fix(web): hand the new heartbeat token over in sessionStorage, not the URL

web/app/(app)/monitors/[id]/page.tsx

@@ -2,7 +2,7 @@
 
 import { useEffect, useState } from "react";
 import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
-import { useParams, useRouter, useSearchParams } from "next/navigation";
+import { useParams, useRouter } from "next/navigation";
 import Link from "next/link";
 import { api, Incident, Rollup } from "@/lib/api";
 import { Button, ConfirmDialog, friendlyMessage, useToast } from "@/components/ui";
@@ -322,7 +322,6 @@ function Row({ label, value }: { label: string; value: React.ReactNode }) {
 export default function MonitorDetailPage() {
     const params = useParams();
     const router = useRouter();
-    const searchParams = useSearchParams();
     const queryClient = useQueryClient();
     const monitorId = params.id as string;
     const [confirmDelete, setConfirmDelete] = useState(false);
@@ -330,19 +329,21 @@ export default function MonitorDetailPage() {
     const [range, setRange] = useState<Range>(RANGES[0]);
     const toast = useToast();
 
-    /* The token is only ever handed back once, on the create response, riding
-       in the query string for this one navigation. Keep it in state and strip
-       the query immediately so a reload, a bookmark or browser history never
-       holds it. */
+    /* The token is only ever handed back once, on the create response. The
+       create page parks it in sessionStorage for this one navigation, because a
+       query string would reach proxy access logs. Read it once and remove it
+       straight away so a reload or another tab never shows it again. */
     const [heartbeatToken, setHeartbeatToken] = useState<string | null>(null);
     useEffect(() => {
-        const t = searchParams.get("token");
-        if (t) {
-            setHeartbeatToken(t);
-            router.replace(`/monitors/${monitorId}`);
+        const key = `vantage:hbtoken:${monitorId}`;
+        try {
+            const t = sessionStorage.getItem(key);
+            sessionStorage.removeItem(key);
+            if (t) setHeartbeatToken(t);
+        } catch {
+            // Storage blocked: nothing was handed over.
         }
-        // eslint-disable-next-line react-hooks/exhaustive-deps
-    }, []);
+    }, [monitorId]);
 
     const { data: monitor, isLoading } = useQuery({
         queryKey: ["monitors", monitorId],

web/app/(app)/monitors/new/page.tsx

@@ -24,11 +24,16 @@ export default function NewMonitorPage() {
             // survive the route change, which is the one thing an inline
             // banner on the form cannot do. The error stays on the form.
             toast.success(`Created ${m.name}. First check runs within its interval.`);
+            // The token is shown once. Hand it over in memory, never in the
+            // URL: the RSC fetch for a query string lands in proxy access logs.
             if (m.heartbeat_token) {
-                router.push(`/monitors/${m.monitor_id}?token=${encodeURIComponent(m.heartbeat_token)}`);
-            } else {
-                router.push(`/monitors/${m.monitor_id}`);
+                try {
+                    sessionStorage.setItem(`vantage:hbtoken:${m.monitor_id}`, m.heartbeat_token);
+                } catch {
+                    // Storage blocked: the user can rotate to get a token.
+                }
             }
+            router.push(`/monitors/${m.monitor_id}`);
         },
     });