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/handlers/api_test.go

@@ -1654,9 +1654,25 @@ func TestHistoryUnknownBefore(t *testing.T) {
 		)
 	}
 
+	// History holds only PRIVMSG, so the id of the JOIN to
+	// #here is not in it.
+	var joinID string
+
+	queued, _ := tserver.pollMessages(token, 0)
+	for _, msg := range queued {
+		if msg[commandKey] == joinCmd && msg[toKey] == "#here" {
+			joinID, _ = msg["id"].(string)
+		}
+	}
+
+	if joinID == "" {
+		t.Fatal("expected a JOIN to #here in the queue")
+	}
+
 	cases := []struct{ name, before string }{
 		{"made-up id", "no-such-message"},
 		{"id from another channel", elsewhere[0].ID},
+		{"id of a JOIN", joinID},
 	}
 
 	for _, tc := range cases {
@@ -1671,6 +1687,101 @@ func TestHistoryUnknownBefore(t *testing.T) {
 	}
 }
 
+// TestHistoryReusedNick checks that a user who takes a nick
+// released by QUIT does not get the DMs sent to its previous
+// holder.
+func TestHistoryReusedNick(t *testing.T) {
+	const victim = "victimV"
+
+	tserver := newTestServer(t)
+	senderToken := tserver.createSession("dmA")
+	victimToken := tserver.createSession(victim)
+	newcomerToken := tserver.createSession("newcomer")
+
+	tserver.sendCommand(senderToken, map[string]any{
+		commandKey: privmsgCmd,
+		toKey:      victim,
+		bodyKey:    []string{"for the first victimV only"},
+	})
+
+	_, msgs := tserver.getHistory(victimToken, victim, "", 10)
+	if len(msgs) != 1 {
+		t.Fatalf("expected 1 DM for %s, got %d", victim, len(msgs))
+	}
+
+	tserver.sendCommand(victimToken, map[string]any{
+		commandKey: irc.CmdQuit,
+	})
+
+	_, result := tserver.sendCommand(newcomerToken, map[string]any{
+		commandKey: irc.CmdNick,
+		bodyKey:    []string{victim},
+	})
+	if result[nickKey] != victim {
+		t.Fatalf("expected nick %s, got %v", victim, result)
+	}
+
+	status, msgs := tserver.getHistory(newcomerToken, victim, "", 10)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	if len(msgs) != 0 {
+		t.Fatalf("expected no history, got %v", msgs)
+	}
+}
+
+// TestHistoryRecreatedChannel checks that a channel created
+// again under the name of a deleted one starts with no
+// history, even when the old one had a key.
+func TestHistoryRecreatedChannel(t *testing.T) {
+	const channel = "#priv"
+
+	tserver := newTestServer(t)
+	ownerToken := tserver.createSession("roomR")
+	strangerToken := tserver.createSession("stranger")
+
+	tserver.sendCommand(ownerToken, map[string]any{
+		commandKey: joinCmd, toKey: channel,
+	})
+	tserver.sendCommand(ownerToken, map[string]any{
+		commandKey: irc.CmdMode,
+		toKey:      channel,
+		bodyKey:    []string{"+k", "topsecret"},
+	})
+	tserver.sendCommand(ownerToken, map[string]any{
+		commandKey: privmsgCmd,
+		toKey:      channel,
+		bodyKey:    []string{"members only"},
+	})
+
+	_, msgs := tserver.getHistory(ownerToken, channel, "", 10)
+	if len(msgs) != 1 {
+		t.Fatalf("expected 1 message, got %d", len(msgs))
+	}
+
+	// The last member leaving deletes the channel.
+	tserver.sendCommand(ownerToken, map[string]any{
+		commandKey: irc.CmdPart, toKey: channel,
+	})
+
+	_, result := tserver.sendCommand(strangerToken, map[string]any{
+		commandKey: joinCmd, toKey: channel,
+	})
+	if result[statusKey] != joinedStatus {
+		t.Fatalf("expected the join to succeed, got %v", result)
+	}
+
+	status, msgs := tserver.getHistory(strangerToken, channel, "", 10)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	if len(msgs) != 0 {
+		t.Fatalf("expected no history, got %v", msgs)
+	}
+}
+
 func TestChannelList(t *testing.T) {
 	tserver := newTestServer(t)
 	token := tserver.createSession("lister")