DEBUG: instrument view rebuilds and depth re-apply on refocus

Temporary. Row grouping re-expands whenever the browser regains focus, for
both the toolbar EXPAND buttons and the per-row +/-. set_depth() and
per-node expansion both live on the view rather than in ViewConfig, so a
rebuilt view loses them -- but nothing so far distinguishes "the view was
rebuilt" from "the re-apply lost its race with the redraw".

Tags each view object with an id via a WeakMap and logs it at every point
that could rebuild one: focus/visibilitychange/pageshow, config-update,
applyDepth, the theme effect, and initViewer. A changed id across a refocus
means the view was discarded; an unchanged id means the depth re-apply
itself is at fault. Each bail-out in the refocus handler now says which
branch it took, which also shows whether expandDepthRef was ever set.

Prefix [pf-depth]. Revert this commit once the cause is known.

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

ui/src/views/Forecast.jsx

@@ -202,19 +202,69 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   // Intersection/ResizeObserver triggers when you switch back to the tab — and the
   // 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.
+  const viewSeqRef = useRef(0)
+  const viewIdsRef = useRef(new WeakMap())
+  const lastViewIdRef = useRef(null)
+
+  function dbg(msg, extra) {
+    const t = new Date().toISOString().slice(11, 23)
+    if (extra !== undefined) console.log(`[pf-depth ${t}] ${msg}`, extra)
+    else                     console.log(`[pf-depth ${t}] ${msg}`)
+  }
+
+  function viewId(v) {
+    if (!v) return 'none'
+    if (!viewIdsRef.current.has(v)) viewIdsRef.current.set(v, ++viewSeqRef.current)
+    return '#' + viewIdsRef.current.get(v)
+  }
+
+  // Read the viewer's current view and report whether it is the same object we
+  // saw last time. A changed id means the view was discarded and rebuilt.
+  async function probeView(where) {
+    const viewer = viewerRef.current
+    if (!viewer) return dbg(`probe(${where}): no viewer`)
+    try {
+      const v  = await viewer.getView()
+      const id = viewId(v)
+      const changed = lastViewIdRef.current !== null && lastViewIdRef.current !== id
+      dbg(`probe(${where}): view ${id}${changed ? `  <-- REBUILT (was ${lastViewIdRef.current})` : ''}`)
+      lastViewIdRef.current = id
+    } catch (err) { dbg(`probe(${where}) threw`, err) }
+  }
+  // -------------------------------------------------------------- END DEBUG
+
   useEffect(() => {
     let queued = false
-    const reapply = () => {
-      if (document.visibilityState !== 'visible') return
-      if (expandDepthRef.current == null || !viewerRef.current) return
-      if (queued) return
+    const reapply = async (ev) => {
+      dbg(`event ${ev?.type || '?'}`, {
+        visibility: document.visibilityState,
+        expandDepthRef: expandDepthRef.current,
+        hasViewer: !!viewerRef.current,
+      })
+      // Probe the view identity before touching anything: if the id has changed
+      // since the last log line, the viewer rebuilt its view and that is where
+      // the depth went, rather than the re-apply below losing a race.
+      await probeView('on ' + (ev?.type || '?'))
+
+      if (document.visibilityState !== 'visible') return dbg('bail: not visible')
+      if (!viewerRef.current)                      return dbg('bail: no viewer')
+      if (expandDepthRef.current == null)          return dbg('bail: no depth recorded (toolbar EXPAND never used, or per-node +/- only)')
+      if (queued)                                  return dbg('bail: already queued')
       queued = true
       // let the viewer finish its own redraw first, or it will draw over us
       requestAnimationFrame(() => setTimeout(async () => {
         queued = false
         const d = expandDepthRef.current
-        if (d == null) return
-        try { await applyDepth(d) } catch {}
+        if (d == null) return dbg('re-apply aborted: depth became null')
+        try {
+          await applyDepth(d)
+          dbg(`re-apply done depth=${d}`)
+        } catch (err) { dbg('re-apply THREW', err) }
       }, 60))
     }
     document.addEventListener('visibilitychange', reapply)
@@ -370,6 +420,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
 
   useEffect(() => {
     if (viewerRef.current) {
+      dbg(`theme effect -> ${dark ? 'Pro Dark' : 'Pro Light'} (a theme change rebuilds the view)`)
       viewerRef.current.setAttribute('theme', dark ? 'Pro Dark' : 'Pro Light')
     }
   }, [dark, versionId])
@@ -575,6 +626,7 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
   async function initViewer(vid, sid) {
     const viewer = viewerRef.current
     if (!viewer) return
+    dbg(`initViewer(version=${vid}, source=${sid}) -- FULL RELOAD, depth reset to null`)
     const myId = ++initIdRef.current
     setLoading(true)
     setLargeDataset(false)
@@ -677,6 +729,8 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
       // auto-persist viewer state (formatting, columns, etc.) to the last-used cache
       if (viewer._pspUpdate) viewer.removeEventListener('perspective-config-update', viewer._pspUpdate)
       viewer._pspUpdate = async () => {
+        dbg(`perspective-config-update (collapsing=${collapsingRef.current})`)
+        await probeView('config-update')
         try {
           // A split_by change that is not ours is the user rearranging the pivot, and
           // it redefines the hierarchy. Ours is a collapse, and must not overwrite it.
@@ -787,6 +841,8 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
     const viewer = viewerRef.current
     if (!viewer) return
     const view   = await viewer.getView()
+    dbg(`applyDepth(${d}) on view ${viewId(view)}`)
+    lastViewIdRef.current = viewId(view)
     await view.set_depth(d)
     const plugin = await viewer.getPlugin()
     await plugin.draw(view)