .filter(([, entryValue]) => entryValue !== undefined)
+    .sort(([a], [b]) => a.localeCompare(b));
+  return `{${entries.map(([key, entryValue]) => `${JSON.stringify(key)}:${stableJsonStringify(entryValue)}`).join(",")}}`;
+}
+
+function buildSaveSignature(input: SaveGenerationRecordInput): string {
+  return stableJsonStringify({
+    tool: input.tool,
+    mode: input.mode,
+    title: input.title,
+    status: input.status,
+    prompt: input.prompt,
+    taskIds: input.taskIds,
+    assets: input.assets,
+    config: input.config,
+    result: input.result,
+    metadata: input.metadata,
+    createdAt: input.createdAt,
+  });
+}
+
 function readPendingRecords(): SaveGenerationRecordInput[] {
   try {
     const raw = window.localStorage.getItem(PENDING_RECORDS_KEY);
@@ -78,26 +103,29 @@ export async function saveGenerationRecord(input: SaveGenerationRecordInput): Pr
   pruneRecentlySaved(now);
 
   const recordId = input.clientRecordId;
+  const signature = buildSaveSignature(input);
   if (recordId) {
-    const inFlight = inFlightSaves.get(recordId);
+    const saveKey = `${recordId}:${signature}`;
+    const inFlight = inFlightSaves.get(saveKey);
     if (inFlight) return inFlight;
-    const savedAt = recentlySavedAt.get(recordId);
-    if (savedAt !== undefined && now - savedAt <= SAVE_DEDUPE_WINDOW_MS) {
-      // 终态记录只需落库一次；窗口内的重复调用直接视为已保存。
+    const savedRecord = recentlySavedRecords.get(recordId);
+    if (savedRecord && savedRecord.signature === signature && now - savedRecord.savedAt <= SAVE_DEDUPE_WINDOW_MS) {
+      // 相同 clientRecordId 且 payload 完全一致时才拦截；同一记录的多轮更新需要继续保存。
       return { source: "server", id: recordId };
     }
   }
 
   const promise = saveGenerationRecordInternal(input);
   if (recordId) {
-    inFlightSaves.set(recordId, promise);
+    const saveKey = `${recordId}:${signature}`;
+    inFlightSaves.set(saveKey, promise);
     void promise
       .then((result) => {
-        if (result.source === "server") recentlySavedAt.set(recordId, Date.now());
+        if (result.source === "server") recentlySavedRecords.set(recordId, { savedAt: Date.now(), signature });
       })
       .catch(() => undefined)
       .finally(() => {
-        inFlightSaves.delete(recordId);
+        inFlightSaves.delete(saveKey);
       });
   }
   return promise;