fix: reuse RNS instance when already running; setup detects seed liveness

bridge.py / gossip.py:
- Use RNS.Reticulum.get_instance() to reuse the running singleton instead
  of raising OSError when cmd_seed instantiates both RadicleBridge and
  GossipRelay with the same config_path

cli.py (cmd_setup):
- Added TCP port check via seed_node._port_open() to report whether the
  seed radicle-node is currently listening; prints start command if not
- Adjusted final summary: distinguishes "all checks passed + running" from
  "all checks passed but not started"

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/radicle_reticulum/bridge.py

@@ -123,8 +123,9 @@ class RadicleBridge:
         self.rad_home = rad_home
         self.state_path = state_path
 
-        # Initialize Reticulum
-        self.reticulum = RNS.Reticulum(config_path)
+        # Initialize Reticulum (reuse running instance if already started)
+        existing = RNS.Reticulum.get_instance()
+        self.reticulum = existing if existing is not None else RNS.Reticulum(config_path)
 
         # Identity
         if identity is None:

src/radicle_reticulum/cli.py

@@ -676,8 +676,20 @@ def cmd_setup(args):
         )
 
     print()
-    if ok:
-        print("All checks passed. Start the bridge with:")
+    print("Seed process...")
+
+    seed_listening = seed_node._port_open()
+    check(
+        f"Seed radicle-node listening on port {seed_port}",
+        seed_listening,
+        f"radicle-rns seed --seed-home {seed_home} --seed-port {seed_port}",
+    )
+
+    print()
+    if ok and seed_listening:
+        print("All checks passed. Seed is running.")
+    elif ok:
+        print("All checks passed. Start the seed with:")
         print(f"  radicle-rns seed")
     else:
         print("Setup incomplete. Follow the instructions above, then run:")

src/radicle_reticulum/gossip.py

@@ -121,7 +121,8 @@ class GossipRelay:
         self.auto_discover = auto_discover
         self.rad_home = rad_home
 
-        self.reticulum = RNS.Reticulum(config_path)
+        existing = RNS.Reticulum.get_instance()
+        self.reticulum = existing if existing is not None else RNS.Reticulum(config_path)
 
         self.destination = RNS.Destination(
             identity.rns_identity,