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>

1 files changed, 77 insertions, 1 deletions

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">