Wait for the viewer's table before re-applying row depth on refocus

The instrumentation showed the re-apply mostly throwing "No table set": the
viewer is detached from its table for a while after a refocus, the fixed
60ms delay fired inside that window, set_depth threw, and the tree rendered
fully expanded. The handful of times the delay happened to be long enough,
the log reads "re-apply done depth=0" and the collapse survived.

So poll for the table instead of guessing, up to 5s. queued now clears in a
finally after the work rather than at the top of the callback, so the focus
and visibilitychange that both fire for one window switch no longer each
run a re-apply -- that was the doubled applyDepth in the log.

Does not address per-node +/- collapse, which is still not recorded at all:
expandDepthRef stays null because only the toolbar buttons set it, and the
view exposes expand()/collapse() with no getter to read the state back.

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

ui/src/views/Forecast.jsx

@@ -236,6 +236,26 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
       lastViewIdRef.current = id
     } catch (err) { dbg(`probe(${where}) threw`, err) }
   }
+  // The viewer is briefly detached from its table around a refocus, and anything
+  // touching the view in that window throws "No table set". Poll until it is back
+  // rather than guessing at a delay.
+  async function waitForTable(deadlineMs = 5000, stepMs = 60) {
+    const started = Date.now()
+    let attempts = 0
+    while (Date.now() - started < deadlineMs) {
+      attempts++
+      try {
+        const viewer = viewerRef.current
+        if (viewer && await viewer.getTable()) {
+          if (attempts > 1) dbg(`table re-attached after ${attempts} polls / ${Date.now() - started}ms`)
+          return true
+        }
+      } catch { /* not yet */ }
+      await new Promise(r => setTimeout(r, stepMs))
+    }
+    return false
+  }
+
   // -------------------------------------------------------------- END DEBUG
 
   useEffect(() => {
@@ -256,16 +276,25 @@ export default function Forecast({ sources = [], sourceId, versions = [], versio
       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
+      // 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
+      // viewer is detached from its table for a while after a refocus, and
+      // set_depth on a detached viewer throws "No table set" and the tree renders
+      // fully expanded. queued stays set until the work is done, so a focus and a
+      // visibilitychange for the same switch don't both re-apply.
+      requestAnimationFrame(async () => {
+        try {
           const d = expandDepthRef.current
           if (d == null) return dbg('re-apply aborted: depth became null')
-        try {
+          if (!(await waitForTable())) return dbg('re-apply gave up: viewer never re-attached a table')
           await applyDepth(d)
           dbg(`re-apply done depth=${d}`)
-        } catch (err) { dbg('re-apply THREW', err) }
-      }, 60))
+        } catch (err) {
+          dbg('re-apply THREW', err)
+        } finally {
+          queued = false
+        }
+      })
     }
     document.addEventListener('visibilitychange', reapply)
     window.addEventListener('focus', reapply)