Sidebar cost total now uses displayed_session_cost_for_currency so the
high-water mark protects against cost reversal during API reconciliation
(#244). The session+agents breakdown is only shown when it matches the
displayed total; otherwise a single total line is rendered.
Add SessionMetadata::copy_cost_from to eliminate the last remaining
manual four-field cost copy (fork-session path).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
lbcheng
b6b1599b8c