Adds the presigned-upload plumbing Outline's own web client uses for
any file upload, not just avatars: attachments.create requests an
upload target (server-assigned key, ACL, a short-lived signed form),
then a direct multipart POST to that target (uploadUrl/form) actually
uploads the bytes — confirmed against a live server's own request/
response shapes pulled from network capture. MultipartFormDataBuilder
is a pure, fully-tested function (no network) building that S3-style
presigned-POST body.
uploadAttachmentFile deliberately sends no Bearer/CSRF header — the
presigned form's `sig` field is what authorizes that specific request,
same as an S3 presigned POST; flagged as best-effort pending live
confirmation, cheap to add if the server turns out to also want one.
UpdateUserAvatarRequest (users.update, avatar only) needed a custom
encode(to:) — Swift's synthesized Encodable omits nil Optional keys
via encodeIfPresent, but removing an avatar needs a literal
"avatarUrl": null in the body, not the key missing. Confirmed the
request shape (id + avatarUrl) from the captured request's
Content-Length matching that shape and no shorter alternative.
6 new tests (multipart body structure/field ordering, explicit-null
encoding, create/upload/update round trip) — 63/63 passing.
Puranjay Savar Mattas
373c681c10