#141 feat(inboxes): accept path attachments on drafts

POST /inboxes/{inbox_id}/drafts and PATCH /inboxes/{inbox_id}/drafts/{draft_id} now accept path attachments, like POST /emails. They used to return a 422. API change: resend/resend-monorepo#13475 (live in prod).

Changes

InboxDraftAttachmentInput:

• Only filename is required now. content is required without path, and path is required without content.
• New path property.
• content_type is required with content. With path, it defaults to the downloaded file's content type.

The create/update attachments descriptions and the create-draft operation description now say that a path file is downloaded when the request is made (not when the draft is sent). They also give the 422 cases:

• a path that doesn't start with http/https, or can't be downloaded
• downloads that take more than 20 seconds together
• a total over 25 MB, downloaded files included

Verification

• yq eval . resend.yaml parses. redocly lint gives 184 warnings and 0 errors, the same as main.
• Each rule checked live against api.resend.com:
  • path + filename → 201, and the content type comes from the download
  • path without filename → 422
  • content without content_type → 422
  • ftp:// path → 422
  • PATCH with path → 200
  • content + path → content wins

Linear: DEV-2418