Land a paired panel on its own screen instead of a new code

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013Gf7WaExcJ9bs3kfJXB3nK

frontend/src/routes/panel.index.tsx

@@ -1,12 +1,32 @@
 import { useMutation, useQuery } from "@tanstack/react-query"
-import { createFileRoute } from "@tanstack/react-router"
+import { createFileRoute, redirect } from "@tanstack/react-router"
 import { Check, Copy } from "lucide-react"
 import { useEffect } from "react"
 
 import { ApiError, PanelsService } from "@/client"
 import { Button } from "@/components/ui/button"
 import { useCopyToClipboard } from "@/hooks/useCopyToClipboard"
-import { appPath, isPortal, openPortalSession } from "@/lib/portal"
+import { apiToken, appPath, isPortal, openPortalSession } from "@/lib/portal"
+
+/**
+ * The panel a credential in hand names, or "" when it names none.
+ *
+ * A panel token carries the panel it was minted for; a user token and a
+ * malformed one both mean "not an adopted screen". Read rather than verified:
+ * this only decides where to send the browser, and the server still judges the
+ * credential on the first call it makes there.
+ */
+function pairedPanel(): string {
+  try {
+    const [, payload] = apiToken().split(".")
+    const claims = JSON.parse(
+      atob(payload.replace(/-/g, "+").replace(/_/g, "/")),
+    )
+    return typeof claims.panel === "string" ? claims.panel : ""
+  } catch {
+    return ""
+  }
+}
 
 /**
  * Adopting a screen that has no keyboard.
@@ -16,6 +36,10 @@ import { appPath, isPortal, openPortalSession } from "@/lib/portal"
  * code into the panels dialog to say which panel this device is, and the
  * credential it mints arrives here on the next poll.
  *
+ * Only once, though: a screen that already holds a credential goes straight to
+ * the panel it names, so a reboot comes back to the dashboard rather than
+ * asking the household for another code.
+ *
  * Outside both shells like `/view/{name}`: until it is paired, this device has
  * no session and there is nothing to put around it.
  *
@@ -26,6 +50,13 @@ import { appPath, isPortal, openPortalSession } from "@/lib/portal"
  */
 export const Route = createFileRoute("/panel/")({
   component: PairPanel,
+  beforeLoad: () => {
+    // Nothing to mint a code for. A credential the server has since stopped
+    // honouring comes back here with storage cleared, so the next arrival
+    // pairs normally rather than bouncing.
+    const paired = pairedPanel()
+    if (paired) throw redirect({ to: "/panel/$id", params: { id: paired } })
+  },
   head: () => ({ meta: [{ title: "Pair this panel - Fluksio" }] }),
 })