Move token/cache/cost metrics from the expandable per-block usage button
into a persistent status bar rendered in the agent input area. This gives
always-visible feedback without requiring user interaction.
- Add render_session_status_bar to agent input showing context %, cache
hit rate, and cost
- Persist cache/cost totals in ConversationUsageMetadata for session restore
- Remove render_usage_button, ToggleIsUsageFooterExpanded action, and
UsageFooterToggled event
- Remove "Request tokens: --" debug block footer overlay
- Fix has_footer() to return false so blocks no longer reserve phantom
footer space (root cause of padding/margin issue)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
