diff --git a/ui/src/views/Forecast.jsx b/ui/src/views/Forecast.jsx
index 8afcbae..d3e298f 100644
--- a/ui/src/views/Forecast.jsx
+++ b/ui/src/views/Forecast.jsx
@@ -203,15 +203,21 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   // fresh view has no depth set, so the whole tree appears expanded. Re-apply the
   // depth we last set once the redraw has settled.
   // ---------------------------------------------------------------- DEBUG
-  // Temporary instrumentation for the "row groups re-expand on refocus" bug.
-  // set_depth() and per-node expand/collapse live on the *view*, not in
-  // ViewConfig, so a rebuilt view loses both. These lines exist to show whether
-  // that is what happens. Remove once the cause is known.
+  // Tracing for the "row groups re-expand on refocus" bug. set_depth() and
+  // per-node expand/collapse live on the *view*, not in ViewConfig, so every
+  // view rebuild starts fully expanded and we have to re-apply depth ourselves.
+  // Silent unless localStorage.pf_debug is set, since this is the kind of thing
+  // you want back the next time the timing shifts.
+  //
+  //   localStorage.setItem('pf_debug', '1')   // then reload
   const viewSeqRef = useRef(0)
   const viewIdsRef = useRef(new WeakMap())
   const lastViewIdRef = useRef(null)
 
   function dbg(msg, extra) {
+    let on = false
+    try { on = !!localStorage.getItem('pf_debug') } catch { /* private mode */ }
+    if (!on) return
     const t = new Date().toISOString().slice(11, 23)
     if (extra !== undefined) console.log(`[pf-depth ${t}] ${msg}`, extra)
     else                     console.log(`[pf-depth ${t}] ${msg}`)
@@ -226,6 +232,9 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   // Read the viewer's current view and report whether it is the same object we
   // saw last time. A changed id means the view was discarded and rebuilt.
   async function probeView(where) {
+    let on = false
+    try { on = !!localStorage.getItem('pf_debug') } catch { /* private mode */ }
+    if (!on) return
     const viewer = viewerRef.current
     if (!viewer) return dbg(`probe(${where}): no viewer`)
     try {