Chart session checkpoints as their own cache bucket

src/app/view/stats.rs

@@ -371,21 +371,25 @@ impl App {
         .into()
     }
 
-    /// Disc usage of both cache buckets, split by age. The bar is the age
-    /// distribution of what is stored; the budget governs the transient store
-    /// only and is reported on its own row.
+    /// Disc usage of both cache buckets. The bar splits the transient store by
+    /// age — the order the budget evicts in — and carries the session
+    /// checkpoints as one further segment, since those are only freed with
+    /// their session and so compete for disc without ever ageing out.
     fn cache_explorer(&self) -> Element<'_, Message> {
         let usage = &self.kv_cache_report;
         let total = usage.total_bytes();
         let capacity = total.max(1);
+        let segments = crate::metrics::CACHE_AGE_BUCKETS
+            .iter()
+            .enumerate()
+            .map(|(index, (label, _))| (*label, usage.age_bytes[index], AGE_COLORS[index]))
+            .chain([("Sessions", usage.session_bytes, SESSION_COLOR)]);
         let mut bar = row![].height(14).spacing(2);
         let mut legend = column![].spacing(6);
-        for (index, (label, _)) in crate::metrics::CACHE_AGE_BUCKETS.iter().enumerate() {
-            let bytes = usage.age_bytes[index];
+        for (label, bytes, color) in segments {
             if bytes == 0 {
                 continue;
             }
-            let color = AGE_COLORS[index];
             bar = bar.push(
                 container(Space::new(Length::Fill, Length::Fill))
                     .width(Length::FillPortion(portion(bytes, capacity)))
@@ -394,7 +398,7 @@ impl App {
             legend = legend.push(
                 row![
                     container(Space::new(9, 9)).style(move |_| chart_bar_style(color)),
-                    text(*label).size(12).color(muted_text()),
+                    text(label).size(12).color(muted_text()),
                     Space::with_width(Length::Fill),
                     text(format!(
                         "{} · {:.0}%",
@@ -497,6 +501,9 @@ impl App {
     }
 }
 
+/// Sessions sit outside the age scale: they are not evicted, only deleted.
+const SESSION_COLOR: Color = Color::from_rgb(0.85, 0.44, 0.56);
+
 /// Age buckets from green (fresh) to grey (past every hit half-life).
 const AGE_COLORS: [Color; 5] = [
     Color::from_rgb(0.28, 0.69, 0.44),