feat(packaging): ship a node firewall profile for inbound WebRTC

The packages carried a profile for LAN casting and none for the node's own
peer traffic, on the reasoning that the node exposes only a loopback admin
API. That is true of its administration surface and false of its transport.

WebRTC binds an ephemeral UDP port per connection, so there is no fixed port
to open, and a connection succeeds only if one side can initiate. Browsers
publish their host candidate as an mDNS `<uuid>.local` name, which aioice
cannot resolve on any platform and discards — so the node can never call a
browser back, and the browser must call the node. A node that refuses
unsolicited inbound UDP is unreachable from every browser on its own LAN,
leaving reflexive candidates, which fail whenever both peers share one public
IP and the router will not hairpin.

Hit twice in one session on two different hosts: a firewalld zone narrowed to
mdns + 19550-19553/tcp, and a ufw host with default deny-incoming. Both
presented as "the app cannot connect", neither as a firewall message.

Passive like the cast profile: packaged, not activated. The guide says to
scope it to a LAN zone or source, including the libvirt case, where traffic
from a guest to its own hypervisor is not masqueraded and so must be scoped
to the guest subnet rather than the LAN.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DtfG7z6wHWj8RKHCvxQtY1

1 files changed, 30 insertions, 0 deletions

diff --git a/docs/PACKAGING-GUIDE.md b/docs/PACKAGING-GUIDE.md
index 5a5c388..56504d4 100644
--- a/docs/PACKAGING-GUIDE.md
+++ b/docs/PACKAGING-GUIDE.md
@@ -202,6 +202,36 @@ sudo firewall-cmd --reload
 sudo ufw allow "MeshBay Cast"
 ```
 
+### Peer connections (node)
+
+Opens inbound UDP 1024-65535. **Scope it to the LAN** — apply the firewalld
+service to the zone holding the LAN interface, and give the ufw rule a
+`from`. It does not belong in an internet-facing zone.
+
+```bash
+# Fedora (firewalld) — replace FedoraWorkstation with your LAN zone
+sudo firewall-cmd --permanent --zone=FedoraWorkstation --add-service=meshbay-node
+sudo firewall-cmd --reload
+
+# Ubuntu (ufw)
+sudo ufw allow from 192.168.1.0/24 app "MeshBay Node"
+
+# a libvirt guest reaching the node on its own hypervisor: scope to the guest
+# subnet, since traffic to the host's own address is not masqueraded
+sudo ufw allow in on virbr0 from 192.168.200.0/24 app "MeshBay Node"
+```
+
+**Why a node needs this.** WebRTC binds an ephemeral UDP port per connection,
+so there is no fixed port to open. A connection succeeds if *either* side can
+initiate. Browsers publish their host candidate as an mDNS `<uuid>.local`
+name, which `aioice` cannot resolve on any platform and discards — so the node
+can never call a browser back, and the browser must call the node. A node that
+refuses unsolicited inbound UDP is unreachable from every browser on its own
+LAN, and falls back to reflexive candidates, which fail whenever both peers
+share one public IP and the router will not hairpin.
+
+The node's administration surface is unaffected: loopback only, see below.
+
 The node's own administration surface is a loopback API (127.0.0.1 only,
 per-run token) reached by the CLI and the desktop client's Node page. It is
 never network-exposed and ships no firewall profile.