seed default channel(s) on boot

fresh relay seeds configured open channels (RELAY_DEFAULT_CHANNELS,
default general) so a client always has a room. relay-signed 9007
through the normal pipeline; idempotent; never reopens a closed group.

also adds mission/roadmap and separation rationale to the readme.

cmd/nostermd/relay.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"log"
 	"net/http"
 
 	"fiatjaf.com/nostr"
@@ -24,18 +25,23 @@ type relayConfig struct {
 	description string
 	contact     string
 	motd        string
-	fedCfg      federation.Config
+	// defaultChannels are group ids seeded as open channels on boot so a fresh
+	// relay is never empty — a client always has at least one room to join.
+	defaultChannels []string
+	fedCfg          federation.Config
 }
 
 // relayApp is a fully-wired relay: the khatru relay, its HTTP handler, the group
 // state authority, and (when configured) the federator. main starts/stops these;
 // tests assert against them.
 type relayApp struct {
-	relay     *khatru.Relay
-	handler   http.Handler
-	groups    *group.State
-	federator *federation.Federator
-	pubKey    nostr.PubKey
+	relay           *khatru.Relay
+	handler         http.Handler
+	groups          *group.State
+	federator       *federation.Federator
+	pubKey          nostr.PubKey
+	secretKey       nostr.SecretKey
+	defaultChannels []string
 }
 
 // buildRelay assembles the relay from its internal packages and wires khatru's
@@ -146,11 +152,42 @@ func buildRelay(cfg relayConfig) *relayApp {
 	})
 
 	return &relayApp{
-		relay:     relay,
-		handler:   mux,
-		groups:    groups,
-		federator: fed,
-		pubKey:    pk,
+		relay:           relay,
+		handler:         mux,
+		groups:          groups,
+		federator:       fed,
+		pubKey:          pk,
+		secretKey:       cfg.secretKey,
+		defaultChannels: cfg.defaultChannels,
+	}
+}
+
+// SeedDefaultChannels creates any configured default channel that doesn't
+// already exist, so a fresh relay always has at least one room to join. Each
+// missing channel is created by the relay identity via a signed kind-9007
+// create-group event pushed through the normal add pipeline (OnEvent → store →
+// OnEventSaved), so it persists, replays on restart, and publishes its 39000/
+// 39001/39002 lists exactly like a client-created group. Existing channels are
+// left untouched. Call after Rebuild so it only seeds what's genuinely missing.
+func (app *relayApp) SeedDefaultChannels(ctx context.Context) {
+	for _, id := range app.defaultChannels {
+		if id == "" || app.groups.Has(id) {
+			continue
+		}
+		evt := nostr.Event{
+			Kind:      nostr.KindSimpleGroupCreateGroup,
+			CreatedAt: nostr.Now(),
+			Tags:      nostr.Tags{{"h", id}},
+		}
+		if err := evt.Sign(app.secretKey); err != nil {
+			log.Printf("could not sign default-channel create for %q: %v", id, err)
+			continue
+		}
+		if _, err := app.relay.AddEvent(ctx, evt); err != nil {
+			log.Printf("could not seed default channel %q: %v", id, err)
+			continue
+		}
+		log.Printf("seeded default channel %q", id)
 	}
 }