Create a temporary attachment for use as ad-hoc context on a Task Agent run. Submit as multipart/form-data. The type form field discriminates the payload carried on value: for FILE, send the file bytes as the value multipart part; for TEXT and URL, send the payload as the value form field. Reference the returned id in attachmentIds on a subsequent POST /v1/tasks/{id}/run call.

The returned attachment ID is currently only accepted by POST /v1/tasks/{id}/run (via the attachmentIds field). It is not supported by other endpoints.

Temporary attachments are intended for short-lived context (the same attachment can be referenced across retries of the same run) and should not be relied on for durable storage. Use the Knowledge API (POST /v1/knowledge) for content that should persist in your workspace.