Attachments

You move bytes between three places:

• Gini upload space — <id> references for files the user attached in chat, downloaded from a URL, or promoted from workspace.
• External URLs — any https endpoint (signed PUT/GET URLs from APIs, raw file URLs, etc.).
• Workspace files — files on disk under the agent's workspace root.

This skill ships four scripts you invoke via skill_run, plus a recipe for each common direction. The base primitive vision_query (asking the model to describe an image upload) is in core, not here — combine it with the scripts below when the model needs to "see" what it just moved.

When to use this skill

• The user attached an image and asks you to file a Linear / GitHub / Notion issue with it.
• The user pasted a URL pointing to file content (Linear attachment, GitHub raw, generic https URL) and asks you to ingest or describe it.
• code_exec / terminal_exec produced a workspace file (chart, exported PDF, downloaded artifact) and you need to send it somewhere or run vision_query on it.
• An MCP server returned an assetUrl / signed URL pointing to file content and you want to do something with the bytes.

The four scripts

signed-upload — chat-attached upload → external URL

PUT bytes from a Gini upload (chat attachment, downloaded file, promoted workspace file) to a signed URL the model obtained from an API's prepare step. Used in 3-step attachment flows: prepare via the API → signed-upload → finalize via the API.

skill_run({
  skill: "attachments",
  script: "signed-upload",
  args: {
    uploadId: "abc-123-...",        // from the user message marker, signed-download, or promote-file
    url: "https://uploads.linear.app/...?X-Goog-...",
    headers: {                       // pass through whatever the prepare step returned, verbatim
      "content-type": "image/png",
      "x-goog-content-length-range": "36116,36116"
    }
  }
})
// → { ok: true, status: 200, bytesSent: 36116 }
//   or { ok: false, status, error: "..." }

Only https URLs are accepted. The script never fabricates headers — pass through what the prepare step gave you. Signed URLs typically expire in 60 seconds; move immediately from prepare → PUT.

signed-download — external URL → Gini upload

GET bytes from a URL and store them as a Gini upload. Used to ingest content (Linear attachment URLs, GitHub raw files, user-pasted URLs, S3 presigned downloads) into the upload-addressable space so vision_query or signed-upload can consume them.

skill_run({
  skill: "attachments",
  script: "signed-download",
  args: {
    url: "https://uploads.linear.app/asset/abc.png",
    headers: { authorization: "Bearer ..." },  // optional, depends on the URL
    filename: "screenshot.png"                  // optional, defaults to URL basename
  }
})
// → { ok: true, uploadId: "xyz-456-...", mimeType: "image/png", size: 36116 }

Only https URLs accepted. Body capped at 50MB. Inferred mime comes from the content-type response header; falls back to application/octet-stream.

promote-file — workspace file → Gini upload

Register a workspace-relative file as a Gini upload. Used when code_exec / terminal_exec left a file on disk that you want to attach somewhere or run vision_query on.

skill_run({
  skill: "attachments",
  script: "promote-file",
  args: {
    path: ".charts/sales-q4.png",
    mimeType: "image/png"  // optional, sniffed from extension when omitted
  }
})
// → { ok: true, uploadId: "ghi-789-...", mimeType: "image/png", size: 24512 }

Path is workspace-relative and escape-protected (same guard as file_read).

When the user asked you to send / show them a file (a screenshot, a chart, a generated picture, a PDF, a CSV), promote-file is all you need. Its result includes an attachmentMarkdown field — a ready-to-paste markdown tag like ![image](gini-upload://<id>) (for images) or [name](gini-upload://<id>) (for other files). Paste that tag verbatim into your reply at the spot where the attachment should appear — it renders inline there (an image shows as a picture, any other file as a download chip), so you can place a screenshot mid-sentence, right where you're describing it. Do not paste the raw uploadId on its own — use the provided attachmentMarkdown tag. The bare uploadId is only an argument to a follow-up tool (signed-upload, vision_query, materialize), never user-facing text.

materialize — Gini upload → workspace file

The inverse of promote-file: write a Gini upload's bytes to a workspace file. Used when you need a chat-attached (or downloaded / promoted) upload on disk so terminal_exec, code_exec, or a git flow can read the actual file — e.g. committing an image to an asset branch.

skill_run({
  skill: "attachments",
  script: "materialize",
  args: {
    uploadId: "abc-123-...",   // from the user message marker, signed-download, or promote-file
    path: "assets/diagram.png" // optional, workspace-relative; defaults to the manifest filename
  }
})
// → { ok: true, path: "assets/diagram.png", absPath: "/abs/.../assets/diagram.png",
//     mimeType: "image/png", size: 36116, filename: "diagram.png" }

Destination is workspace-relative and escape-protected (same guard as promote-file). When path is omitted it defaults to the upload's original filename (basename, sanitized) at the workspace root, or <uploadId>.<ext> when the manifest has none. absPath is the absolute on-disk path — hand it to commands that need an absolute path (e.g. git hash-object -w <absPath>).

Recipe patterns

Filing an issue with a chat-attached screenshot (providers with a signed-upload API)

Applies to providers that expose a public prepare → PUT → finalize upload API (Linear, S3 / any presigned-URL backend):

1. Prepare — call the provider's prepare-upload tool via mcp_call. Linear: prepare_attachment_upload({issue, filename, contentType, size}). The response carries the signed URL, headers to send verbatim, and an asset URL for the finalize step.
2. PUT bytes — skill_run({skill: "attachments", script: "signed-upload", args: {uploadId, url: <prepared.url>, headers: <prepared.headers>}}).
3. Finalize — call the provider's finalize tool. Linear: create_attachment_from_upload({issue, assetUrl, title}).

uploadId is in the user message marker: Attached image uploads (in order): - <id> (<mime>, <bytes> bytes). Read the mime and size from the same marker so the prepare call doesn't fail with EntityTooLarge / EntityTooSmall.

Targets without a public upload API (e.g. GitHub issues) don't use this recipe — materialize the upload to disk instead (recipe below) and follow that integration skill's own attach flow.

Reading a screenshot the user posted as a URL

1. skill_run({skill: "attachments", script: "signed-download", args: {url}}) → {uploadId}.
2. vision_query({uploadId, question: "describe this image"}) → {answer}.

Describing an existing attachment on a Linear issue

1. mcp_call({server: "linear", tool: "get_attachment", arguments: {id: "..."}}) → response includes the asset URL.
2. skill_run({skill: "attachments", script: "signed-download", args: {url: <assetUrl>}}) → {uploadId}.
3. vision_query({uploadId, question: "..."}) → {answer}.

Sending a generated chart to Linear

1. Generate via code_exec (matplotlib / d3 / etc.), save under ./chart.png.
2. skill_run({skill: "attachments", script: "promote-file", args: {path: "chart.png"}}) → {uploadId, mimeType, size}.
3. Run the 3-step Linear flow with that uploadId.

Putting a chat-attached screenshot on disk

When an integration needs the actual file (not an upload id) — e.g. a git flow that has to git hash-object the bytes:

1. skill_run({skill: "attachments", script: "materialize", args: {uploadId: "<id-from-marker>"}}) → {path, absPath}.
2. Hand off absPath to the integration skill that consumes a file — it owns the provider-specific attach flow (e.g. github-issues' "Attaching an image to an issue").

Chat-attached files are already delivered for you

When the user attaches a file in chat, the runtime delivers it to you in core — you do not need this skill to read it. The content arrives in the user message (a native document part, or inlined extracted text wrapped in <<<BEGIN/END UNTRUSTED FILE <nonce>>>> markers), and the file is already saved to your workspace at the uploads/<id>/<name> path named in the message. Read the workspace file directly with file_read / code_exec when you need more than the inlined preview. See ADR chat-file-attachments.md. This skill is for agent-initiated byte movement (URL downloads, promoting generated files, sending to an external system), not for reading the user's chat uploads.

Rules

1. Always invoke through skill_run with skill: "attachments". The scripts read JSON from stdin and write JSON to stdout — don't try to terminal_exec them by hand.
2. Pass signed-upload headers through verbatim from the prepare step's response. Omitting one or rewriting the casing usually means a 403 from the storage backend.
3. Signed URLs expire fast (often 60 seconds). On signed-upload failure, re-run the provider's prepare step rather than retrying with the stale URL.
4. Don't attempt vision on non-image uploads. vision_query only accepts image/png and image/jpeg. Convert via terminal_exec (sips -s format jpeg ...) and promote-file the result if you need to vision a different format.
5. The provider-specific prepare/finalize (or other attach) steps live in each integration's skill (Linear's SKILL.md documents Linear's args; github-issues documents GitHub's attach flow). This skill owns the byte-PUT / byte-GET / materialize middle steps only.