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Assemble the structure of a forwarded message: prefix detection · case 05

An existing "FWD:" prefix is not recognised, so forwarded subjects accumulate prefixes.

Member previewVariant 5 · 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
upper-case existing prefix	`{"structure": "text", "subject": "Fwd: FWD: plan 5"}`	`{"structure": "text", "subject": "FWD: plan 5"}`	Failed

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