fix: Step2素材选择后调用后端/clips/from-assets接口，支持required_clips_count

问题：前端在本地构建clips（每素材1个片段，start_time=0），
未调用后端/clips/from-assets，导致：
- 模板要求4个片段但只选了3个素材时只生成3个片段
- 后端随机start_time和多片段逻辑从未被触发
- 片段时间段固定从0开始，不随机

修复：
1. createClipsFromAssets增加requiredClipsCount可选参数
2. useStep2Materials改为：先PUT /clips清空旧片段，
   再POST /clips/from-assets创建片段，传入required_clips_count=模板segments数
3. 删除已废弃的buildClipsFromAssets工具函数（无其他引用）

后端/clips/from-assets自动处理：
- 素材不够时同一素材切多个片段
- 随机start_time，不重复
- 保证片段数=required_clips_count

apps/web/src/api/template-editor/clips.ts

@@ -90,10 +90,18 @@ export async function createClipsFromAssets(
   templateId: string,
   assetIds: string[],
   clipType = "main",
+  requiredClipsCount?: number,
 ): Promise<ClipsFromAssetsResponse> {
+  const body: Record<string, unknown> = {
+    asset_ids: assetIds,
+    clip_type: clipType,
+  }
+  if (requiredClipsCount !== undefined) {
+    body.required_clips_count = requiredClipsCount
+  }
   const response = await apiClient.post<ClipsFromAssetsResponse>(
     `/templates/${templateId}/editor/clips/from-assets`,
-    { asset_ids: assetIds, clip_type: clipType },
+    body,
   )
   return response.data
 }

apps/web/src/pages/generate/hooks/useStep2Materials.ts

@@ -3,11 +3,9 @@
  * 组合素材库加载 + 智能匹配两个子 Hook
  */
 import { useCallback, useEffect, useRef } from "react"
-import type { AssetItem } from "@/api/assets"
 import type { TemplateSegment } from "@/api/templates/types"
-import { updateEditPlanClips } from "@/api/template-editor"
+import { updateEditPlanClips, createClipsFromAssets } from "@/api/template-editor"
 import { formatDuration } from "../utils/formatDuration"
-import { buildClipsFromAssets } from "../utils/buildClipsFromAssets"
 import { useMaterialLibrary } from "./step2-materials/useMaterialLibrary"
 import { useSmartMatch } from "./step2-materials/useSmartMatch"
 import { useDraftAutoSave } from "./useDraftAutoSave"
@@ -72,17 +70,19 @@ export function useStep2Materials({
     scheduleSave({ asset_ids: ids }, 500)
   }, [selectedTemplate, materialMode, selectedMaterials, smartSelectedIds, scheduleSave])
 
-  /* ── Step2 选择素材后同步写入 edit_plan_clips（防抖 800ms，失败静默） ── */
+  /* ── Step2 选择素材后同步写入 edit_plan_clips（防抖 800ms，失败静默） ──
+   * 调用后端 POST /clips/from-assets，由后端处理：
+   *   - 素材不够时同一素材切多个片段
+   *   - 随机 start_time，不重复
+   *   - required_clips_count 保证片段数与模板 segments 一致
+   * 先 PUT /clips（空数组）清空旧片段，再调用 from-assets 创建新片段
+   */
   const clipsTimerRef = useRef<ReturnType<typeof setTimeout>>()
   const clipsAbortRef = useRef<AbortController | null>(null)
   const templateSegmentsRef = useRef(templateSegments)
   templateSegmentsRef.current = templateSegments
   const selectedTemplateRef = useRef(selectedTemplate)
   selectedTemplateRef.current = selectedTemplate
-  const materialsRef = useRef(materials)
-  materialsRef.current = materials
-  const smartMatchedRef = useRef<AssetItem[]>(smartMatch.smartMatchedResults)
-  smartMatchedRef.current = smartMatch.smartMatchedResults
 
   useEffect(() => {
     const tid = selectedTemplateRef.current
@@ -97,15 +97,14 @@ export function useStep2Materials({
       const controller = new AbortController()
       clipsAbortRef.current = controller
 
-      const clips = buildClipsFromAssets({
-        selectedIds: ids,
-        materials: materialsRef.current.items,
-        smartMatchedAssets: smartMatchedRef.current,
-        templateSegments: templateSegmentsRef.current || [],
-      })
+      const segs = templateSegmentsRef.current || []
+      const requiredClipsCount = segs.length > 0 ? segs.length : undefined
 
       try {
-        await updateEditPlanClips(tid, clips, controller.signal)
+        // 1. 清空旧片段
+        await updateEditPlanClips(tid, [], controller.signal)
+        // 2. 调用后端 from-assets 接口创建片段
+        await createClipsFromAssets(tid, ids, "main", requiredClipsCount)
       } catch (err) {
         const name = (err as { name?: string })?.name
         if (name !== "CanceledError" && name !== "AbortError") {

apps/web/src/pages/generate/utils/buildClipsFromAssets.ts

@@ -1,69 +0,0 @@
-/**
- * 将选中素材 + 模板 segments 构建为 edit_plan_clips 写入数据。
- *
- * 逻辑必须与 FrontendPreviewPlayer.tsx 中 buildPlaybackSegments 完全一致：
- *   assetDuration = asset.duration || asset.metadata?.duration || 30
- *   tplSeg = templateSegments[i] || lastSegment
- *   segDuration = clamp(assetDuration, tplSeg.duration_min, tplSeg.duration_max)
- *   start_time = 0
- *   // 关键：预览播放器中 endTime = min(startTime + segDuration, assetDuration)
- *   // 因此 clips.duration 也必须用 min(segDuration, assetDuration) 截断，
- *   // 避免素材实际时长比 clamp 后的 segDuration 短时，Worker 尝试读取不存在的片段
- *   duration = min(segDuration, assetDuration)
- *
- * 预览播放器（Canvas 实时预览）直接在内存中构建 segments 播放，不读 edit_plan_clips；
- * 本函数产出的 clips 写入 DB 后由 Worker 渲染。两边用完全相同的时长计算，
- * 保证用户在编辑过程中看到的预览与最终生成视频一致。
- */
-import type { AssetItem } from "@/api/assets"
-import type { TemplateSegment } from "@/api/templates/types"
-import type { EditPlanClipInput } from "@/api/template-editor"
-
-interface BuildClipsOptions {
-  /** 选中的素材 ID 列表（按选择顺序） */
-  selectedIds: string[]
-  /** 已加载的素材列表（用于查 duration） */
-  materials: AssetItem[]
-  /** 智能匹配返回的素材（auto 模式下可能不在 materials 列表中） */
-  smartMatchedAssets?: AssetItem[]
-  /** 模板 segments */
-  templateSegments?: TemplateSegment[]
-}
-
-export function buildClipsFromAssets({
-  selectedIds,
-  materials,
-  smartMatchedAssets = [],
-  templateSegments = [],
-}: BuildClipsOptions): EditPlanClipInput[] {
-  if (!selectedIds.length) return []
-
-  // 合并两个素材来源，建立 id → asset 索引
-  const assetMap = new Map<string, AssetItem>()
-  for (const a of materials) assetMap.set(a.id, a)
-  for (const a of smartMatchedAssets) assetMap.set(a.id, a)
-
-  const lastSeg = templateSegments[templateSegments.length - 1]
-
-  return selectedIds.map((assetId, i) => {
-    const asset = assetMap.get(assetId)
-    const assetDuration = asset?.duration || asset?.metadata?.duration || 30
-
-    const tplSeg = templateSegments[i] || lastSeg
-    const segDuration = tplSeg
-      ? Math.min(tplSeg.duration_max, Math.max(tplSeg.duration_min, assetDuration))
-      : Math.min(assetDuration, 10)
-
-    // 与 FrontendPreviewPlayer.buildPlaybackSegments 中
-    //   endTime = Math.min(startTime + segDuration, assetDuration)
-    // 保持一致：duration 不能超过素材实际时长
-    const duration = Math.min(segDuration, assetDuration)
-
-    return {
-      asset_id: assetId,
-      start_time: 0,
-      duration,
-      order: i,
-    }
-  })
-}