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_test.go

@@ -192,3 +192,51 @@ func TestMultiUserAdminOverWebsocket(t *testing.T) {
 		t.Fatal("admin did not receive the admitted member's message")
 	}
 }
+
+// SeedDefaultChannels creates configured channels that don't exist yet, signed
+// by the relay, and is idempotent: seeding an already-present channel is a
+// no-op. A seeded open channel accepts chat without an explicit create.
+func TestSeedDefaultChannels(t *testing.T) {
+	store := &slicestore.SliceStore{}
+	if err := store.Init(); err != nil {
+		t.Fatalf("store init: %v", err)
+	}
+	app := buildRelay(relayConfig{
+		secretKey:       nostr.Generate(),
+		store:           store,
+		name:            "test-relay",
+		defaultChannels: []string{"general", "general", ""}, // dupes/blanks ignored
+	})
+
+	ctx := context.Background()
+	app.SeedDefaultChannels(ctx)
+	if !app.groups.Has("general") {
+		t.Fatal("expected default channel 'general' to be seeded")
+	}
+	// The seed event is signed by the relay identity.
+	if !app.groups.IsAdmin("general", app.pubKey) {
+		t.Fatal("expected the relay to be admin of the seeded channel")
+	}
+
+	// Idempotent: a second seed doesn't error or duplicate.
+	app.SeedDefaultChannels(ctx)
+
+	// Seeding never clobbers an existing channel: pre-create one closed, then a
+	// seed of the same id must leave it closed.
+	closed := nostr.Event{Kind: nostr.KindSimpleGroupCreateGroup, CreatedAt: nostr.Now(), Tags: nostr.Tags{{"h", "ops"}, {"closed"}}}
+	mustSign(t, app.secretKey, &closed)
+	if _, err := app.relay.AddEvent(ctx, closed); err != nil {
+		t.Fatalf("pre-create closed group: %v", err)
+	}
+	app.defaultChannels = []string{"ops"}
+	app.SeedDefaultChannels(ctx)
+	// A non-member posting to the still-closed 'ops' must be rejected.
+	stranger := nostr.Generate()
+	if reject, _ := app.groups.Evaluate(func() nostr.Event {
+		e := nostr.Event{Kind: nostr.KindSimpleGroupChatMessage, CreatedAt: nostr.Now(), Tags: nostr.Tags{{"h", "ops"}}}
+		mustSign(t, stranger, &e)
+		return e
+	}()); !reject {
+		t.Fatal("seed must not reopen a pre-existing closed channel")
+	}
+}