v0.15: Live Photo 生产规则 — 平台限制、拼图版式、长视频处理、发布提醒、可见文案规则

新增 Live Photo 正式能力：单视频、二宫格、三宫格、四宫格、三连拼图、
长视频低成本诊断。增加 references/live-photo-production.md 生产规范、
scripts/ 工具链（contact sheet / .pvt 打包 / Apple metadata）、
validator R8 visual bounds + R9 title gap、文档约束测试。

由 Codex 完成主体实现。

scripts/add-livephoto-mov-metadata.swift

@@ -0,0 +1,140 @@
+import Foundation
+import AVFoundation
+import CoreMedia
+
+guard CommandLine.arguments.count == 4 else {
+    fputs("Usage: swift add-livephoto-mov-metadata.swift <input.mov> <output.mov> <asset-id>\n", stderr)
+    exit(2)
+}
+
+let inputURL = URL(fileURLWithPath: CommandLine.arguments[1])
+let outputURL = URL(fileURLWithPath: CommandLine.arguments[2])
+let assetIdentifier = CommandLine.arguments[3]
+
+try? FileManager.default.removeItem(at: outputURL)
+
+func quickTimeMetadataItem(key: String, value: NSCopying & NSObjectProtocol, dataType: String) -> AVMutableMetadataItem {
+    let item = AVMutableMetadataItem()
+    item.keySpace = .quickTimeMetadata
+    item.key = key as NSString
+    item.value = value
+    item.dataType = dataType
+    return item
+}
+
+let asset = AVURLAsset(url: inputURL)
+let semaphore = DispatchSemaphore(value: 0)
+var didFail = false
+
+Task {
+    do {
+        let tracks = try await asset.loadTracks(withMediaType: .video)
+        guard let videoTrack = tracks.first else {
+            throw NSError(domain: "LivePhotoMetadata", code: 1, userInfo: [NSLocalizedDescriptionKey: "No video track"])
+        }
+
+        let reader = try AVAssetReader(asset: asset)
+        let readerOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: nil)
+        readerOutput.alwaysCopiesSampleData = false
+        guard reader.canAdd(readerOutput) else {
+            throw NSError(domain: "LivePhotoMetadata", code: 2, userInfo: [NSLocalizedDescriptionKey: "Cannot add reader output"])
+        }
+        reader.add(readerOutput)
+
+        let writer = try AVAssetWriter(outputURL: outputURL, fileType: .mov)
+        let formatDescriptions = try await videoTrack.load(.formatDescriptions)
+        let sourceFormatHint = formatDescriptions.first
+        let writerInput = AVAssetWriterInput(mediaType: .video, outputSettings: nil, sourceFormatHint: sourceFormatHint)
+        writerInput.expectsMediaDataInRealTime = false
+        guard writer.canAdd(writerInput) else {
+            throw NSError(domain: "LivePhotoMetadata", code: 3, userInfo: [NSLocalizedDescriptionKey: "Cannot add writer input"])
+        }
+        writer.add(writerInput)
+
+        let contentIdentifier = quickTimeMetadataItem(
+            key: "com.apple.quicktime.content.identifier",
+            value: assetIdentifier as NSString,
+            dataType: "com.apple.metadata.datatype.UTF-8"
+        )
+        writer.metadata = [contentIdentifier]
+
+        let metadataSpec: [String: Any] = [
+            kCMMetadataFormatDescriptionMetadataSpecificationKey_Identifier as String: "mdta/com.apple.quicktime.still-image-time",
+            kCMMetadataFormatDescriptionMetadataSpecificationKey_DataType as String: "com.apple.metadata.datatype.int8"
+        ]
+        var metadataDescription: CMFormatDescription?
+        let status = CMMetadataFormatDescriptionCreateWithMetadataSpecifications(
+            allocator: kCFAllocatorDefault,
+            metadataType: kCMMetadataFormatType_Boxed,
+            metadataSpecifications: [metadataSpec] as CFArray,
+            formatDescriptionOut: &metadataDescription
+        )
+        guard status == noErr, let metadataDescription else {
+            throw NSError(domain: "LivePhotoMetadata", code: 4, userInfo: [NSLocalizedDescriptionKey: "Cannot create metadata description"])
+        }
+
+        let metadataInput = AVAssetWriterInput(mediaType: .metadata, outputSettings: nil, sourceFormatHint: metadataDescription)
+        let metadataAdaptor = AVAssetWriterInputMetadataAdaptor(assetWriterInput: metadataInput)
+        guard writer.canAdd(metadataInput) else {
+            throw NSError(domain: "LivePhotoMetadata", code: 5, userInfo: [NSLocalizedDescriptionKey: "Cannot add metadata input"])
+        }
+        writer.add(metadataInput)
+
+        guard writer.startWriting() else {
+            throw writer.error ?? NSError(domain: "LivePhotoMetadata", code: 6)
+        }
+        guard reader.startReading() else {
+            throw reader.error ?? NSError(domain: "LivePhotoMetadata", code: 7)
+        }
+
+        writer.startSession(atSourceTime: .zero)
+
+        let stillImageTime = quickTimeMetadataItem(
+            key: "com.apple.quicktime.still-image-time",
+            value: NSNumber(value: Int8(-1)),
+            dataType: "com.apple.metadata.datatype.int8"
+        )
+        let stillGroup = AVTimedMetadataGroup(
+            items: [stillImageTime],
+            timeRange: CMTimeRange(start: .zero, duration: CMTime(value: 1, timescale: 600))
+        )
+        guard metadataAdaptor.append(stillGroup) else {
+            throw writer.error ?? NSError(domain: "LivePhotoMetadata", code: 8, userInfo: [NSLocalizedDescriptionKey: "Could not append still image time metadata"])
+        }
+        metadataInput.markAsFinished()
+
+        let queue = DispatchQueue(label: "livephoto.video.writer")
+        writerInput.requestMediaDataWhenReady(on: queue) {
+            while writerInput.isReadyForMoreMediaData {
+                if let sample = readerOutput.copyNextSampleBuffer() {
+                    if !writerInput.append(sample) {
+                        didFail = true
+                        reader.cancelReading()
+                        writerInput.markAsFinished()
+                        writer.cancelWriting()
+                        semaphore.signal()
+                        return
+                    }
+                } else {
+                    writerInput.markAsFinished()
+                    writer.finishWriting {
+                        semaphore.signal()
+                    }
+                    return
+                }
+            }
+        }
+    } catch {
+        didFail = true
+        fputs("Error: \(error.localizedDescription)\n", stderr)
+        semaphore.signal()
+    }
+}
+
+semaphore.wait()
+
+if didFail {
+    exit(1)
+}
+
+print("Wrote QuickTime Live Photo metadata: \(assetIdentifier)")