Initial commit

Adds a happyDomain checker that probes STUN/TURN servers end-to-end:
DNS/SRV discovery, UDP/TCP/TLS/DTLS dial, STUN binding + reflexive-addr
sanity, open-relay detection, authenticated TURN Allocate (long-term
creds or REST-API HMAC), public-relay check, CreatePermission + Send
round-trip through the relay, and optional ChannelBind.

Failing sub-tests carry a remediation string (`Fix`) that the HTML
report surfaces as a yellow headline callout and inline next to each
row. Mapping covers the most common coturn misconfigurations
(external-ip, relay-ip, lt-cred-mech, min-port/max-port, cert issues,
401 nonce drift, 441/442/486/508 allocation errors).

Implements sdk.EndpointDiscoverer (checker/discovery.go): every
stuns:/turns:/DTLS endpoint observed during Collect is published as a
DiscoveredEndpoint{Type: "tls"|"dtls"} so a downstream TLS checker can
verify certificates without re-parsing the observation.

Backed by pion/stun/v3 + pion/turn/v4 + pion/dtls/v3; SDK pinned to a
local replace until the EndpointDiscoverer interface ships in a tagged
release.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

checker/discovery.go

@@ -0,0 +1,47 @@
+package checker
+
+import (
+	"fmt"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// DiscoverEndpoints implements sdk.EndpointDiscoverer. It publishes every
+// TLS/DTLS endpoint seen during collection so a downstream TLS checker can
+// verify certificates without re-parsing the observation.
+//
+// stuns:/turns: speak TLS immediately after the TCP handshake (no STARTTLS),
+// so we emit Type="tls". DTLS endpoints are published as Type="dtls" — an
+// open-string convention, consumed by DTLS-aware probes.
+func (p *stunTurnProvider) DiscoverEndpoints(data any) ([]sdk.DiscoveredEndpoint, error) {
+	d, ok := data.(*StunTurnData)
+	if !ok {
+		return nil, fmt.Errorf("unexpected data type %T", data)
+	}
+	seen := make(map[string]struct{})
+	var out []sdk.DiscoveredEndpoint
+	for _, ep := range d.Endpoints {
+		if !ep.Endpoint.Secure {
+			continue
+		}
+		epType := "tls"
+		if ep.Endpoint.Transport == TransportDTLS {
+			epType = "dtls"
+		}
+		key := fmt.Sprintf("%s|%s|%d", epType, ep.Endpoint.Host, ep.Endpoint.Port)
+		if _, dup := seen[key]; dup {
+			continue
+		}
+		seen[key] = struct{}{}
+		out = append(out, sdk.DiscoveredEndpoint{
+			Type: epType,
+			Host: ep.Endpoint.Host,
+			Port: ep.Endpoint.Port,
+			Meta: map[string]any{
+				"source": "stun-turn",
+				"uri":    ep.Endpoint.URI,
+			},
+		})
+	}
+	return out, nil
+}