diff --git a/CLAUDE.md b/CLAUDE.md
index 9591095..fe773dc 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -112,7 +112,10 @@ Theme state lives in `ui/src/theme.jsx` — a React context (`ThemeContext`) wit
 - Operation panel (Scale/Recode/Clone) SQL generation and dim_period JOIN are complete; UI wiring to API still needs completion
 - Load progress bar is jittery — needs throttle (~10 updates/sec)
 - Default pivot layout should be configurable per source (currently hardcodes first 2 dimensions)
-- Source/version selection doesn't persist across page reload
+- Source/version selection persists in `localStorage` (`pf_sourceId` / `pf_versionId`,
+  `App.jsx`). It is re-validated against the live list whenever that list changes, so a
+  deregistered source or deleted version re-points at the first remaining one instead of
+  leaving a dead id that 404s every call
 - Col_meta / version schema drift: if col_meta roles change after a version's forecast table is created, SQL and DDL go out of sync — workaround is to delete and recreate the version
 
 ## Deferred (not in v1)
diff --git a/ui/src/App.jsx b/ui/src/App.jsx
index 1ed8ba1..64021e6 100644
--- a/ui/src/App.jsx
+++ b/ui/src/App.jsx
@@ -10,6 +10,7 @@ export default function App() {
   const [sidebarExpanded, setSidebarExpanded] = useState(() => localStorage.getItem('pf_sidebar') !== 'collapsed')
 
   const [sources,   setSources]   = useState([])
+  const [sourcesLoaded, setSourcesLoaded] = useState(false)
   const [sourceId,  setSourceId]  = useState(() => localStorage.getItem('pf_sourceId')  || '')
   const [versions,  setVersions]  = useState([])
   const [versionId, setVersionId] = useState(() => localStorage.getItem('pf_versionId') || '')
@@ -21,37 +22,49 @@ export default function App() {
 
   const refreshSources = useCallback(async () => {
     const data = await fetch('/api/sources').then(r => r.json())
-    setSources(data)
-    return data
+    const list = Array.isArray(data) ? data : []
+    setSources(list)
+    setSourcesLoaded(true)
+    return list
   }, [])
 
   const refreshVersions = useCallback(async (sid) => {
     const id = sid ?? sourceId
     if (!id) { setVersions([]); return [] }
     const data = await fetch(`/api/sources/${id}/versions`).then(r => r.json())
-    setVersions(data)
-    return data
+    const list = Array.isArray(data) ? data : []
+    setVersions(list)
+    return list
   }, [sourceId])
 
+  useEffect(() => { refreshSources() }, [])
+
+  // The selection is restored from localStorage and survives a deregister, so it
+  // has to be re-checked against the list itself rather than only at mount:
+  // deleting the selected source otherwise leaves a dead id behind and every
+  // call 404s "Source not found" until the page is reloaded.
   useEffect(() => {
-    refreshSources().then(data => {
-      if (data.length === 0) { setSourceId(''); return }
-      if (!sourceId || !data.some(s => String(s.id) === String(sourceId))) {
-        setSourceId(String(data[0].id))
-      }
-    })
-  }, [])
+    if (!sourcesLoaded) return
+    if (sources.length === 0) { setSourceId(''); return }
+    if (!sourceId || !sources.some(s => String(s.id) === String(sourceId))) {
+      setSourceId(String(sources[0].id))
+    }
+  }, [sources, sourcesLoaded, sourceId])
 
   useEffect(() => {
     if (!sourceId) { setVersions([]); setVersionId(''); return }
-    refreshVersions(sourceId).then(data => {
-      if (data.length === 0) { setVersionId(''); return }
-      if (!versionId || !data.some(v => String(v.id) === String(versionId))) {
-        setVersionId(String(data[0].id))
-      }
-    })
+    refreshVersions(sourceId)
   }, [sourceId])
 
+  // Same reasoning as sources: a deleted version must not stay selected.
+  useEffect(() => {
+    if (!sourceId) return
+    if (versions.length === 0) { setVersionId(''); return }
+    if (!versionId || !versions.some(v => String(v.id) === String(versionId))) {
+      setVersionId(String(versions[0].id))
+    }
+  }, [versions, sourceId, versionId])
+
   const ctx = {
     sources, sourceId, setSourceId,
     versions, versionId, setVersionId,