fix(client): say when the account's node is elsewhere, and let go of it

Signing in on a desktop links this machine's node to the account, but never
over a key already linked (that would cut off the user's other machine) nor a
node set up for another account. On a real install both left the node reading
"Running" while the hub refused it in a loop, and nothing said why. And the
only way to unlink was the linked machine's own Node page, of no use once
that machine is gone.

- The Node page works out, from the node and the hub each time it looks,
  whether this node can serve the signed-in account (nodeLinkProblem), and
  says why not: "Link this node instead" (asked first) puts this node's key
  on the account; "Use this node for my account" switches a node set up for
  another account through node:start, which takeOver now lets past a node
  that answers "running". The first version went through node:start for
  both, and clicking it on a real install did nothing: a node signed in
  before the account was linked elsewhere answers "running".
- The Profile page unlinks the account's node (DELETE /v1/users/me/node_key),
  from any machine.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

15 files changed, 288 insertions, 4 deletions

diff --git a/packages/meshbay-client/src/main.js b/packages/meshbay-client/src/main.js
index 603dedc..1af4386 100644
--- a/packages/meshbay-client/src/main.js
+++ b/packages/meshbay-client/src/main.js
@@ -2168,8 +2168,11 @@ Its log: ${nodeLogHint()}`);
     // other had just started.
     if (nodeWithAppStart) await nodeWithAppStart.catch(() => {});
     if (nodeEnsuring) await nodeEnsuring.catch(() => {});
+    // `takeOver`: the Node page's "use this node for my account", for a node
+    // set up for another account -- which is running, as that account, and
+    // must be switched and restarted all the same.
     const already = await probeNode();
-    if (already && already.status === 'running') {
+    if (already && already.status === 'running' && !(opts && opts.takeOver)) {
       return { started: true, ...already };
     }
 
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
index c512fe5..1fc734c 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/de.js
@@ -542,6 +542,9 @@ export default {
   'settings.node_key_placeholder': 'Öffentlichen Ed25519-Schlüssel des Nodes einfügen (base64)',
   'settings.node_key_submit': 'Node verknüpfen',
   'settings.node_key_success': 'Node erfolgreich verknüpft',
+  'settings.node_key_unlink': "Trennen",
+  'settings.node_key_unlink_confirm': "Den Node von Ihrem Konto trennen? Er stellt Ihre Gruppen nicht mehr bereit, bis wieder ein Node verknüpft ist.",
+  'settings.node_key_unlinked': "Node getrennt",
   'settings.node_key_current': 'Schlüssel des verknüpften Nodes',
 
   // Sidebar
@@ -951,6 +954,12 @@ export default {
   'node.pair_button': 'Diesen Browser koppeln',
   'node.pair_success': 'Erfolgreich gekoppelt.',
   'node.pair_pending': 'Kopplungscode bereit: Er wird verwendet, wenn Sie das nächste Mal eine Gruppe dieses Nodes öffnen.',
+  'node.link_other_node': "Ihr Konto ist mit dem Node eines anderen Rechners verknüpft, daher kann dieser Node Ihre Gruppen nicht bereitstellen.",
+  'node.link_here': "Stattdessen diesen Node verknüpfen",
+  'node.link_here_confirm': "Diesen Node mit Ihrem Konto verknüpfen? Der derzeit verknüpfte Node auf einem anderen Rechner stellt Ihre Gruppen nicht mehr bereit, bis er erneut verknüpft wird.",
+  'node.link_other_account': "Dieser Node ist für {account} eingerichtet, nicht für Sie, daher kann er Ihre Gruppen nicht bereitstellen.",
+  'node.link_take_over': "Diesen Node für mein Konto verwenden",
+  'node.link_linking': "Verknüpfen…",
   'node.reload': 'Konfiguration neu laden',
   'node.reloaded': 'Konfiguration neu geladen. Verzeichnisänderungen an bestehenden Gruppen sind jetzt aktiv.',
   'node.restart_needed': 'Nach dem Hinzufügen: Gruppenschlüssel initialisieren (meshbay-node gek-init --group <name>).',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
index f5b3808..6f3be87 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/en.js
@@ -530,6 +530,9 @@ export default {
   'settings.node_key_placeholder': 'Paste node Ed25519 public key (base64)',
   'settings.node_key_submit': 'Link Node',
   'settings.node_key_success': 'Node linked successfully',
+  'settings.node_key_unlink': "Unlink",
+  'settings.node_key_unlink_confirm': "Unlink the node from your account? It stops serving your groups until a node is linked again.",
+  'settings.node_key_unlinked': "Node unlinked",
   'settings.node_key_current': 'Linked node key',
 
   // Sidebar
@@ -1093,6 +1096,12 @@ export default {
   'node.pair_button': 'Pair this browser',
   'node.pair_success': 'Paired successfully.',
   'node.pair_pending': "Pairing code ready: it is used the next time you open one of this node's groups.",
+  'node.link_other_node': "Your account is linked to the node of another machine, so this node cannot serve your groups.",
+  'node.link_here': "Link this node instead",
+  'node.link_here_confirm': "Link this node to your account? The node linked now, on another machine, stops serving your groups until it is linked again.",
+  'node.link_other_account': "This node is set up for {account}, not for you, so it cannot serve your groups.",
+  'node.link_take_over': "Use this node for my account",
+  'node.link_linking': "Linking…",
   'node.reload': 'Reload config',
   'node.reloaded': 'Config reloaded. Root changes on existing groups are now active.',
   'node.attach_group': 'Add group',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
index 6e152fb..47490d4 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/es.js
@@ -537,6 +537,9 @@ export default {
   'settings.node_key_placeholder': 'Pegue la clave pública Ed25519 del node (base64)',
   'settings.node_key_submit': 'Vincular el node',
   'settings.node_key_success': 'Node vinculado correctamente',
+  'settings.node_key_unlink': "Desvincular",
+  'settings.node_key_unlink_confirm': "¿Desvincular el nodo de tu cuenta? Dejará de servir tus grupos hasta que se vuelva a vincular un nodo.",
+  'settings.node_key_unlinked': "Nodo desvinculado",
   'settings.node_key_current': 'Clave del node vinculado',
 
   // Sidebar
@@ -945,6 +948,12 @@ export default {
   'node.pair_button': 'Emparejar este navegador',
   'node.pair_success': 'Emparejamiento exitoso.',
   'node.pair_pending': 'Código de emparejamiento listo: se usará la próxima vez que abra uno de los grupos de este Node.',
+  'node.link_other_node': "Tu cuenta está vinculada al nodo de otra máquina, así que este nodo no puede servir tus grupos.",
+  'node.link_here': "Vincular este nodo en su lugar",
+  'node.link_here_confirm': "¿Vincular este nodo a tu cuenta? El nodo vinculado ahora, en otra máquina, dejará de servir tus grupos hasta que se vuelva a vincular.",
+  'node.link_other_account': "Este nodo está configurado para {account}, no para ti, así que no puede servir tus grupos.",
+  'node.link_take_over': "Usar este nodo para mi cuenta",
+  'node.link_linking': "Vinculando…",
   'node.reload': 'Recargar configuración',
   'node.reloaded': 'Configuración recargada. Los cambios de directorios en los grupos existentes ya están activos.',
   'node.restart_needed': 'Después de añadir: inicialice la clave de grupo (meshbay-node gek-init --group <nombre>).',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
index 40c7501..54588b0 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/fr.js
@@ -540,6 +540,9 @@ export default {
   'settings.node_key_placeholder': 'Collez la clé publique Ed25519 du node (base64)',
   'settings.node_key_submit': 'Associer le node',
   'settings.node_key_success': 'Node associé avec succès',
+  'settings.node_key_unlink': "Délier",
+  'settings.node_key_unlink_confirm': "Délier le node de votre compte ? Il cessera de servir vos groupes jusqu'à ce qu'un node soit lié de nouveau.",
+  'settings.node_key_unlinked': "Node délié",
   'settings.node_key_current': 'Clé du node associé',
 
   // Sidebar
@@ -948,6 +951,12 @@ export default {
   'node.pair_button': 'Appairer ce navigateur',
   'node.pair_success': 'Appairage réussi.',
   'node.pair_pending': "Code d'appairage prêt : il sera utilisé à la prochaine ouverture d'un des groupes de ce node.",
+  'node.link_other_node': "Votre compte est lié au node d'une autre machine : ce node-ci ne peut pas servir vos groupes.",
+  'node.link_here': "Lier ce node à la place",
+  'node.link_here_confirm': "Lier ce node à votre compte ? Le node lié actuellement, sur une autre machine, cessera de servir vos groupes jusqu'à ce qu'il soit lié de nouveau.",
+  'node.link_other_account': "Ce node est configuré pour {account}, pas pour vous : il ne peut pas servir vos groupes.",
+  'node.link_take_over': "Utiliser ce node pour mon compte",
+  'node.link_linking': "Liaison…",
   'node.reload': 'Recharger la configuration',
   'node.reloaded': 'Configuration rechargée. Les modifications de répertoires sur les groupes existants sont maintenant actives.',
   'node.restart_needed': 'Après l\'ajout : initialisez la clé de groupe (meshbay-node gek-init --group <name>).',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
index 29a1f5d..5d438a9 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/it.js
@@ -540,6 +540,9 @@ export default {
   'settings.node_key_placeholder': 'Incolli la chiave pubblica Ed25519 del node (base64)',
   'settings.node_key_submit': 'Collega il node',
   'settings.node_key_success': 'Node collegato correttamente',
+  'settings.node_key_unlink': "Scollega",
+  'settings.node_key_unlink_confirm': "Scollegare il node dal tuo account? Smetterà di servire i tuoi gruppi finché non verrà collegato di nuovo un node.",
+  'settings.node_key_unlinked': "Node scollegato",
   'settings.node_key_current': 'Chiave del node collegato',
 
   // Sidebar
@@ -947,6 +950,12 @@ export default {
   'node.pair_button': 'Associa questo browser',
   'node.pair_success': 'Associazione riuscita.',
   'node.pair_pending': 'Codice di associazione pronto: verrà usato la prossima volta che apri uno dei gruppi di questo Node.',
+  'node.link_other_node': "Il tuo account è collegato al node di un'altra macchina, quindi questo node non può servire i tuoi gruppi.",
+  'node.link_here': "Collega invece questo node",
+  'node.link_here_confirm': "Collegare questo node al tuo account? Il node collegato ora, su un'altra macchina, smetterà di servire i tuoi gruppi finché non verrà ricollegato.",
+  'node.link_other_account': "Questo node è configurato per {account}, non per te, quindi non può servire i tuoi gruppi.",
+  'node.link_take_over': "Usa questo node per il mio account",
+  'node.link_linking': "Collegamento…",
   'node.reload': 'Ricarica configurazione',
   'node.reloaded': 'Configurazione ricaricata. Le modifiche alle directory dei gruppi esistenti sono ora attive.',
   'node.restart_needed': "Dopo l'aggiunta: inizializzi la chiave di gruppo (meshbay-node gek-init --group <nome>).",
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
index 4cb4787..1505026 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/ja.js
@@ -534,6 +534,9 @@ export default {
   'settings.node_key_placeholder': 'node の Ed25519 公開鍵を貼り付け（base64）',
   'settings.node_key_submit': 'node を連携',
   'settings.node_key_success': 'node を連携しました',
+  'settings.node_key_unlink': "リンク解除",
+  'settings.node_key_unlink_confirm': "アカウントからノードのリンクを解除しますか？再びノードがリンクされるまで、グループを提供しなくなります。",
+  'settings.node_key_unlinked': "ノードのリンクを解除しました",
   'settings.node_key_current': '連携済みの node 鍵',
 
   // Sidebar
@@ -935,6 +938,12 @@ export default {
   'node.pair_button': 'このブラウザをペアリング',
   'node.pair_success': 'ペアリングに成功しました。',
   'node.pair_pending': 'ペアリングコードの準備ができました。この Node のグループを次に開いたときに使用されます。',
+  'node.link_other_node': "アカウントは別のマシンのノードにリンクされているため、このノードではグループを提供できません。",
+  'node.link_here': "代わりにこのノードをリンク",
+  'node.link_here_confirm': "このノードをアカウントにリンクしますか？現在リンクされている別のマシンのノードは、再びリンクされるまでグループを提供しなくなります。",
+  'node.link_other_account': "このノードはあなたではなく {account} 用に設定されているため、グループを提供できません。",
+  'node.link_take_over': "このノードを自分のアカウントで使う",
+  'node.link_linking': "リンク中…",
   'node.reload': '設定を再読み込み',
   'node.reloaded': '設定を再読み込みしました。既存グループのルート変更が反映されました。',
   'node.restart_needed': '追加後、グループ鍵を初期化してください（meshbay-node gek-init --group <name>）。',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
index 926fadf..858acbf 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/nl.js
@@ -541,6 +541,9 @@ export default {
   'settings.node_key_placeholder': 'Plak de openbare Ed25519-sleutel van de node (base64)',
   'settings.node_key_submit': 'Node koppelen',
   'settings.node_key_success': 'Node gekoppeld',
+  'settings.node_key_unlink': "Ontkoppelen",
+  'settings.node_key_unlink_confirm': "De node van je account ontkoppelen? Hij bedient je groepen niet meer tot er weer een node is gekoppeld.",
+  'settings.node_key_unlinked': "Node ontkoppeld",
   'settings.node_key_current': 'Sleutel van de gekoppelde node',
 
   // Sidebar
@@ -949,6 +952,12 @@ export default {
   'node.pair_button': 'Deze browser koppelen',
   'node.pair_success': 'Succesvol gekoppeld.',
   'node.pair_pending': 'Koppelingscode klaar: die wordt gebruikt zodra u een van de groepen van deze Node opent.',
+  'node.link_other_node': "Je account is gekoppeld aan de node van een andere computer, dus deze node kan je groepen niet bedienen.",
+  'node.link_here': "Koppel in plaats daarvan deze node",
+  'node.link_here_confirm': "Deze node aan je account koppelen? De nu gekoppelde node op een andere computer bedient je groepen niet meer tot hij opnieuw wordt gekoppeld.",
+  'node.link_other_account': "Deze node is ingesteld voor {account}, niet voor jou, dus hij kan je groepen niet bedienen.",
+  'node.link_take_over': "Deze node voor mijn account gebruiken",
+  'node.link_linking': "Koppelen…",
   'node.reload': 'Configuratie herladen',
   'node.reloaded': 'Configuratie herladen. Mapwijzigingen op bestaande groepen zijn nu actief.',
   'node.restart_needed': 'Na het toevoegen: initialiseer de groepssleutel (meshbay-node gek-init --group <naam>).',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
index 2f3a28c..57b4b8a 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/pl.js
@@ -553,6 +553,9 @@ export default {
   'settings.node_key_placeholder': 'Wklej klucz publiczny Ed25519 node (base64)',
   'settings.node_key_submit': 'Powiąż node',
   'settings.node_key_success': 'Node został powiązany',
+  'settings.node_key_unlink': "Odłącz",
+  'settings.node_key_unlink_confirm': "Odłączyć węzeł od twojego konta? Przestanie obsługiwać twoje grupy, dopóki nie zostanie ponownie powiązany węzeł.",
+  'settings.node_key_unlinked': "Węzeł odłączony",
   'settings.node_key_current': 'Klucz powiązanego node',
 
   // Sidebar
@@ -967,6 +970,12 @@ export default {
   'node.pair_button': 'Sparuj tę przeglądarkę',
   'node.pair_success': 'Parowanie zakończone sukcesem.',
   'node.pair_pending': 'Kod parowania gotowy: zostanie użyty przy następnym otwarciu jednej z grup tego Node.',
+  'node.link_other_node': "Twoje konto jest powiązane z węzłem innego komputera, więc ten węzeł nie może obsługiwać twoich grup.",
+  'node.link_here': "Powiąż zamiast tego ten węzeł",
+  'node.link_here_confirm': "Powiązać ten węzeł z twoim kontem? Węzeł powiązany teraz, na innym komputerze, przestanie obsługiwać twoje grupy, dopóki nie zostanie ponownie powiązany.",
+  'node.link_other_account': "Ten węzeł jest skonfigurowany dla {account}, nie dla ciebie, więc nie może obsługiwać twoich grup.",
+  'node.link_take_over': "Użyj tego węzła dla mojego konta",
+  'node.link_linking': "Wiązanie…",
   'node.reload': 'Przeładuj konfigurację',
   'node.reloaded': 'Konfiguracja przeładowana. Zmiany katalogów w istniejących grupach są teraz aktywne.',
   'node.restart_needed': 'Po dodaniu: zainicjalizuj klucz grupy (meshbay-node gek-init --group <nazwa>).',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
index faacbf6..23045fb 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/pt-BR.js
@@ -539,6 +539,9 @@ export default {
   'settings.node_key_placeholder': 'Cole a chave pública Ed25519 do node (base64)',
   'settings.node_key_submit': 'Vincular o node',
   'settings.node_key_success': 'Node vinculado com sucesso',
+  'settings.node_key_unlink': "Desvincular",
+  'settings.node_key_unlink_confirm': "Desvincular o node da sua conta? Ele deixará de servir seus grupos até que um node seja vinculado novamente.",
+  'settings.node_key_unlinked': "Node desvinculado",
   'settings.node_key_current': 'Chave do node vinculado',
 
   // Sidebar
@@ -946,6 +949,12 @@ export default {
   'node.pair_button': 'Parear este navegador',
   'node.pair_success': 'Pareamento realizado com sucesso.',
   'node.pair_pending': 'Código de pareamento pronto: ele será usado na próxima vez que você abrir um dos grupos deste Node.',
+  'node.link_other_node': "Sua conta está vinculada ao node de outra máquina, então este node não pode servir seus grupos.",
+  'node.link_here': "Vincular este node no lugar",
+  'node.link_here_confirm': "Vincular este node à sua conta? O node vinculado agora, em outra máquina, deixará de servir seus grupos até ser vinculado novamente.",
+  'node.link_other_account': "Este node está configurado para {account}, não para você, então não pode servir seus grupos.",
+  'node.link_take_over': "Usar este node na minha conta",
+  'node.link_linking': "Vinculando…",
   'node.reload': 'Recarregar configuração',
   'node.reloaded': 'Configuração recarregada. Alterações de diretórios em grupos existentes estão ativas.',
   'node.restart_needed': 'Após adicionar: inicialize a chave do grupo (meshbay-node gek-init --group <nome>).',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
index 232a4ca..8070b5f 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
@@ -528,6 +528,9 @@ export default {
   'settings.node_key_placeholder': '粘贴 node 的 Ed25519 公钥（base64）',
   'settings.node_key_submit': '关联 node',
   'settings.node_key_success': 'node 关联成功',
+  'settings.node_key_unlink': "取消关联",
+  'settings.node_key_unlink_confirm': "要从你的账户取消关联该节点吗？在再次关联节点之前，它将停止为你的群组提供服务。",
+  'settings.node_key_unlinked': "已取消关联节点",
   'settings.node_key_current': '已关联的 node 密钥',
 
   // Sidebar
@@ -923,6 +926,12 @@ export default {
   'node.pair_button': '配对此浏览器',
   'node.pair_success': '配对成功。',
   'node.pair_pending': '配对码已就绪：下次打开此 Node 的任一群组时将自动使用。',
+  'node.link_other_node': "你的账户已关联到另一台机器的节点，因此此节点无法为你的群组提供服务。",
+  'node.link_here': "改为关联此节点",
+  'node.link_here_confirm': "将此节点关联到你的账户？当前关联的另一台机器上的节点将停止为你的群组提供服务，直到再次关联。",
+  'node.link_other_account': "此节点是为 {account} 而不是为你设置的，因此无法为你的群组提供服务。",
+  'node.link_take_over': "将此节点用于我的账户",
+  'node.link_linking': "正在关联…",
   'node.reload': '重新加载配置',
   'node.reloaded': '配置已重新加载。对现有群组的目录更改现已生效。',
   'node.restart_needed': '添加后请初始化群组密钥（meshbay-node gek-init --group <名称>）。',
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/node-page.js b/packages/meshbay-hub/src/meshbay_hub/static/node-page.js
index 11cd07e..56166c6 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/node-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/node-page.js
@@ -6,7 +6,7 @@ import { t } from './i18n.js';
 import { ask } from './ask.js';
 import * as platform from './platform.js';
 import { Icon } from './icon.js';
-import { HUB, session } from './hub-client.js';
+import { HUB, session, hubFetch } from './hub-client.js';
 
 // ── Node management (D5) ────────────────────────────────────────────────────
 //
@@ -22,6 +22,80 @@ export function pairedFrom(result) {
   return v === true || v === false ? v : null;
 }
 
+// Why this machine's node cannot serve the signed-in account, if it cannot:
+// 'other_account' when it is set up for another account or hub, 'other_node'
+// when the account is linked to another node's key. Signing in links this
+// node (main.js ensureNode) but never over either, since that would cut off
+// the user's other machine or someone else's node; both left a node reading
+// "Running" that the hub refused in a loop, with nothing here saying why
+// (found on a real install, 2026-10-10). Worked out from the node and the hub
+// each time the page looks, not kept from sign-in: a link made or removed on
+// the Profile page or on the other machine changes the answer.
+export function nodeLinkProblem(info, linkedKey, username, hub) {
+  if (!info || !username) return null;
+  const sameHub = (a, b) => String(a || '').replace(/\/+$/, '') === String(b || '').replace(/\/+$/, '');
+  if ((info.username && info.username !== username)
+      || (info.hub_url && hub && !sameHub(info.hub_url, hub))) return 'other_account';
+  if (linkedKey && info.pk_node_ed25519 && linkedKey !== info.pk_node_ed25519) return 'other_node';
+  return null;
+}
+
+function NodeLinkBanner({ info, token, username, onLinked }) {
+  const [linkedKey, setLinkedKey] = useState(null);
+  const [busy, setBusy] = useState(false);
+  const [err, setErr] = useState('');
+  const nodeKey = info && info.pk_node_ed25519;
+
+  useEffect(() => {
+    if (!username || !token) return;
+    let cancelled = false;
+    hubFetch(`/v1/users/${encodeURIComponent(username)}/pubkeys`, { token })
+      .then((k) => { if (!cancelled) setLinkedKey((k && k.pk_node_ed25519) || null); })
+      .catch(() => {});
+    return () => { cancelled = true; };
+  }, [username, token, nodeKey]);
+
+  const problem = nodeLinkProblem(info, linkedKey, username, HUB);
+  if (!problem) return null;
+
+  // Another node's key: this node's replaces it on the account, and a node
+  // waiting for its account signs in on its next attempt. Not node:start,
+  // which leaves a node that answers "running" alone, and one can (signed in
+  // before the account was linked elsewhere). Another account: node:start
+  // switches it, after asking, restarts it and links it.
+  const takeOver = async () => {
+    if (problem === 'other_node' && !await ask(t('node.link_here_confirm'))) return;
+    setBusy(true);
+    setErr('');
+    try {
+      if (problem === 'other_node') {
+        await hubFetch('/v1/users/me/node_key', {
+          method: 'PUT', token, body: { pk_node_ed25519: nodeKey },
+        });
+      } else {
+        await platform.node.start({ hubUrl: HUB, username, token, takeOver: true });
+      }
+      setLinkedKey(nodeKey);
+      if (onLinked) onLinked();
+    } catch (e) {
+      setErr(platform.bridgeMessage(e));
+    } finally {
+      setBusy(false);
+    }
+  };
+
+  return html`
+    <div class="node-pair-banner node-link-banner">
+      <p>${problem === 'other_node'
+        ? t('node.link_other_node')
+        : t('node.link_other_account', { account: `${info.username} @ ${info.hub_url}` })}</p>
+      <button class="btn btn-primary btn-small" disabled=${busy} onClick=${takeOver}>
+        ${busy ? t('node.link_linking')
+          : problem === 'other_node' ? t('node.link_here') : t('node.link_take_over')}</button>
+      ${err && html`<p class="error-msg">${err}</p>`}
+    </div>`;
+}
+
 function NodeServicePanel({ onChanged, token, username }) {
   const [info, setInfo] = useState(null);
   const [busy, setBusy] = useState('');
@@ -725,6 +799,8 @@ export function NodePage({ groups, token, username }) {
           ${t('node.reload')}</button>
       </div>
       <${NodeServicePanel} onChanged=${fetchStatus} token=${token} username=${username} />
+      <${NodeLinkBanner} info=${nodeInfo} token=${token} username=${username}
+        onLinked=${fetchStatus} />
       ${actionMsg && html`<div class="node-message">${actionMsg}</div>`}
       ${operatorPaired === false && nodeGroups.length > 0 && html`
         <div class="node-pair-banner">
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js b/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js
index aac3c14..b52a8c6 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js
@@ -370,6 +370,25 @@ export function ProfilePage({ user, onLogout }) {
     }
   }, [nodeKey, user.token]);
 
+  // Unlinking was only on the linked machine's own Node page, so an account
+  // whose node was on a machine since wiped or lost had no way out here; and a
+  // new machine's node will not take over a key that is still linked
+  // (main.js ensureNode). The hub accepts it from any session of the account.
+  const unlinkNodeKey = useCallback(async () => {
+    if (!await ask(t('settings.node_key_unlink_confirm'))) return;
+    setNodeKeyLoading(true);
+    setNodeKeyStatus('');
+    try {
+      await hubFetch('/v1/users/me/node_key', { method: 'DELETE', token: user.token });
+      setCurrentNodeKey(null);
+      setNodeKeyStatus(t('settings.node_key_unlinked'));
+    } catch (e) {
+      setNodeKeyStatus(e.message);
+    } finally {
+      setNodeKeyLoading(false);
+    }
+  }, [user.token]);
+
   return html`
     <div>
       <h2>${t('profile.title')}</h2>
@@ -435,6 +454,9 @@ export function ProfilePage({ user, onLogout }) {
           <div class="settings-row" style="margin-top:8px">
             <span class="settings-label">${t('settings.node_key_current')}</span>
             <code class="settings-value" style="font-size:0.8em;word-break:break-all">${currentNodeKey}</code>
+            <button class="admin-btn" onClick=${unlinkNodeKey} disabled=${nodeKeyLoading}>
+              ${t('settings.node_key_unlink')}
+            </button>
           </div>
         `}
         <div style="display:flex;gap:8px;margin-top:10px;align-items:center">
@@ -448,7 +470,7 @@ export function ProfilePage({ user, onLogout }) {
           </button>
         </div>
         ${nodeKeyStatus && html`
-          <p style="margin-top:6px;font-size:0.85em;color:${nodeKeyStatus === t('settings.node_key_success') ? 'var(--success)' : 'var(--error)'}">
+          <p style="margin-top:6px;font-size:0.85em;color:${[t('settings.node_key_success'), t('settings.node_key_unlinked')].includes(nodeKeyStatus) ? 'var(--success)' : 'var(--error)'}">
             ${nodeKeyStatus}
           </p>
         `}
diff --git a/packages/meshbay-hub/tests/test_node_link_banner.py b/packages/meshbay-hub/tests/test_node_link_banner.py
new file mode 100644
index 0000000..eef29bf
--- /dev/null
+++ b/packages/meshbay-hub/tests/test_node_link_banner.py
@@ -0,0 +1,93 @@
+"""
+A node that cannot serve the signed-in account says so, and the account can
+let go of a node from anywhere.
+
+Signing in on a desktop links this machine's node to the account (main.js
+`ensureNode`), but never over a key already linked -- that would cut off the
+user's other machine -- nor a node set up for another account. Found on a real
+install (2026-10-10): the node read "Running" while the hub refused it in a
+loop, and nothing said why. And the only way to unlink was the linked
+machine's own Node page, of no use once that machine is gone.
+"""
+
+import json
+import re
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+STATIC = Path(__file__).resolve().parents[1] / "src" / "meshbay_hub" / "static"
+NODE_PAGE = STATIC / "node-page.js"
+PROFILE_PAGE = STATIC / "profile-page.js"
+
+
+def _src(path: Path) -> str:
+    return path.read_text(encoding="utf-8")
+
+
+@pytest.mark.skipif(shutil.which("node") is None, reason="node is not available")
+def test_the_problem_is_worked_out_from_the_node_and_the_hub(tmp_path):
+    m = re.search(r"^export function nodeLinkProblem\(.*?^\}", _src(NODE_PAGE), re.M | re.S)
+    assert m, "node-page.js no longer has nodeLinkProblem"
+    mine = {"username": "alice", "hub_url": "https://hub.example/", "pk_node_ed25519": "K1"}
+    cases = [
+        [mine, "K1", "alice", "https://hub.example"],          # linked here: fine
+        [mine, None, "alice", "https://hub.example"],          # nothing linked: sign-in links it
+        [mine, "K2", "alice", "https://hub.example"],          # another node's key
+        [{**mine, "username": "bob"}, "K1", "alice", "https://hub.example"],
+        [mine, "K1", "alice", "https://other.example"],        # set up for another hub
+        [mine, "K2", "alice", ""],                             # browser: same-origin hub
+        [None, "K2", "alice", "https://hub.example"],          # node not answering
+    ]
+    script = tmp_path / "case.js"
+    script.write_text(
+        m.group(0).replace("export ", "")
+        + f"\nconsole.log(JSON.stringify({json.dumps(cases)}"
+          ".map(c => nodeLinkProblem(...c))));",
+        encoding="utf-8")
+    out = subprocess.run(["node", str(script)], capture_output=True, encoding="utf-8", check=True)
+    assert json.loads(out.stdout) == [
+        None, None, "other_node", "other_account", "other_account", "other_node", None]
+
+
+def test_the_node_page_shows_the_banner_and_offers_the_link():
+    src = _src(NODE_PAGE)
+    page = src.split("export function NodePage(", 1)[1]
+    assert "<${NodeLinkBanner} info=${nodeInfo} token=${token} username=${username}" in page
+    banner = src.split("function NodeLinkBanner(", 1)[1].split("\nfunction ", 1)[0]
+    # Asked of the hub, not remembered from sign-in.
+    assert "hubFetch(`/v1/users/${encodeURIComponent(username)}/pubkeys`" in banner
+    assert "nodeLinkProblem(info, linkedKey, username, HUB)" in banner
+    take_over = banner.split("const takeOver = async () => {", 1)[1].split("\n  };", 1)[0]
+    # Replacing another machine's link is asked first, then this node's key
+    # replaces it directly: node:start left a node answering "running" alone,
+    # and a node signed in before the account was linked elsewhere does
+    # (found clicking it on a real install). For another account node:start
+    # asks itself before switching, and takeOver gets past "running".
+    assert "problem === 'other_node' && !await ask(t('node.link_here_confirm'))" in take_over
+    assert "method: 'PUT', token, body: { pk_node_ed25519: nodeKey }" in take_over
+    assert "platform.node.start({ hubUrl: HUB, username, token, takeOver: true })" in take_over
+    for key in ("node.link_other_node", "node.link_other_account", "node.link_here",
+                "node.link_take_over", "node.link_linking"):
+        assert f"'{key}'" in banner, key
+
+
+def test_node_start_switches_a_running_node_when_asked_to_take_it_over():
+    main_js = (Path(__file__).resolve().parents[3] / "packages" / "meshbay-client" / "src"
+               / "main.js").read_text(encoding="utf-8")
+    start = main_js.split("handle('node:start', async (_e, opts) => {", 1)[1]
+    start = start.split("\n  });\n", 1)[0]
+    assert "already.status === 'running' && !(opts && opts.takeOver)" in start
+
+
+def test_the_profile_page_can_unlink_the_node():
+    src = _src(PROFILE_PAGE)
+    unlink = src.split("const unlinkNodeKey = useCallback(async () => {", 1)[1].split("}, [", 1)[0]
+    assert "if (!await ask(t('settings.node_key_unlink_confirm'))) return;" in unlink
+    assert "hubFetch('/v1/users/me/node_key', { method: 'DELETE', token: user.token })" in unlink
+    assert "setCurrentNodeKey(null)" in unlink
+    # Offered only where there is a key to let go of.
+    shown = src.split("${currentNodeKey && html`", 1)[1].split("`}", 1)[0]
+    assert "onClick=${unlinkNodeKey}" in shown
diff --git a/packages/meshbay-hub/tests/test_node_page_pairing.py b/packages/meshbay-hub/tests/test_node_page_pairing.py
index c716e0a..ac77356 100644
--- a/packages/meshbay-hub/tests/test_node_page_pairing.py
+++ b/packages/meshbay-hub/tests/test_node_page_pairing.py
@@ -56,7 +56,7 @@ def test_pair_this_browser_queues_the_code_instead_of_claiming_success():
     pair = src.split("const doPairOperator = useCallback(", 1)[1].split("}, [refresh]);", 1)[0]
     assert "session.pendingJoinCode = result.code;" in pair
     assert "setOperatorPaired(true)" not in pair
-    assert "import { HUB, session } from './hub-client.js';" in src
+    assert re.search(r"import \{ HUB, session(, \w+)* \} from './hub-client.js';", src)
 
 
 def test_no_pairing_banner_for_a_node_with_no_group_yet():