vpn: lease a credential from the key-issuer instead of expecting one in the catalogue

Found by driving the add-on in a real Theseus rather than reasoning
about it. turnOn() failed with "Silent Mode · 1 is not yet configured
(ready)" — resolveEndpoint required the catalogue entry to carry a
vless URL, but the gateway catalogue deliberately ships none, because a
vless URL is the credential and that endpoint is public. The add-on
predates the key-issuer and was never taught to ask for a lease.

It now POSTs to /api/vpn/session for any ready exit that has no URL of
its own, and caches the lease under its serverId until a minute before
expiry. Baked-in and subscription entries still use their own URL and
never hit the network.

bundled-addons/vpn/index.js

@@ -24,6 +24,7 @@ const { spawn } = require("node:child_process");
 const BINARY_MANIFEST_FILE = "binary-manifest.json";
 const SERVER_LIST_FILE = "server-list.json";
 const SERVER_LIST_URL = "https://navigate.st/api/vpn/servers";
+const SESSION_URL = "https://navigate.st/api/vpn/session";
 const CACHE_SUBDIR = "bin";
 const CONFIG_SUBDIR = "run";
 const DOWNLOAD_TIMEOUT_MS = 5 * 60_000;
@@ -422,6 +423,40 @@ module.exports = {
       return file;
     }
 
+    // Ask the key-issuer for a session credential on this exit. Leases are
+    // cached under their serverId and reused until they expire — the gateway
+    // returns the same lease for a repeat caller anyway, but not re-asking on
+    // every toggle keeps the round trip off the common path and means a brief
+    // gateway outage does not break an already-working exit.
+    async function leaseEndpoint(srv) {
+      const cacheKey = `__lease:${srv.id}`;
+      try {
+        const cached = await api.storage.get(cacheKey, null);
+        if (cached && cached.vless && cached.expiresAt > Date.now() + 60_000) return cached.vless;
+      } catch {}
+      const controller = new AbortController();
+      const t = setTimeout(() => controller.abort(), 20_000);
+      let r, body;
+      try {
+        r = await fetch(SESSION_URL, {
+          method: "POST",
+          headers: { "content-type": "application/json" },
+          body: JSON.stringify({ serverId: srv.id, tier: "free" }),
+          signal: controller.signal,
+        });
+        body = await r.text();
+      } catch (e) {
+        throw new Error(`could not reach the key issuer: ${e?.message || e}`);
+      } finally { clearTimeout(t); }
+      let j;
+      try { j = JSON.parse(body); }
+      catch { throw new Error(`key issuer returned non-JSON (${body.slice(0, 80)}…)`); }
+      if (!r.ok || !j.vless) throw new Error(j.error || `key issuer said HTTP ${r.status}`);
+      try { await api.storage.set(cacheKey, { vless: j.vless, expiresAt: j.expiresAt || 0 }); } catch {}
+      api.log(`leased a session on ${srv.id}${j.reused ? " (reused)" : ""}`);
+      return j.vless;
+    }
+
     // Resolve either a raw vless:// URL or a serverId lookup into the URL to
     // hand to sing-box. The panel usually sends { serverId } for a preset and
     // { vless } for a custom paste; either shape is accepted. A serverId of
@@ -438,10 +473,15 @@ module.exports = {
         }
         const hit = serverList.find((s) => s.id === serverId);
         if (!hit) throw new Error(`no server with id ${serverId} in the catalog`);
-        if (!hit.vless || hit.status === "coming-soon") {
-          throw new Error(`${hit.label || serverId} is not yet configured (${hit.status || "no vless URL"})`);
+        // A baked-in or subscription entry carries its own URL. A Silent Mode
+        // exit from the gateway catalogue deliberately does not: the catalogue
+        // is public, and a vless URL is the credential. For those we lease one
+        // from the key-issuer, which hands out a per-caller UUID.
+        if (hit.vless) return hit.vless;
+        if (hit.status && hit.status !== "ready") {
+          throw new Error(`${hit.label || serverId} is not available (${hit.status})`);
         }
-        return hit.vless;
+        return await leaseEndpoint(hit);
       }
       throw new Error("no endpoint — pass { vless } or { serverId }");
     }