Bring README.md in line with the modes and the schema (closes #119)

The MODE section described a query-only command. It now covers channel
and user mode queries and changes on the HTTP API and the IRC listener,
the letters each accepts, what is broadcast, and the error numerics.
The schema section now lists every table and column in
001_initial.sql.

Every other statement this change touches was checked against the code:
polled numerics carry their name in command and their number in code;
command errors are numerics with HTTP 200; the broker is keyed by
session; WAL is never on; a hostname falls back to the IP and is
public; and the IRC listener handles modes, NOTICE, INVITE, +s and +H
more narrowly, with gaps in its bridge to the HTTP API.

Model: opus-5-5

internal/db/queries.go

@@ -204,21 +204,42 @@ func (database *Database) GetSessionByToken(
 		)
 	}
 
+	_ = database.UpdateLastSeen(ctx, sessionID, clientID)
+
+	return sessionID, clientID, nick, nil
+}
+
+// UpdateLastSeen sets last_seen to now on a session and on
+// one of its clients, so that the idle cleanup keeps them.
+func (database *Database) UpdateLastSeen(
+	ctx context.Context,
+	sessionID, clientID int64,
+) error {
 	now := time.Now()
 
-	_, _ = database.conn.ExecContext(
+	_, err := database.conn.ExecContext(
 		ctx,
 		"UPDATE sessions SET last_seen = ? WHERE id = ?",
 		now, sessionID,
 	)
+	if err != nil {
+		return fmt.Errorf(
+			"update session last_seen: %w", err,
+		)
+	}
 
-	_, _ = database.conn.ExecContext(
+	_, err = database.conn.ExecContext(
 		ctx,
 		"UPDATE clients SET last_seen = ? WHERE id = ?",
 		now, clientID,
 	)
+	if err != nil {
+		return fmt.Errorf(
+			"update client last_seen: %w", err,
+		)
+	}
 
-	return sessionID, clientID, nick, nil
+	return nil
 }
 
 // GetSessionByNick returns session id for a given nick.

internal/ircserver/conn.go

@@ -368,6 +368,17 @@ func (c *Conn) handleMessage(
 		return
 	}
 
+	// Every command is activity, so the idle cleanup must not
+	// remove this user.
+	err := c.database.UpdateLastSeen(
+		ctx, c.sessionID, c.clientID,
+	)
+	if err != nil {
+		c.log.Error(
+			"failed to update last_seen", "error", err,
+		)
+	}
+
 	handler, ok := c.commands[msg.Command]
 	if !ok {
 		c.sendNumeric(

internal/ircserver/server_test.go

@@ -369,6 +369,39 @@ func TestPingPong(t *testing.T) {
 	assertContains(t, lines, "PONG", "PONG response")
 }
 
+// TestIdleCleanupKeepsActiveUser checks that a user who
+// sends commands is kept by the idle cleanup, and a user who
+// sends nothing is not.
+func TestIdleCleanupKeepsActiveUser(t *testing.T) {
+	t.Parallel()
+
+	const idleTimeout = 500 * time.Millisecond
+
+	env := newTestEnv(t)
+
+	active := env.dial(t)
+	active.register("active")
+
+	idle := env.dial(t)
+	idle.register("idle")
+
+	time.Sleep(idleTimeout)
+	active.sendAndExpect("PING :still here", "PONG")
+
+	// The idle cleanup in internal/handlers removes exactly
+	// the users this returns.
+	stale, err := env.database.GetStaleOrphanSessions(
+		t.Context(), time.Now().Add(-idleTimeout),
+	)
+	if err != nil {
+		t.Fatalf("get stale sessions: %v", err)
+	}
+
+	if len(stale) != 1 || stale[0].Nick != "idle" {
+		t.Errorf("cleanup removes %v, want only idle", stale)
+	}
+}
+
 func TestJoinChannel(t *testing.T) {
 	t.Parallel()