The titler receives the opening message AFTER @-reference expansion, so
the Desktop's generated pasted_content @file: ref arrives with a
'--- Context Warnings ---' (or '--- Attached Context ---') footer. That
footer made the ref-only check in build_title_input fail, so the live
wire capture showed the path + warning leading the title-model input
with 'Pasted content: ...' appended after it. Strip the expander footer
when a preview is present, so a paste-only opener lets the preview lead.
Invariant: test_expanded_paste_ref_footer_does_not_demote_the_preview
(red on a5dac801, green here). Re-checked on the wire against the stub
model: title input now starts with the pasted topic, no @file:/warning.
85f5f560c3