Index, probe, and announce LNURL mints in the API.

Wire discovery and probing for LNURL mints, add rate-limited POST /api/index
for user submissions, and optionally announce confirmed state to relays.

Co-authored-by: Cursor <cursoragent@cursor.com>

api/src/config.ts

@@ -119,4 +119,39 @@ export const config = {
   userAgent: 'cashumints.space-indexer/1.0',
 } as const;
 
+/**
+ * Publishing `kind:38174` announcements, which is **off unless two switches are set**.
+ *
+ * One switch would be enough to make it work and is not enough to make it safe. This
+ * writes signed events to public relays, permanently and under this site's name, so
+ * turning it on has to be a thing somebody did on purpose rather than a thing that
+ * happened because a key was left in an env file from a test run:
+ *
+ *   ANNOUNCE_LNURL=true      the intent
+ *   ANNOUNCE_KEY=nsec1…      the identity it will be signed with
+ *   ANNOUNCE_RELAYS=wss://…  where, explicitly — there is deliberately no default
+ *
+ * The missing default on ANNOUNCE_RELAYS is the important one. Falling back to the
+ * site's read pool would mean the difference between a CI run against a local test relay
+ * and a permanent write to five public ones was a single unset variable.
+ *
+ * Returns null — never throws — when any of the three is missing, because a
+ * misconfigured publisher must not stop an indexer that still has a directory to serve.
+ * See the README section "Publishing LNURL mint announcements".
+ */
+export function announceConfig(
+  env: NodeJS.ProcessEnv = process.env,
+): { secretKey: string; relays: string[] } | null {
+  if (env['ANNOUNCE_LNURL']?.trim().toLowerCase() !== 'true') return null;
+
+  const secretKey = env['ANNOUNCE_KEY']?.trim() ?? '';
+  const relays = (env['ANNOUNCE_RELAYS'] ?? '')
+    .split(',')
+    .map((relay) => relay.trim())
+    .filter((relay) => relay.startsWith('ws://') || relay.startsWith('wss://'));
+
+  if (!secretKey || relays.length === 0) return null;
+  return { secretKey, relays };
+}
+
 export const startedAt = Math.floor(Date.now() / 1000);