Bind history to the recipient session and channel, not the name (closes #148)

History was selected by msg_to, so whoever next held a released nick, or
created a deleted channel again under its old name, could read the
earlier holder's messages. Each message row now records the session a
DM or INVITE was sent to (to_session_id) and the channel a channel
message was sent to (to_channel_id), and GET /api/v1/history selects by
the one that applies, using its index. A session's DM history now also
follows it across nick changes. A DM or channel message whose recipient
is deleted before it is stored gets the unknown nick or channel error.

Model: opus-5-5

internal/service/service_test.go

@@ -164,7 +164,7 @@ func TestFanOut(t *testing.T) {
 	body, _ := json.Marshal([]string{"hello"}) //nolint:errchkjson
 
 	dbID, uuid, err := env.svc.FanOut(
-		ctx, irc.CmdPrivmsg, "alice", "#test",
+		ctx, irc.CmdPrivmsg, "alice", "#test", 0, 0,
 		nil, body, nil,
 		[]int64{sid1, sid2},
 	)
@@ -339,6 +339,78 @@ func TestBroadcastQuit(t *testing.T) {
 	}
 }
 
+// TestSendDirectMessageTargetQuits checks that a DM whose
+// target quits after its nick is looked up gets the same
+// error as a DM to an unknown nick. The trigger deletes the
+// target's session just before the DM is stored.
+func TestSendDirectMessageTargetQuits(t *testing.T) {
+	env := newTestEnv(t)
+	ctx := t.Context()
+
+	sid := createSession(ctx, t, env.db, "alice")
+	createSession(ctx, t, env.db, "bob")
+
+	_, err := env.db.GetDB().ExecContext(ctx,
+		`CREATE TRIGGER delete_recipient
+		 BEFORE INSERT ON messages
+		 BEGIN
+		   DELETE FROM sessions WHERE id = NEW.to_session_id;
+		 END`)
+	if err != nil {
+		t.Fatalf("create trigger: %v", err)
+	}
+
+	body, _ := json.Marshal([]string{"hi"}) //nolint:errchkjson
+
+	_, err = env.svc.SendDirectMessage(
+		ctx, sid, "alice", irc.CmdPrivmsg, "bob", body, nil,
+	)
+
+	var ircErr *service.IRCError
+	if !errors.As(err, &ircErr) || ircErr.Code != irc.ErrNoSuchNick {
+		t.Fatalf("want ERR_NOSUCHNICK, got %v", err)
+	}
+}
+
+// TestSendChannelMessageChannelDeleted checks that a channel
+// message whose channel is deleted after it is looked up gets
+// the same error as a message to an unknown channel. The
+// trigger deletes the channel just before the message is
+// stored.
+func TestSendChannelMessageChannelDeleted(t *testing.T) {
+	env := newTestEnv(t)
+	ctx := t.Context()
+
+	sid := createSession(ctx, t, env.db, "alice")
+
+	_, err := env.svc.JoinChannel(ctx, sid, "alice", "#gone", "")
+	if err != nil {
+		t.Fatalf("join alice: %v", err)
+	}
+
+	_, err = env.db.GetDB().ExecContext(ctx,
+		`CREATE TRIGGER delete_recipient
+		 BEFORE INSERT ON messages
+		 BEGIN
+		   DELETE FROM channels WHERE id = NEW.to_channel_id;
+		 END`)
+	if err != nil {
+		t.Fatalf("create trigger: %v", err)
+	}
+
+	body, _ := json.Marshal([]string{"hi"}) //nolint:errchkjson
+
+	_, _, err = env.svc.SendChannelMessage(
+		ctx, sid, "alice", irc.CmdPrivmsg, "#gone", body, nil,
+	)
+
+	var ircErr *service.IRCError
+	if !errors.As(err, &ircErr) ||
+		ircErr.Code != irc.ErrNoSuchChannel {
+		t.Fatalf("want ERR_NOSUCHCHANNEL, got %v", err)
+	}
+}
+
 func TestSendChannelMessage_Moderated(t *testing.T) {
 	env := newTestEnv(t)
 	ctx := t.Context()