build-timelinelisted

# Build Timeline / 构建时间线 ## When to use / 何时使用 After A-roll and B-roll exist; before final render. Defines what plays when. A-roll/B-roll 就绪、最终渲染前。定义每一段何时播放。 ## Inputs / 输入 - `workspace/aroll/master.cues.json`. - `workspace/broll/plan.json`. - `workspace/voice/master.cues.json`. - `inputs/bgm/*.mp3` (optional). ## Output / 输出 - `workspace/timeline.json` with tracks: video(A+B), audio(voice+bgm), subtitle. ## Steps / 步骤 1. Lay A-roll on video track 1 using A-roll cues. 2. Insert B-roll on track 2 at planned start_s with picture-in-picture or full-cover style per cue. 3. Place voice on audio track 1; BGM on track 2 with ducking enabled. 4. Validate no overlap conflicts on track 1; resolve B-roll cover vs A-roll. ## Examples / 示例 ``` claude run build-timeline ``` ## Failure recovery / 失败回退 - If B-roll start > video duration, drop and log. - If A-roll missing for a span, fill with last B-roll frame frozen.