Bug bash 5: the URL, the fleet loop, and an empty card

A link to a hub page no longer reloads onto the last machine; a link from a hub-only page to
a machine's page arrives at that page; a page being left no longer asks about the next page's
selection; the hub holds its machines to the rate it is itself running.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/src/hashsel.ts

@@ -2,20 +2,26 @@
 // which unit, which job, which folder. Reload keeps it and a link can carry it.
 import { useCallback, useEffect, useState } from 'react'
 
-const read = () => { try { return decodeURIComponent(location.hash.split('/').slice(3).join('/')) } catch { return '' } }
+const viewOf = () => location.hash.split('/')[2] ?? ''
+// The selection belongs to one page. A page reads it only while the URL is still pointing at
+// that page: moving from #/grid/services/ssh.service to #/hub/docker/stack:gitea changes the
+// hash in one step, and the page being left is still mounted for a moment — long enough, before
+// this, for Services to go and ask grid about a "service" called stack:gitea.
+const read = (view?: string) => { try { return view !== undefined && viewOf() !== view ? '' : decodeURIComponent(location.hash.split('/').slice(3).join('/')) } catch { return '' } }
 
-export function useHashSel(): [string, (v: string) => void] {
-  const [sel, setSel] = useState(read)
+export function useHashSel(view?: string): [string, (v: string) => void] {
+  const [sel, setSel] = useState(() => read(view))
   useEffect(() => {
-    const h = () => setSel(read())
+    const h = () => setSel(read(view))
     window.addEventListener('popstate', h); window.addEventListener('hashchange', h)
     return () => { window.removeEventListener('popstate', h); window.removeEventListener('hashchange', h) }
-  }, [])
+  }, [view])
   const set = useCallback((v: string) => {
+    if (view !== undefined && viewOf() !== view) return // the URL has already moved on
     const base = location.hash.split('/').slice(0, 3).join('/')
     const want = v ? `${base}/${encodeURIComponent(v)}` : base
     if (location.hash !== want) history.replaceState(null, '', want)
     setSel(v)
-  }, [])
+  }, [view])
   return [sel, set]
 }