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Assemble the structure of a forwarded message: related without images · case 04

An HTML forward without inline images gets an empty multipart/related wrapper.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

original {subject, body_type ("text" or "alternative"), attachments [names], inline [image names]}. Subjects get a "Fwd: " prefix unless they already start with "fwd:" (case-insensitive). mode "attach" produces mixed(text,message/rfc822): the original travels whole, attachments included. mode "inline" copies the body: alternative(text,html), with related(html, images...) when the original has inline images (kept only when html exists), or text; original attachments follow in their original order inside mixed(...).

Why this case matters

Forwarding rebuilds a MIME tree; errors duplicate attachments, lose inline images or stack Fwd: prefixes.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
attachment order	`{"structure": "mixed(alternative(text,related(html,)),b.pdf,a.doc,c4.txt)", "subject": "Fwd: s"}`	`{"structure": "mixed(alternative(text,html),b.pdf,a.doc,c4.txt)", "subject": "Fwd: s"}`	Failed

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