fix(nostr-client): restore subscriptions and availability on relay reconnect

When a relay reconnects after a disconnect, all active subscriptions
(including Lightning.Pub RPC listener) are now re-established on the
new relay instance. Previously subscriptions were lost permanently.

Also publishes availability broadcast immediately on reconnect instead
of waiting up to 5 minutes for the next heartbeat.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/nostr-client/src/client.ts

@@ -116,6 +116,9 @@ export class NostrClient {
         }
       }
 
+      // Re-establish all active subscriptions on the new relay connection
+      this.resubscribeOnRelay(connection)
+
       this.emitEvent('connect', { relay: url })
     } catch (error) {
       connection.state = 'error'
@@ -175,6 +178,38 @@ export class NostrClient {
     })
   }
 
+  /**
+   * Re-establish all active subscriptions on a reconnected relay.
+   * When a relay drops and reconnects, the old Relay instance is gone —
+   * subscriptions need to be recreated on the new instance.
+   */
+  private resubscribeOnRelay(connection: RelayConnection): void {
+    if (!connection.relay) return
+
+    for (const [id, sub] of this.subscriptions) {
+      try {
+        const relaySub = connection.relay.subscribe(sub.filters, {
+          onevent: (event: Event) => {
+            sub.options.onEvent(event)
+            this.emitEvent('event', { relay: connection.config.url, event })
+          },
+          oneose: () => {
+            sub.options.onEose?.()
+          },
+        })
+        // Append to the existing close chain so unsubscribe() cleans up both
+        const prevClose = sub.close
+        sub.close = () => {
+          prevClose()
+          relaySub.close()
+        }
+        console.log(`[Nostr] Restored subscription ${id} on ${connection.config.url}`)
+      } catch (e) {
+        console.warn(`[Nostr] Failed to restore subscription ${id} on ${connection.config.url}:`, e)
+      }
+    }
+  }
+
   /**
    * Schedule a reconnection attempt
    */