diff --git a/cardsim/errors.go b/cardsim/errors.go
index 15fe45e..90ffdfb 100644
--- a/cardsim/errors.go
+++ b/cardsim/errors.go
@@ -52,6 +52,12 @@ func Warningf(f string, args ...any) *Warning {
 	return &Warning{fmt.Errorf(f, args...)}
 }
 
+// IsSeriousError returns whether e is a non-warning error. If e is nil, this
+// returns false.
+func IsSeriousError(e error) bool {
+	return !errors.Is(e, AnyWarning)
+}
+
 // A Failure is an error that is definitely not a Warning. If a Warning is
 // wrapped in a Failure, it stops being a Warning.
 type Failure struct {
@@ -144,8 +150,11 @@ func (f Failure) As(target any) bool {
 //   - Otherwise, it returns an error that combines all the errors it collected.
 //     The aggregated error is a Warning if and only if all collected errors
 //     were also warnings.
+//
+// An ErrorCollector's Errs should not be written by anything other than Add,
+// or HasFailure may get out of sync.
 type ErrorCollector struct {
-	errs       []error
+	Errs       []error
 	hasFailure bool
 }
 
@@ -157,12 +166,12 @@ func (ec *ErrorCollector) Add(e error) {
 	if !errors.Is(e, AnyWarning) {
 		ec.hasFailure = true
 	}
-	ec.errs = append(ec.errs, e)
+	ec.Errs = append(ec.Errs, e)
 }
 
 // IsEmpty reports whether ec has zero accumulated errors/warnings.
 func (ec *ErrorCollector) IsEmpty() bool {
-	return len(ec.errs) == 0
+	return len(ec.Errs) == 0
 }
 
 // HasFailure reports whether ec has at least one non-warning error.
@@ -181,16 +190,16 @@ func (ec *ErrorCollector) HasFailure() bool {
 // errors.Is does not erroneously represent a failure as a warning because it
 // contains a warning as a subcomponent.
 func (ec *ErrorCollector) Emit() error {
-	if len(ec.errs) == 0 {
+	if len(ec.Errs) == 0 {
 		return nil
 	}
-	if len(ec.errs) == 1 {
-		return ec.errs[0]
+	if len(ec.Errs) == 1 {
+		return ec.Errs[0]
 	}
 	if ec.HasFailure() {
-		return aggregateFailure(ec.errs)
+		return aggregateFailure(ec.Errs)
 	}
-	return &aggregateError{ec.errs} // all these are recognizable warnings
+	return &aggregateError{ec.Errs} // all these are recognizable warnings
 }
 
 // An aggregateError is a collection of errors that is itself an error.
diff --git a/cardsim/messages.go b/cardsim/messages.go
index b370696..acb0a6a 100644
--- a/cardsim/messages.go
+++ b/cardsim/messages.go
@@ -25,3 +25,34 @@ func MsgStr(s string) Message {
 func Msgf(f string, args ...any) Message {
 	return stringMessage(fmt.Sprintf(f, args...))
 }
+
+// A SpecialMessage is a specific, uniquely identifiable message.
+type SpecialMessage struct {
+	msg Message
+}
+
+// String implements Message.
+func (s *SpecialMessage) String() string {
+	if s == nil {
+		return ""
+	}
+	return s.msg.String()
+}
+
+// Messages that various display surfaces or other components may have a special interpretation of
+// and identify specifically. These are largely sentinel values. Nil is a paragraph break.
+var (
+	SectionBreak = &SpecialMessage{MsgStr("      --------------------------------------------------------------------      ")}
+	ChapterBreak = &SpecialMessage{MsgStr("      ====================================================================      ")}
+)
+
+// IsSpecialMessage returns whether a provided Message is a specific SpecialMessage.
+func IsSpecialMessage(m Message, s *SpecialMessage) bool {
+	if m == nil {
+		return s == nil
+	}
+	if s2, ok := m.(*SpecialMessage); ok {
+		return s == s2
+	}
+	return false
+}
diff --git a/cardsim/player.go b/cardsim/player.go
index 1f0da89..79a3a20 100644
--- a/cardsim/player.go
+++ b/cardsim/player.go
@@ -1,6 +1,15 @@
 package cardsim
 
-import "math/rand"
+import (
+	"errors"
+	"math/rand"
+)
+
+var (
+	ErrUncooperativeCards = errors.New("a milion cards refused to join the hand")
+
+	WarningStalemate = errors.New("no actions can be taken")
+)
 
 // Player stores all gameplay state for one player at a specific point in time.
 // Game-specific data is stored in Stats.
@@ -138,3 +147,111 @@ const (
 func (g GameState) Over() bool {
 	return g == GameLost || g == GameWon || g == GameCrashed || g == GameStalled
 }
+
+// ChapterBreak apends a chapter break to p.TemporaryMessages, unless it is
+// empty or the most recent non-nil message is already a chapter break.
+func (p *Player[C]) ChapterBreak() {
+	for i := len(p.TemporaryMessages) - 1; i >= 0; i-- {
+		m := p.TemporaryMessages[i]
+		if IsSpecialMessage(m, ChapterBreak) {
+			return
+		}
+		if p.TemporaryMessages[i] != nil {
+			p.TemporaryMessages = append(p.TemporaryMessages, ChapterBreak)
+			return
+		}
+	}
+	// No non-nil messages -- nothing to do.
+}
+
+// SectionBreak apends a section break to p.TemporaryMessages, unless it is
+// empty or the most recent non-nil message is already a section/chapter break.
+func (p *Player[C]) SectionBreak() {
+	for i := len(p.TemporaryMessages) - 1; i >= 0; i-- {
+		m := p.TemporaryMessages[i]
+		if IsSpecialMessage(m, ChapterBreak) || IsSpecialMessage(m, SectionBreak) {
+			return
+		}
+		if m != nil {
+			p.TemporaryMessages = append(p.TemporaryMessages, SectionBreak)
+			return
+		}
+	}
+	// No non-nil messages -- nothing to do.
+}
+
+// Simulate executes the simulation up to the start of the next turn. If the
+// simulation crashes, the game state becomes GameCrashed. This returns any
+// generated errors; if the debugging mode is 0 or greater, they also become
+// temporary messages for the next turn.
+func (p *Player[C]) Simulate() error {
+	var errs ErrorCollector
+	p.TemporaryMessages = nil
+	p.TemporaryPanels = nil
+	errs.Add(p.Rules.Run(p))
+	errs.Add(p.StartNextTurn())
+
+	if errs.HasFailure() {
+		p.State = GameCrashed
+	}
+
+	if p.DebugLevel > 0 && !errs.IsEmpty() {
+		p.ChapterBreak()
+		p.TemporaryMessages = append(p.TemporaryMessages, Msgf("%d errors and warnings:", len(errs.Errs)))
+		for i, e := range errs.Errs {
+			yikes := " "
+			if IsSeriousError(e) {
+				yikes = "!"
+			}
+			p.TemporaryMessages = append(p.TemporaryMessages, Msgf("%s[%d]:\t%v", yikes, i, e))
+		}
+	}
+	return errs.Emit()
+}
+
+// StartNextTurn increments the turn counter, resets the action counter,
+// and draws back up to full. If the player cannot take any actions after
+// drawing is complete, the game stalls. (If a drawn card would like to
+// force the player to take no actions for a turn, the best approach is to
+// make that card Urgent and make it reset ActionsRemaining to 0 after it runs.)
+func (p *Player[C]) StartNextTurn() error {
+	var errs ErrorCollector
+	p.TurnNumber++
+	p.ActionsRemaining = p.ActionsPerTurn
+	errs.Add(p.FillHand())
+	if len(p.Hand)+len(p.PermanentActions) == 0 {
+		p.State = GameStalled
+		errs.Add(Warningf("%w: no cards in hand, no permanent actions", WarningStalemate))
+	}
+	if p.ActionsRemaining == 0 {
+		p.State = GameStalled
+		errs.Add(Warningf("%w: 0 actions available in the turn", WarningStalemate))
+	}
+	return errs.Emit()
+}
+
+// FillHand draws up to the hand limit, informing cards that they have been
+// drawn. If more than a million cards refuse to enter the hand, this crashes
+// with ErrUncooperativeCards. If the deck does not have enough cards, this
+// returns WarningTooFewCards.
+func (p *Player[C]) FillHand() error {
+	failureLimit := 1000000
+	for failureLimit > 0 && p.Deck.Len() > 0 && len(p.Hand) < p.HandLimit {
+		c := p.Deck.Draw()
+		if c.Drawn(p) {
+			p.Hand = append(p.Hand, c)
+		} else {
+			failureLimit--
+		}
+	}
+
+	if len(p.Hand) >= p.HandLimit {
+		return nil
+	}
+
+	if failureLimit <= 0 {
+		return ErrUncooperativeCards
+	}
+
+	return WarningTooFewCards
+}