feat(theseus/error): offline banner + BCNR did-you-mean on typos

Two problems bundled into the branded error page:

1) "fetch failed" on no network — the tab kept falling through to
   name-not-registered (and other "we asked and got nothing" verdicts)
   because a totally offline browser can't reach the beacon to know.
   Add a first-class `offline` kind that runs before every other
   verdict: navigator.onLine === false wins; the page says "You appear
   to be offline" and keeps the address so the user can Retry after
   reconnecting.

2) Typos on BCNR names (games.x when they meant game.x) — the page
   only offered Search / Register. Now the page asks main for the top
   near-matches from the warm sharedIndex (Levenshtein ≤ 2, same TLD)
   over an origin-gated `error-bns-similar` IPC. Up to three matches
   render as chip-links; clicking one retries at that host, preserving
   the original path. Works offline too — the index is local.

Origin-gate on the IPC uses the existing isErrorPageSender check, and
error-preload.js exposes only the invoke — no arbitrary index access.

error-preload.js

@@ -8,4 +8,5 @@ contextBridge.exposeInMainWorld("errorpage", {
   searchFor:  (text) => ipcRenderer.invoke("error-search", text),
   registerOnSirius: (host) => ipcRenderer.invoke("error-register", host),
   openExternal:     (url)  => ipcRenderer.invoke("error-open-external", url),
+  bnsSimilar:       (host) => ipcRenderer.invoke("error-bns-similar", host),
 });

error.html

@@ -37,6 +37,14 @@
   .tried .t { display: flex; gap: 8px; align-items: center; padding: 3px 0; }
   .tried .t .m { width: 12px; text-align: center; color: var(--err); }
   .tried .t .m.ok { color: var(--acid) }
+  .suggest { margin: 1rem 0 0; padding: 12px 14px; background: var(--panel2);
+             border: 1px solid rgba(214,255,61,.25); border-radius: 10px; font-size: 13px; color: var(--ink); }
+  .suggest .lbl { color: var(--mut); font-size: 12px; margin-bottom: 6px; }
+  .suggest .row { display: flex; flex-wrap: wrap; gap: 6px 8px; }
+  .suggest a { display: inline-flex; align-items: center; gap: 6px; padding: 4px 10px; border-radius: 6px;
+               background: var(--panel); border: 1px solid var(--line); color: var(--acid);
+               font-family: ui-monospace, monospace; font-size: 12.5px; text-decoration: none; cursor: pointer; }
+  .suggest a:hover { border-color: rgba(214,255,61,.55); filter: brightness(1.05); }
   .actions { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 1.3rem; }
   .btn { font-family: inherit; font-size: 13.5px; padding: 9px 16px; border-radius: 9px;
          border: 1px solid var(--line); background: var(--panel2); color: var(--ink);
@@ -67,6 +75,11 @@
     <div class="t"><span class="m">✕</span> <span>Clearnet DNS — no host at this name either</span></div>
   </div>
 
+  <div class="suggest" id="suggest" hidden>
+    <div class="lbl">Did you mean</div>
+    <div class="row" id="suggestRow"></div>
+  </div>
+
   <div class="actions" id="actions"></div>
 
   <div class="details">
@@ -77,12 +90,19 @@
 
 <script>
   const q = new URLSearchParams(location.search);
-  const kind = q.get("kind") || "generic";     // name-not-registered | name-unreachable | unreachable | tls | generic
+  let   kind = q.get("kind") || "generic";     // offline | name-not-registered | name-unreachable | unreachable | tls | generic
   const host = q.get("host") || "";
   const url  = q.get("url")  || "";
   const code = q.get("code") || "";
   const desc = q.get("desc") || "";
 
+  // Offline is a special case: if the browser process itself has no
+  // network, every load will fail here and we'd otherwise mis-report
+  // BCNR-eligible names as "not registered" (we couldn't reach the
+  // beacon to know). Detect it up front so the user sees a clear
+  // "you're offline" instead of a false verdict about the name.
+  if (typeof navigator !== "undefined" && navigator.onLine === false) kind = "offline";
+
   const $ = (id) => document.getElementById(id);
   const el = (tag, cls, txt) => { const e = document.createElement(tag); if (cls) e.className = cls; if (txt != null) e.textContent = txt; return e; };
   const hostSpan = (h) => { const s = el("span", "host"); s.textContent = h || "(no host)"; return s; };
@@ -93,6 +113,25 @@
 
   // Kind → title, subtitle, body, actions.
   const configs = {
+    "offline": {
+      icon: "⌀", iconCls: "info",
+      title: "You appear to be offline",
+      sub:   "No network connection detected",
+      body:  (b) => {
+        b.append("This browser can't reach the network. Wi-Fi may be off, the cable may be unplugged, or a VPN / proxy may be dropping traffic. ");
+        b.append("Reconnect and press ");
+        const kbd = document.createElement("b"); kbd.textContent = "Retry"; b.append(kbd);
+        b.append(".");
+        if (host) {
+          b.append(document.createElement("br"));
+          b.append(document.createElement("br"));
+          b.append("Trying to open ");
+          b.append(hostSpan(host));
+          b.append(" — the address is kept so you can retry once you're back online.");
+        }
+      },
+      actions: ["retry", "home"],
+    },
     "name-not-registered": {
       icon: "?", iconCls: "warn",
       title: "That name isn't registered",
@@ -184,6 +223,29 @@
     b.addEventListener("click", def.fn);
     actionsBox.appendChild(b);
   }
+
+  // "Did you mean" — for BCNR-name failures, ask main for near-matches in
+  // the warm shared index (Levenshtein ≤ 2, same TLD). No network — the
+  // index is local, so this works offline too. Clicking a suggestion
+  // retries the load at that host, preserving the original path if any.
+  if ((kind === "name-not-registered" || kind === "name-unreachable") && host && window.errorpage?.bnsSimilar) {
+    window.errorpage.bnsSimilar(host).then((matches) => {
+      if (!Array.isArray(matches) || !matches.length) return;
+      const row = $("suggestRow");
+      let origPath = "/";
+      try { const u = new URL(url); origPath = u.pathname + u.search + u.hash; } catch {}
+      for (const name of matches) {
+        const a = el("a", null, name);
+        a.href = "#";
+        a.addEventListener("click", (ev) => {
+          ev.preventDefault();
+          window.errorpage.retry("https://" + name + origPath);
+        });
+        row.appendChild(a);
+      }
+      $("suggest").hidden = false;
+    }).catch(() => {});
+  }
 </script>
 </body>
 </html>

main.js

@@ -2303,6 +2303,46 @@ ipcMain.handle("error-register", (e, host) => {
   navigateTab(activeId, url);
   return true;
 });
+// "Did you mean" for the error page. Returns up to `limit` BCNR-registered
+// names within a small edit distance of `host`, same TLD only. Uses the
+// warm sharedIndex — no network call, no wait — so an offline user still
+// gets suggestions if the index warmed at least once. Ranks by ascending
+// distance, then alphabetical for a stable list.
+function levenshtein(a, b) {
+  const m = a.length, n = b.length;
+  if (Math.abs(m - n) > 3) return 4; // early-out, we only care about ≤2
+  const prev = new Array(n + 1); for (let j = 0; j <= n; j++) prev[j] = j;
+  const cur = new Array(n + 1);
+  for (let i = 1; i <= m; i++) {
+    cur[0] = i;
+    for (let j = 1; j <= n; j++) {
+      const cost = a.charCodeAt(i - 1) === b.charCodeAt(j - 1) ? 0 : 1;
+      cur[j] = Math.min(cur[j - 1] + 1, prev[j] + 1, prev[j - 1] + cost);
+    }
+    for (let j = 0; j <= n; j++) prev[j] = cur[j];
+  }
+  return prev[n];
+}
+ipcMain.handle("error-bns-similar", (e, host) => {
+  if (!isErrorPageSender(e.sender)) return [];
+  const h = String(host || "").trim().toLowerCase();
+  if (!h || !sharedIndex || typeof sharedIndex.keys !== "function") return [];
+  const tld = tldOf(h);
+  if (!tld) return [];
+  const cands = [];
+  const maxDist = 2;
+  for (const key of sharedIndex.keys()) {
+    if (typeof key !== "string") continue;
+    // Same TLD only — a typo like "games.x" → "game.x" or "gaeme.x" → "game.x".
+    if (!key.endsWith("." + tld)) continue;
+    if (key === h) continue;
+    const d = levenshtein(h, key);
+    if (d <= maxDist) cands.push({ name: key, dist: d });
+    if (cands.length > 200) break; // hard cap so a huge index doesn't stall the render
+  }
+  cands.sort((a, b) => (a.dist - b.dist) || a.name.localeCompare(b.name));
+  return cands.slice(0, 3).map((c) => c.name);
+});
 ipcMain.handle("error-open-external", (e, url) => {
   if (!isErrorPageSender(e.sender)) return false;
   // Allowlist Silent Mode domains only — no arbitrary external opens from