持久图片附件
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附件 seam 将二进制图片的所有权与会话日志分离。生产方把经过校验的编码字节交给 ctx.attachments；只有对象完成持久化后，该服务才会发布不可变的内容寻址引用。会话事件和模型可见的 ImageBlock 包含该引用及其元数据，绝不包含浏览器对象 URL、宿主临时路径、提供方 URL 或 base64 数据。
未发送的浏览器草稿可以保留在内存中，原生客户端也可以将其暂存于操作系统临时存储。宿主接受用户消息后，会先把消息中的图片移到 <DSH_HOME>/attachments/v1 下，再追加用户事件。结构化模型图片输出遵循同样的先持久化、后追加事件规则。
来源：packages/attachment/attachment/src/types.ts
标识与经过校验的元数据
AttachmentId 是带类型标记的不透明字符串。本地后端目前生成 sha256:<digest>，但消费方既不能解析这种表示，也不能据此派生文件系统路径。
/** Raster image formats accepted by the version-one attachment path. */
type ImageMediaType = 'image/png' | 'image/jpeg' | 'image/webp' | 'image/gif'/** Durable, serializable reference to one immutable normalized image. */
interface ImageAttachmentRef {
/** Opaque storage identifier; never a filesystem path or bearer URL. */
attachmentId: AttachmentId
/** Media type verified from the stored bytes. */
mediaType: ImageMediaType
/** Exact encoded byte length. */
bytes: number
/** Intrinsic encoded width in pixels. */
width: number
/** Intrinsic encoded height in pixels. */
height: number
/** Optional display name stripped of local path information. */
name?: string
/**
* Input dimensions after applying EXIF orientation and before normalization
* scaling. Present only when normalization reduced the image.
*/
originalDimensions?: {
width: number
height: number
}
}/** Deployment-resolved limits used by upload admission and request buffering. */
interface ImageAttachmentLimits {
maxImageBytes: number
maxImagesPerMessage: number
maxMessageImageBytes: number
maxImagePixels: number
/** Maximum intrinsic width and maximum intrinsic height in pixels for one image. */
maxImageDimension: number
mediaTypes: readonly ImageMediaType[]
}本地后端每条消息最多准入 20 张图片，源图编码数据总量不超过 200 MiB。单张源图不得超过 20 MiB、64,000,000 像素和单边 8192 像素。这些源文件限制先于独立的规范化阶段执行；该阶段默认把长边限制为 2048 像素，把编码数据限制为 4 MiB。
引用记录固有尺寸和编码长度，使客户端无需先解码即可排布历史记录；每次权威读取仍会根据对象重新校验摘要、媒体签名、尺寸和元数据。
提交与经校验读取的数据
/** Base64-encoded image upload accompanying one wire request. */
interface EncodedImageAttachment {
/** Declared media type, verified against the decoded bytes during admission. */
mediaType: ImageMediaType
/** Canonical base64 encoding of the image bytes. */
data: string
/** Optional display name; it is never interpreted as a path. */
name?: string
}/** Request to validate and durably commit one image. */
interface SaveImageAttachment {
data: Uint8Array
/** Caller-declared media type, checked against fully decoded bytes. */
mediaType: ImageMediaType
/** Optional browser/provider display name; it is never interpreted as a path. */
name?: string
}/** Stored image bytes returned after reference and digest verification. */
interface StoredImageAttachment {
ref: ImageAttachmentRef
data: Uint8Array
}/** Deterministic request-image policy selected by one exact model route. */
interface ImageRequestPolicy {
/** Maximum width multiplied by height after aspect-preserving projection. */
maxPixels: number
/** Encoded-byte cap before base64 expansion or Files API upload. */
maxBytes: number
}/** Cached request version derived from one provider-independent normalized attachment. */
interface RequestImageAttachment {
/** Cache and upload-index key over the attachment id, policy, and fixed encoder parameters. */
variantId: ImageVariantId
/** Durable normalized attachment from which this request version was derived. */
attachment: ImageAttachmentRef
/** Encoded request bytes. */
data: Uint8Array
mediaType: ImageMediaType
bytes: number
width: number
height: number
/** Provider-compatible sample depth proven after request encoding. */
depth: 'uchar'
/** Provider-compatible color space proven after request encoding. */
space: 'srgb'
/** Whether the encoded request version retains an alpha channel. */
hasAlpha: boolean
}saveImage() 准备并原子提交提供方无关的规范化附件，然后直接返回 ImageAttachmentRef。saveImages() 在发布批次前为每个成员各准备一次经过验证的附件，因此校验拒绝不会留下部分对象，发布也不会重复解码或选择质量。admitEncodedImages() 是面向 base64 上传的 wire 入口，把张数、聚合字节和有序批量准入交给 saveImages()。readImage() 校验来自已授权会话路径的规范化附件。readImageRequest() 按确切路由的像素和字节预算派生并缓存请求版本；新条目在发布前完整解码，缓存命中只做有界元数据探测。调用方需要有序批次时，对单数方法使用 Promise.all。本地实现按需编码首选候选、合并相同请求身份的并发任务、允许每个等待方单独取消、没有等待方时停止共享任务，并通过实例级限流器限制全部变换，默认同时执行两项。该服务不规定保留策略：恢复和 fork 后的会话可能共享对象，因此基于引用的垃圾回收会延期实现，不与单个会话的删除绑定。
Cordis API
Generated from source by scripts/gen-cordis-catalog.ts (verified fresh by pnpm run verify-cordis-catalog in doc-sync; regenerate with pnpm run gen-cordis-catalog) — the language sides differ only in locale-specific paired document paths. Signature blocks use a ts cordis-catalog fence and keep the original source JSDoc; dispatch modes are defined in the primer, and the framework-inherited ctx API lives in cordis-api/inherited.md.
ctx.attachments — AttachmentStore (abstract seam)
Immutable binary attachment service. Implementations validate bytes before publishing a reference.
/**
* Validate one image without persisting it.
* Batch callers validate every member before saving any member.
* @param input - encoded bytes, declared media type, and optional display name.
* @returns completion after the encoded raster has been fully decoded.
*/
abstract validateImage(input: SaveImageAttachment): Promise<void>
/**
* Validate and durably commit one ordered image batch.
* @param inputs - encoded images in owning-message order.
* @returns durable normalized attachment references in the same order after every member succeeds.
*/
async saveImages(inputs: readonly SaveImageAttachment[]): Promise<readonly ImageAttachmentRef[]>
/**
* Validate and durably commit one image before its owning session event is appended.
* The returned reference describes the persisted normalized image. When
* normalization reduces the raster, its `originalDimensions` records the
* orientation-applied input dimensions.
* @param input - encoded bytes, declared media type, and optional display name.
* @returns the durable content-addressed normalized image reference.
*/
abstract saveImage(input: SaveImageAttachment): Promise<ImageAttachmentRef>
/**
* Read one image and verify that bytes still match the recorded reference.
* @param ref - durable reference from the session log.
* @param signal - optional cancellation for backend read and verification work.
* @returns the verified bytes and normalized attachment reference.
* @throws the signal reason when aborted, or a storage error when verification fails.
*/
abstract readImage(ref: ImageAttachmentRef, signal?: AbortSignal): Promise<StoredImageAttachment>
/**
* Generate or read one deterministic model-request version from the stored normalized image.
* @param ref - durable provider-independent normalized attachment reference.
* @param policy - exact route pixel and encoded-byte budget.
* @param signal - optional cancellation.
* @returns request bytes and the cache/upload identity covering every transform input.
*/
readImageRequest( ref: ImageAttachmentRef, policy: ImageRequestPolicy, signal?: AbortSignal, ): Promise<RequestImageAttachment>