Restore row depth only after the viewer has actually gone away

Driving the re-apply from the observer callbacks caught the refocus case but
fired on far more than that: ResizeObserver reports every reflow, so
dragging the panel, a scrollbar appearing, or anything that changed the
layout re-applied the stored depth and discarded whatever had just been
expanded by hand. From the outside that is the pivot snapping to a different
layout while clicking around.

Going away is what discards the view; a reflow is not. So the callbacks now
record the departure -- lost intersection, collapsed to zero size, or a
hidden document -- and only a return after one of those restores anything.
The flag clears once the depth is back, so one departure causes one restore.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/src/views/Forecast.jsx

@@ -226,6 +226,9 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   const viewSeqRef = useRef(0)
   const viewIdsRef = useRef(new WeakMap())
   const lastViewIdRef = useRef(null)
+  // set when the viewer stops being visible; only then is there anything to
+  // restore, and only then may a callback re-apply depth
+  const wentAwayRef   = useRef(false)
 
   function dbg(msg, extra) {
     let on = false
@@ -301,6 +304,12 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
       if (!viewerRef.current)                      return dbg('bail: no viewer')
       if (expandDepthRef.current == null)          return dbg('bail: no depth recorded (toolbar EXPAND never used, or per-node +/- only)')
       if (queued)                                  return dbg('bail: already queued')
+      // Only after the viewer has actually been away. Re-applying on every
+      // callback meant a panel drag, an appearing scrollbar or any reflow reset
+      // the tree to the stored depth, discarding whatever had just been expanded
+      // by hand -- the pivot "snapping to a different layout" while clicking
+      // around. Going away is what discards the view; a reflow does not.
+      if (!wentAwayRef.current)                    return dbg('bail: viewer never went away, nothing to restore')
       queued = true
       // Let the viewer finish its own redraw first, then wait for it to actually
       // have a table again. A fixed delay loses this race most of the time -- the
@@ -312,7 +321,10 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
         try {
           const d = expandDepthRef.current
           if (d == null) return dbg('re-apply aborted: depth became null')
-          if (await applyDepthWhenReady(d)) dbg(`re-apply done depth=${d}`)
+          if (await applyDepthWhenReady(d)) {
+            wentAwayRef.current = false
+            dbg(`re-apply done depth=${d}`)
+          }
         } catch (err) {
           dbg('re-apply THREW', err)
         } finally {
@@ -334,26 +346,41 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
     let settle = null
     const onObserved = (ev) => {
       const d = ev.detail || {}
-      // A resize to zero, or losing intersection, is the element going away --
+      // Losing intersection, or collapsing to zero size, is the element going
-      // nothing to re-apply to yet. Only act on it coming back.
+      // away: record it, because that is when the view gets discarded.
-      const returning = d.entries?.some(e =>
+      const leaving = d.entries?.some(e =>
-        e.isIntersecting === true || (e.width > 0 && e.height > 0))
+        e.isIntersecting === false || (e.width === 0 && e.height === 0))
-      if (!returning) return
+      if (leaving) { wentAwayRef.current = true; return dbg(`observer ${d.kind} -> viewer went away`) }
+
+      // A resize with a non-zero size is an ordinary reflow. It is not a
+      // restoration, so it must not re-apply anything.
+      if (!wentAwayRef.current) return
+
       clearTimeout(settle)
       settle = setTimeout(() => {
-        dbg(`observer ${d.kind} settled -> viewer visible again`)
+        dbg(`observer ${d.kind} settled -> viewer back after going away`)
         reapply({ type: `observer:${d.kind}` })
       }, 150)
     }
 
+    // A hidden tab is the other way the viewer goes away, and the one the
+    // observers may not report on every browser.
+    const onVisibility = (ev) => {
+      if (document.visibilityState !== 'visible') {
+        wentAwayRef.current = true
+        return dbg('document hidden -> viewer went away')
+      }
+      reapply(ev)
+    }
+
     window.addEventListener(PF_OBSERVER_EVENT, onObserved)
-    document.addEventListener('visibilitychange', reapply)
+    document.addEventListener('visibilitychange', onVisibility)
     window.addEventListener('focus', reapply)
     window.addEventListener('pageshow', reapply)
     return () => {
       clearTimeout(settle)
       window.removeEventListener(PF_OBSERVER_EVENT, onObserved)
-      document.removeEventListener('visibilitychange', reapply)
+      document.removeEventListener('visibilitychange', onVisibility)
       window.removeEventListener('focus', reapply)
       window.removeEventListener('pageshow', reapply)
     }