Attachments

Upload a file to the session, then attach the returned reference to a message.

const ref = await client.blobs.upload({
  sessionId,                       // required: a blob is scoped to one session
  data: base64,                    // no data-URL prefix; 8 MiB cap on the decoded bytes
  contentType: "application/pdf",
  name: "report.pdf"              // optional label
})

await client.sessions.send({
  id: sessionId,
  message: "Compare this report with the launch-plan source. What changed?",
  attachments: [ref]
})

The ref is content-addressed, so uploading identical bytes twice is one blob.

Images and text-shaped documents (PDF, plain text, CSV, JSON, Markdown) are accepted. An image or a PDF is rendered to the model as a native file part; a text document is rendered inline.

Unsupported content types are rejected at upload. If an attached reference cannot be read during a turn, a visible marker records the failure. Model support for file types still depends on the provider and model you select.

Sending a message exactly once, with the idempotencyKey on sessions.send, is on enqueue and steer. The create-side key is on sessions.