Create Email Attachment Target

Ask for a presigned target to upload a one-off email attachment.

Where to PUT the bytes, and the token that names them to a workflow.

token is what the app passes as an attachment-typed app_invocation input — the only part of an attachment that may travel in a run payload. That input takes one token or a list of them, so several files mean several of these targets, one per file. filename is the sanitized name the recipient will actually see, which may differ from the one requested.

max_bytes and max_files are the per-EMAIL budget, not a per-file one: they are reported so an app can reject an over-budget selection while the person is still looking at the picker, instead of failing the workflow after the run has started.