The webhook adapter defaulted to host='0.0.0.0' — IPv4 only. On Fly.io
hosted agents the edge router (hermes-agent-router) reverse-proxies public
webhook traffic to <app>.internal:8644 over 6PN, Fly's private network,
which is IPv6-only (.internal resolves to an fdaa:… address). An IPv4-only
listener is unreachable there, so public webhook POSTs to
https://<agent>.agents.nousresearch.com/webhooks/<route> never landed on
the adapter — the router's dial was refused.
Fix: DEFAULT_HOST = None, which makes aiohttp/asyncio create_server bind
BOTH address families. '::' is NOT a valid substitute: on hosts where the
kernel sets bindv6only=1 (verified on Fly machines) it yields an IPv6-only
socket, breaking the IPv4 loopback /health check and the AF_INET
port-conflict probe in connect(). None binds per-family regardless of the
sysctl. An explicit empty-string/null host in config now also normalises to
None (dual-stack) rather than an invalid host=''. Users can still pin a
specific host via platforms.webhook.extra.host.
Validated live on a Fly staging agent: with this default and no config
override, the adapter binds both v4 and v6 (127.0.0.1:8644 and [::1]:8644
both answer), and a public signed webhook POST through the router returns
202 (valid sig) / 401 (bad sig) instead of the router's 502.
Tests: new TestDualStackBind asserts the None default, config resolution
(missing/empty→None, pinned preserved), and a real dual-stack bind opens
both AF_INET and AF_INET6 listeners. Red-proof: these fail on the old
'0.0.0.0' default.
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