Extract MessageLine, Player pack ops, and Level list management

Refactor step 6. MessageLine (was MsgLine) owns the msg/addmsg/endmsg
machinery, wired to its screen, pre---More-- redraw, and input via
attach(); RogueGame keeps one-line msg/addmsgf/endmsg shorthands so
the ~400 call sites are unchanged. Player gains nextPackChar and
removeFromPack (the state half of pack.c leave_pack); leavePack keeps
only the LastPick repeat-command tracking. Level gains ObjectAt
(misc.c find_obj) and AddObject/RemoveObject/AddMonster/RemoveMonster,
replacing direct attach/detach calls on the level lists. Inventory and
pickup UI flows stay on RogueGame: display and orchestration, not
state surgery. Behavior and RNG order unchanged; suite green.

game/io.go

@@ -10,9 +10,11 @@ import (
 // maxMsg is io.c MAXMSG: how much message fits before --More--.
 const maxMsg = NumCols - len("--More--") - 1
 
-// MsgLine is the io.c message machinery: the static msgbuf/newpos pair plus
-// the related globals (mpos, huh, and the message-behavior flags).
-type MsgLine struct {
+// MessageLine is the io.c message machinery: the static msgbuf/newpos
+// pair plus the related globals (mpos, huh, and the message-behavior
+// flags). It owns the top line of the screen; attach wires in the
+// display and input it needs.
+type MessageLine struct {
 	buf      strings.Builder // msgbuf
 	newpos   int
 	Mpos     int    // where cursor is on top line
@@ -20,49 +22,52 @@ type MsgLine struct {
 	SaveMsg  bool   // remember last msg
 	LowerMsg bool   // messages should start w/lower case
 	MsgEsc   bool   // check for ESC from msg's --More--
+
+	scr      *Screen           // the top line lives on scr.Std
+	look     func(wakeup bool) // redraw before a --More-- (misc.c look)
+	readChar func() byte       // input for --More-- prompts
 }
 
 // Msg displays a message at the top of the screen (io.c msg). It returns
-// Escape if the player escaped out of a --More--, ^Escape otherwise (the C
-// convention: callers compare against ESCAPE).
-func (g *RogueGame) msg(format string, a ...any) int {
+// Escape if the player escaped out of a --More--, ^Escape otherwise (the
+// C convention: callers compare against ESCAPE).
+func (m *MessageLine) Msg(format string, a ...any) int {
 	// if the string is "", just clear the line
 	if format == "" {
-		g.move(0, 0)
-		g.clrtoeol()
-		g.Msgs.Mpos = 0
+		m.scr.Std.Move(0, 0)
+		m.scr.Std.Clrtoeol()
+		m.Mpos = 0
 
 		return ^Escape
 	}
 	// otherwise add to the message and flush it out
-	g.doaddf(format, a...)
+	m.doaddf(format, a...)
 
-	return g.endmsg()
+	return m.End()
 }
 
-// addmsgf adds things to the current message (io.c addmsg).
-func (g *RogueGame) addmsgf(format string, a ...any) {
-	g.doaddf(format, a...)
+// Addf adds things to the current message (io.c addmsg).
+func (m *MessageLine) Addf(format string, a ...any) {
+	m.doaddf(format, a...)
 }
 
-// endmsg displays a new msg, giving the player a chance to see the previous
+// End displays a new msg, giving the player a chance to see the previous
 // one if it is up there with the --More-- (io.c endmsg).
-func (g *RogueGame) endmsg() int {
-	m := &g.Msgs
+func (m *MessageLine) End() int {
 	if m.SaveMsg {
 		m.Huh = m.buf.String()
 	}
 
 	if m.Mpos != 0 {
-		g.look(false)
-		g.mvaddstr(0, m.Mpos, "--More--")
-		g.refresh()
+		m.look(false)
+		m.scr.Std.MvAddStr(0, m.Mpos, "--More--")
+		m.scr.Refresh()
 
 		if !m.MsgEsc {
-			g.waitFor(' ')
+			m.waitForSpace()
 		} else {
 			for {
-				ch := g.readchar()
+				ch := m.readChar()
 				if ch == ' ' {
 					break
 				}
@@ -85,30 +90,60 @@ func (g *RogueGame) endmsg() int {
 		out = string(toUpper(out[0])) + out[1:]
 	}
 
-	g.mvaddstr(0, 0, out)
-	g.clrtoeol()
+	m.scr.Std.MvAddStr(0, 0, out)
+	m.scr.Std.Clrtoeol()
 
 	m.Mpos = m.newpos
 	m.newpos = 0
 	m.buf.Reset()
-	g.refresh()
+	m.scr.Refresh()
 
 	return ^Escape
 }
 
-// doaddf performs an add onto the message buffer (io.c doadd).
-func (g *RogueGame) doaddf(format string, a ...any) {
-	m := &g.Msgs
+// attach wires the message line to its display and input; NewGame and
+// Restore call it once the screen and game exist.
+func (m *MessageLine) attach(scr *Screen, look func(bool), readChar func() byte) {
+	m.scr = scr
+	m.look = look
+	m.readChar = readChar
+}
 
+// waitForSpace absorbs input until the player types a space: the
+// --More-- acknowledgement (io.c wait_for).
+func (m *MessageLine) waitForSpace() {
+	for {
+		if m.readChar() == ' ' {
+			return
+		}
+	}
+}
+
+// doaddf performs an add onto the message buffer (io.c doadd).
+func (m *MessageLine) doaddf(format string, a ...any) {
 	s := fmt.Sprintf(format, a...)
 	if len(s)+m.newpos >= maxMsg {
-		g.endmsg()
+		m.End()
 	}
 
 	m.buf.WriteString(s)
 	m.newpos = m.buf.Len()
 }
 
+// msg, addmsgf, and endmsg are the game-side shorthands for the message
+// line; the machinery lives on MessageLine.
+func (g *RogueGame) msg(format string, a ...any) int {
+	return g.Msgs.Msg(format, a...)
+}
+
+func (g *RogueGame) addmsgf(format string, a ...any) {
+	g.Msgs.Addf(format, a...)
+}
+
+func (g *RogueGame) endmsg() {
+	g.Msgs.End()
+}
+
 // stepOk returns true if it is ok to step on ch (io.c step_ok).
 func stepOk(ch byte) bool {
 	switch ch {