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
+    /// Disc usage of both cache buckets. The bar splits the transient store by
-    /// distribution of what is stored; the budget governs the transient store
+    /// age — the order the budget evicts in — and carries the session
-    /// only and is reported on its own row.
+    /// 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() {
+        for (label, bytes, color) in segments {
-            let bytes = usage.age_bytes[index];
             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),

src/metrics.rs

@@ -707,7 +707,8 @@ pub(crate) struct KvCacheReport {
     pub(crate) session_files: u64,
     pub(crate) transient_bytes: u64,
     pub(crate) transient_files: u64,
-    /// Bytes per [`CACHE_AGE_BUCKETS`] entry, both buckets combined.
+    /// Bytes per [`CACHE_AGE_BUCKETS`] entry, transient store only: session
+    /// checkpoints never age out, so their age says nothing about eviction.
     pub(crate) age_bytes: [u64; CACHE_AGE_BUCKETS.len()],
     pub(crate) entries: Vec<KvCacheEntry>,
 }
@@ -752,11 +753,13 @@ pub(crate) fn kv_cache_report(root: &Path, budget_bytes: u64) -> KvCacheReport {
                 .ok()
                 .and_then(|modified| now.duration_since(modified).ok())
                 .map_or(0, |age| age.as_secs());
+            if transient {
                 let bucket = CACHE_AGE_BUCKETS
                     .iter()
                     .position(|(_, limit)| age_seconds < *limit)
                     .unwrap_or(CACHE_AGE_BUCKETS.len() - 1);
                 report.age_bytes[bucket] += bytes;
+            }
             // Index files are counted in the totals but folded into their
             // checkpoint's row.
             if path.extension().is_some_and(|value| value == "meta") {
@@ -915,8 +918,9 @@ mod tests {
         assert_eq!(report.session_files, 1);
         assert_eq!(report.transient_bytes, 140);
         assert_eq!(report.transient_files, 2);
-        // Fresh files in the first bucket, the two-day-old one in "1–7d".
+        // Only the transient store is bucketed by age: its fresh index file in
-        assert_eq!(report.age_bytes[0], 340);
+        // the first bucket, its two-day-old checkpoint in "1–7d".
+        assert_eq!(report.age_bytes[0], 40);
         assert_eq!(report.age_bytes[3], 100);
         assert_eq!(
             (