deepseek-harness/docs/subsystems/attachment.md

Durable Image Attachments

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The attachment seam separates binary image ownership from the session log. A producer gives validated encoded bytes to ctx.attachments; the service publishes an immutable content-addressed reference only after the object is durable. Session events and model-visible ImageBlocks contain that reference and metadata, never a browser object URL, host temporary path, provider URL, or base64 payload.

Unsent browser drafts may stay in memory and native clients may stage them in operating-system temporary storage. Once the host accepts a user message, its images move below <DSH_HOME>/attachments/v1 before the user event is appended. Structured model image output follows the same persist-before-event rule.

Source: packages/attachment/attachment/src/types.ts

Identity and verified metadata

AttachmentId is a branded opaque string. The local backend currently emits sha256:<digest>, but consumers must neither parse that representation nor derive a filesystem path from it.

/** Raster image formats accepted by the version-one attachment path. */
type ImageMediaType = 'image/png' | 'image/jpeg' | 'image/webp' | 'image/gif'

/** Durable, serializable metadata for one immutable image object. */
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
}

/** Deployment-resolved limits used by upload admission and request buffering. */
interface ImageAttachmentLimits {
  maxImageBytes: number
  maxImagesPerMessage: number
  maxMessageImageBytes: number
  maxImagePixels: number
  mediaTypes: readonly ImageMediaType[]
}

The reference records intrinsic dimensions and encoded length so clients can lay out history without decoding first, while every authoritative read still re-checks digest, media signature, dimensions, and metadata against the object.

Commit and verified-read payloads

/** 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
}

saveImage() validates bytes and atomically commits one object before returning its reference. validateImage() runs the same admission checks without persisting anything; batch callers validate every member through it before saving any member, so validation rejection leaves no partial objects behind. readImage() accepts a reference from an authorized session path and returns bytes only after integrity verification. The service is deliberately retention-neutral: resumed and forked sessions may share objects, so reference-aware garbage collection is deferred rather than tied to any one session's deletion.

Cordis surface

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) — this section is byte-identical in both language sides of the page. 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 surface 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 image before its owning session event is appended.
 * @param input - encoded bytes, declared media type, and optional display name.
 * @returns a durable content-addressed 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.
 * @returns the verified bytes and canonical reference.
 */
abstract readImage(ref: ImageAttachmentRef): Promise<StoredImageAttachment>

Source: packages/attachment/attachment/src/index.ts:29