fix(tui): show real-time cost total in sidebar and /cost commands

Sidebar cost line used displayed_cost_high_water for the total but
real values for the session/agent breakdown, so total did not equal
session + agents. Use real-time sums everywhere for internal
consistency.

/cost and /tokens commands now include sub-agent costs in the
displayed total, matching the footer chip.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

crates/tui/src/commands/debug.rs

@@ -73,7 +73,10 @@ pub fn tokens(app: &mut App) -> CommandResult {
         .replace("{total}", &app.session.total_tokens.to_string())
         .replace(
             "{cost}",
-            &app.format_cost_amount_precise(app.session_cost_for_currency(app.cost_currency)),
+            &app.format_cost_amount_precise(
+                app.session_cost_for_currency(app.cost_currency)
+                    + app.subagent_cost_for_currency(app.cost_currency),
+            ),
         )
         .replace("{api_messages}", &message_count.to_string())
         .replace("{chat_messages}", &chat_count.to_string())
@@ -83,9 +86,11 @@ pub fn tokens(app: &mut App) -> CommandResult {
 
 /// Show session cost breakdown
 pub fn cost(app: &mut App) -> CommandResult {
+    let total = app.session_cost_for_currency(app.cost_currency)
+        + app.subagent_cost_for_currency(app.cost_currency);
     let report = tr(app.ui_locale, MessageId::CmdCostReport).replace(
         "{cost}",
-        &app.format_cost_amount_precise(app.session_cost_for_currency(app.cost_currency)),
+        &app.format_cost_amount_precise(total),
     );
     CommandResult::message(report)
 }

crates/tui/src/tui/sidebar.rs

@@ -671,9 +671,9 @@ fn render_context_panel(f: &mut Frame, area: Rect, app: &App) {
     )));
 
     // ── Session cost ─────────────────────────────────────────────
-    let total_cost = app.displayed_session_cost_for_currency(app.cost_currency);
     let session_cost = app.session_cost_for_currency(app.cost_currency);
     let agent_cost = app.subagent_cost_for_currency(app.cost_currency);
+    let total_cost = session_cost + agent_cost;
     lines.push(Line::from(Span::styled(
         format!(
             "cost: {} (session {} + agents {})",