71 lines
3.3 KiB
Markdown
71 lines
3.3 KiB
Markdown
# 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`](../cordis-catalog/services.md#ctxattachments); the service publishes an immutable content-addressed reference only after the object is durable. Session events and model-visible `ImageBlock`s contain that reference and metadata, never a browser object URL, host temporary path, provider URL, or base64 payload.
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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.
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Source: [`packages/attachment/attachment/src/types.ts`](../../packages/attachment/attachment/src/types.ts)
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## Identity and verified metadata
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`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.
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```ts type-equiv
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/** Raster image formats accepted by the version-one attachment path. */
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type ImageMediaType = 'image/png' | 'image/jpeg' | 'image/webp' | 'image/gif'
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```
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```ts type-equiv
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/** Durable, serializable metadata for one immutable image object. */
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interface ImageAttachmentRef {
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/** Opaque storage identifier; never a filesystem path or bearer URL. */
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attachmentId: AttachmentId
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/** Media type verified from the stored bytes. */
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mediaType: ImageMediaType
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/** Exact encoded byte length. */
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bytes: number
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/** Intrinsic encoded width in pixels. */
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width: number
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/** Intrinsic encoded height in pixels. */
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height: number
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/** Optional display name stripped of local path information. */
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name?: string
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}
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```
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```ts type-equiv
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/** Deployment-resolved limits shared by upload consumers and UI preflight. */
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interface ImageAttachmentLimits {
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maxImageBytes: number
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maxImagesPerMessage: number
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maxMessageImageBytes: number
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maxImagePixels: number
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mediaTypes: readonly ImageMediaType[]
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}
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```
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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.
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## Commit and verified-read payloads
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```ts type-equiv
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/** Request to validate and durably commit one image. */
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interface SaveImageAttachment {
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data: Uint8Array
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/** Caller-declared media type, checked against magic bytes. */
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mediaType: ImageMediaType
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/** Optional browser/provider display name; it is never interpreted as a path. */
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name?: string
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}
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```
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```ts type-equiv
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/** Stored image bytes returned after reference and digest verification. */
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interface StoredImageAttachment {
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ref: ImageAttachmentRef
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data: Uint8Array
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}
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```
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`saveImage()` validates bytes and atomically commits one object before returning its reference. `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.
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