Add 'Login as Guest' — no extension or nsec needed

Generates a fresh random nostr keypair client-side and signs the NIP-98
login with it, same mechanism as the existing nsec path but nothing is
typed by a human and nothing is ever displayed/saved — the key exists in
page memory only long enough to sign the one login request (lib/guest.ts).

Visible and clearly labeled on the login screen (unlike the de-emphasized
'paste an nsec' option), with an explicit note that it's disposable: if
the session is lost there's no way to recover the same identity, since
nothing was saved for the player to do it with. Verified end-to-end
locally with a real generated key before deploying.

frontend/src/lib/guest.ts

@@ -0,0 +1,30 @@
+// Guest login: a freshly generated, throwaway nostr identity, signed
+// client-side — no NIP-07 extension needed, no nsec to paste. Same
+// never-persisted-key posture as lib/nsec.ts (the key exists in page memory
+// only long enough to sign this one login event), except here nothing was
+// ever typed by a human, so there's no "don't paste your real key" risk to
+// warn about — it's random and disposable by construction.
+//
+// Tradeoff worth knowing: since the key is never saved anywhere (not even
+// as an nsec the player could copy down), losing the session cookie means
+// losing this identity for good — a fresh "Login as Guest" click makes a
+// brand new one, it can't recover the old pubkey's claims.
+import { finalizeEvent, generateSecretKey } from 'nostr-tools/pure';
+
+/** Generates a random identity and returns a signed NIP-98 Authorization header for it. */
+export function buildGuestNip98Header(url: string, method: string): string {
+  const sk = generateSecretKey();
+  const event = finalizeEvent(
+    {
+      kind: 27235,
+      created_at: Math.floor(Date.now() / 1000),
+      content: '',
+      tags: [
+        ['u', url],
+        ['method', method],
+      ],
+    },
+    sk,
+  );
+  return `Nostr ${btoa(JSON.stringify(event))}`;
+}

frontend/src/stores/auth.ts

@@ -2,6 +2,7 @@ import { defineStore } from 'pinia';
 import { api, apiUrl, ApiError } from '../lib/api';
 import { buildNip98Header, hasNip07 } from '../lib/nip07';
 import { buildNip98HeaderWithNsec, isValidNsec } from '../lib/nsec';
+import { buildGuestNip98Header } from '../lib/guest';
 
 export type Team = 'orange' | 'green';
 
@@ -63,6 +64,23 @@ export const useAuthStore = defineStore('auth', {
       this.pubkey = res.pubkey;
       this.team = res.team;
     },
+    /**
+     * A freshly generated, throwaway identity — no extension, no key to
+     * paste. The key only exists in page memory for this one signing call;
+     * losing the session means losing this identity for good, since nothing
+     * is saved for the player to recover it with.
+     */
+    async loginAsGuest() {
+      const url = apiUrl('/api/auth/login');
+      const header = buildGuestNip98Header(url, 'POST');
+      const res = await api.post<{ pubkey: string; team: Team | null }>(
+        '/api/auth/login',
+        undefined,
+        { authorization: header },
+      );
+      this.pubkey = res.pubkey;
+      this.team = res.team;
+    },
     async logout() {
       await api.post('/api/auth/logout');
       this.pubkey = null;

frontend/src/views/LoginView.vue

@@ -21,6 +21,18 @@ async function handleLogin() {
   }
 }
 
+async function handleGuestLogin() {
+  error.value = null;
+  loggingIn.value = true;
+  try {
+    await auth.loginAsGuest();
+  } catch (err) {
+    error.value = err instanceof Error ? err.message : String(err);
+  } finally {
+    loggingIn.value = false;
+  }
+}
+
 async function handleNsecLogin() {
   error.value = null;
   loggingIn.value = true;
@@ -57,6 +69,18 @@ async function handleNsecLogin() {
       No NIP-07 extension detected — install Alby or nos2x, or open this app from the Archipelago dashboard.
     </p>
 
+    <button
+      class="rounded border border-cyan-neon/50 px-5 py-2 font-display uppercase tracking-wider text-cyan-neon/90 transition hover:border-cyan-neon hover:text-cyan-neon disabled:opacity-50"
+      :disabled="loggingIn"
+      @click="handleGuestLogin"
+    >
+      {{ loggingIn ? 'Authenticating…' : 'Login as Guest' }}
+    </button>
+    <p class="max-w-sm text-xs text-cyan-neon/60">
+      Jumps in with a fresh throwaway identity — no extension, nothing to install. It's disposable: if you lose this
+      session there's no way to get the same identity back, so don't rely on it for territory you care about keeping.
+    </p>
+
     <button class="text-xs text-cyan-neon/60 underline hover:text-magenta-neon" @click="showNsecForm = !showNsecForm">
       {{ showNsecForm ? 'Hide' : 'Or paste an nsec (unsafe)' }}
     </button>