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.go

@@ -311,7 +311,7 @@ func (s *Service) SendWallops(
 	}
 
 	_, _, err = s.FanOut(
-		ctx, irc.CmdWallops, nick, "*",
+		ctx, irc.CmdWallops, nick, "*", 0, 0,
 		nil, body, nil, recipients,
 	)
 	if err != nil {
@@ -344,15 +344,19 @@ type DirectMsgResult struct {
 }
 
 // FanOut inserts a message and enqueues it to all given
-// session IDs, notifying each via the broker.
+// session IDs, notifying each via the broker. toSessionID
+// and toChannelID are the recipient InsertMessage records
+// for history, 0 when there is none.
 func (s *Service) FanOut(
 	ctx context.Context,
 	command, from, to string,
+	toSessionID, toChannelID int64,
 	params, body, meta json.RawMessage,
 	sessionIDs []int64,
 ) (int64, string, error) {
 	dbID, msgUUID, err := s.db.InsertMessage(
-		ctx, command, from, to, params, body, meta,
+		ctx, command, from, to,
+		toSessionID, toChannelID, params, body, meta,
 	)
 	if err != nil {
 		return 0, "", fmt.Errorf("insert message: %w", err)
@@ -396,13 +400,13 @@ func (s *Service) SendChannelMessage(
 	nick, command, channel string,
 	body, meta json.RawMessage,
 ) (int64, string, error) {
+	noSuchChannel := &IRCError{
+		irc.ErrNoSuchChannel, []string{channel}, msgNoSuchChannel,
+	}
+
 	chID, err := s.db.GetChannelByName(ctx, channel)
 	if err != nil {
-		return 0, "", &IRCError{
-			irc.ErrNoSuchChannel,
-			[]string{channel},
-			msgNoSuchChannel,
-		}
+		return 0, "", noSuchChannel
 	}
 
 	if command == irc.CmdPrivmsg {
@@ -459,9 +463,14 @@ func (s *Service) SendChannelMessage(
 	recipients := excludeSession(memberIDs, sessionID)
 
 	dbID, uuid, fanErr := s.FanOut(
-		ctx, command, nick, channel,
+		ctx, command, nick, channel, 0, chID,
 		nil, body, meta, recipients,
 	)
+	// The channel was deleted after the lookup above.
+	if db.IsForeignKeyConstraintError(fanErr) {
+		return 0, "", noSuchChannel
+	}
+
 	if fanErr != nil {
 		return 0, "", fanErr
 	}
@@ -478,13 +487,13 @@ func (s *Service) SendDirectMessage(
 	nick, command, target string,
 	body, meta json.RawMessage,
 ) (*DirectMsgResult, error) {
+	noSuchNick := &IRCError{
+		irc.ErrNoSuchNick, []string{target}, "No such nick",
+	}
+
 	targetSID, err := s.db.GetSessionByNick(ctx, target)
 	if err != nil {
-		return nil, &IRCError{
-			irc.ErrNoSuchNick,
-			[]string{target},
-			"No such nick",
-		}
+		return nil, noSuchNick
 	}
 
 	away, _ := s.db.GetAway(ctx, targetSID)
@@ -495,9 +504,14 @@ func (s *Service) SendDirectMessage(
 	}
 
 	_, uuid, fanErr := s.FanOut(
-		ctx, command, nick, target,
+		ctx, command, nick, target, targetSID, 0,
 		nil, body, meta, recipients,
 	)
+	// The target's session was deleted after the lookup above.
+	if db.IsForeignKeyConstraintError(fanErr) {
+		return nil, noSuchNick
+	}
+
 	if fanErr != nil {
 		return nil, fanErr
 	}
@@ -561,7 +575,7 @@ func (s *Service) JoinChannel(
 	body, _ := json.Marshal([]string{channel}) //nolint:errchkjson
 
 	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
-		ctx, irc.CmdJoin, nick, channel,
+		ctx, irc.CmdJoin, nick, channel, 0, chID,
 		nil, body, nil, memberIDs,
 	)
 
@@ -604,7 +618,7 @@ func (s *Service) PartChannel(
 	body, _ := json.Marshal([]string{reason}) //nolint:errchkjson
 
 	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
-		ctx, irc.CmdPart, nick, channel,
+		ctx, irc.CmdPart, nick, channel, 0, chID,
 		nil, body, nil, recipients,
 	)
 
@@ -666,7 +680,7 @@ func (s *Service) SetTopic(
 	body, _ := json.Marshal([]string{topic}) //nolint:errchkjson
 
 	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
-		ctx, irc.CmdTopic, nick, channel,
+		ctx, irc.CmdTopic, nick, channel, 0, chID,
 		nil, body, nil, memberIDs,
 	)
 
@@ -730,7 +744,7 @@ func (s *Service) KickUser(
 	)
 
 	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
-		ctx, irc.CmdKick, nick, channel,
+		ctx, irc.CmdKick, nick, channel, 0, chID,
 		params, body, nil, memberIDs,
 	)
 
@@ -886,7 +900,7 @@ func (s *Service) BroadcastQuit(
 		body, _ := json.Marshal([]string{reason}) //nolint:errchkjson
 
 		_, _, _ = s.FanOut(
-			ctx, irc.CmdQuit, nick, "",
+			ctx, irc.CmdQuit, nick, "", 0, 0,
 			nil, body, nil, recipients,
 		)
 	}
@@ -1074,7 +1088,7 @@ func (s *Service) BroadcastMode(
 	body, _ := json.Marshal([]string{modeText}) //nolint:errchkjson
 
 	_, _, _ = s.FanOut( //nolint:dogsled // fire-and-forget broadcast
-		ctx, irc.CmdMode, nick, channel,
+		ctx, irc.CmdMode, nick, channel, 0, chID,
 		nil, body, nil, memberIDs,
 	)
 }
@@ -1351,7 +1365,7 @@ func (s *Service) broadcastNickChange(
 	notified := make(map[int64]bool)
 
 	dbID, _, insErr := s.db.InsertMessage(
-		ctx, irc.CmdNick, oldNick, "",
+		ctx, irc.CmdNick, oldNick, "", 0, 0,
 		nil, body, nil,
 	)
 	if insErr != nil {