feat: configurable STUN server fallbacks for WebRTC ICE

The WebRTC transport relied on a single Google STUN server — if it was
unreachable, ICE gathering waited the full 4s timeout. Now four public
servers are used by default (Google ×2, Cloudflare, Mozilla), configurable
via node.toml, the Node page UI, and the CLI (meshbay-node stun list|add|
remove|reset). Changes are hot-swapped on the live transport.

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

1 files changed, 15 insertions, 0 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/config.py b/packages/meshbay-node/src/meshbay_node/config.py
index 5d9282d..b94d03a 100644
--- a/packages/meshbay-node/src/meshbay_node/config.py
+++ b/packages/meshbay-node/src/meshbay_node/config.py
@@ -18,6 +18,13 @@ except ImportError:
 
 log = logging.getLogger(__name__)
 
+DEFAULT_STUN_SERVERS: list[str] = [
+    "stun:stun.l.google.com:19302",
+    "stun:stun1.l.google.com:19302",
+    "stun:stun.cloudflare.com:3478",
+    "stun:stun.services.mozilla.com:3478",
+]
+
 DEFAULT_CONFIG_PATH = Path.home() / ".config" / "meshbay" / "node.toml"
 
 EXAMPLE_CONFIG = """\
@@ -57,6 +64,10 @@ transcode_incompatible_video = true
 # gathering to specific interfaces (by OS adapter name).
 # ice_interfaces = ["wlp0s20f3", "eth0"]
 
+# STUN servers for WebRTC ICE candidate gathering (NAT traversal). By default
+# four public servers are used; set this to override.
+# stun_servers = ["stun:stun.l.google.com:19302", "stun:stun.cloudflare.com:3478"]
+
 # Browser and native clients reach this node over WebRTC DataChannel via hub
 # signaling — no inbound port to open. QUIC is the optional direct path.
 
@@ -145,6 +156,7 @@ class NodeConfig:
     # the gather for the full 5-second timeout — measured at 6 s total on a
     # machine with a Tailscale wt0 interface.
     ice_interfaces: list[str] = field(default_factory=list)  # include-list overrides auto
+    stun_servers: list[str] = field(default_factory=list)  # empty = DEFAULT_STUN_SERVERS
 
 
 @dataclass
@@ -305,6 +317,9 @@ def load_config(path: Path = DEFAULT_CONFIG_PATH) -> Config:
         ice_if = nd.get("ice_interfaces")
         if isinstance(ice_if, list):
             cfg.node.ice_interfaces = [str(s) for s in ice_if]
+        stun = nd.get("stun_servers")
+        if isinstance(stun, list):
+            cfg.node.stun_servers = [str(s) for s in stun]
 
         # Multi-group: [[groups]] array
         if "groups" in raw: