2 files changed, 75 insertions, 3 deletions
diff --git a/internal/game/hacking/liars_dice.go b/internal/game/hacking/liars_dice.go
index 1dd27b6..8e21b94 100644
--- a/internal/game/hacking/liars_dice.go
+++ b/internal/game/hacking/liars_dice.go
@@ -175,7 +175,7 @@ func (l *LiarsDiceGame) doCall(player bool) (string, bool, bool) {
 		}
 	}
 
-	return l.checkGameOver(sb)
+	return l.checkGameOver(&sb)
 }
 
 func (l *LiarsDiceGame) doExact() (string, bool, bool) {
@@ -202,10 +202,14 @@ func (l *LiarsDiceGame) doExact() (string, bool, bool) {
 		l.playerLost++
 	}
 
-	return l.checkGameOver(sb)
+	return l.checkGameOver(&sb)
 }
 
-func (l *LiarsDiceGame) checkGameOver(sb strings.Builder) (string, bool, bool) {
+// checkGameOver resolves a completed challenge/exact exchange. The builder is
+// passed BY POINTER: it already holds the resolution text, and copying a
+// non-zero strings.Builder by value panics — a panic here runs on the game
+// owner goroutine, which has no recovery, so it would terminate the server.
+func (l *LiarsDiceGame) checkGameOver(sb *strings.Builder) (string, bool, bool) {
 	if len(l.playerDice) == 0 {
 		sb.WriteString("\nYou've lost all your fragments. Connection terminated.")
 		l.gameOver = true
diff --git a/internal/game/hacking/liars_dice_test.go b/internal/game/hacking/liars_dice_test.go
new file mode 100644
index 0000000..59ebb92
--- /dev/null
+++ b/internal/game/hacking/liars_dice_test.go
@@ -0,0 +1,68 @@
+package hacking
+
+import (
+	"strings"
+	"testing"
+)
+
+// Regression: round resolution (challenge and exact calls) passed an
+// already-used strings.Builder BY VALUE into checkGameOver, panicking with
+// "illegal use of non-zero Builder copied by value" on ordinary input — a
+// forced challenge resolves on the very first bid. A panic here runs on the
+// game owner goroutine, which has no recovery, so it terminated the server.
+// See building_guide/concurrency.md for the owner's no-recovery guarantee.
+
+func TestLiarsDiceForcedChallengeDoesNotPanic(t *testing.T) {
+	g := NewLiarsDiceGame()
+	g.Init(1)
+	// An impossible bid deterministically forces an immediate AI challenge.
+	out, _, _ := g.HandleInput("bid 100 6")
+	if !strings.Contains(out, "Actual count") {
+		t.Fatalf("challenge output missing the reveal: %q", out)
+	}
+	if !strings.Contains(out, "You lose a fragment") && !strings.Contains(out, "System loses a fragment") {
+		t.Fatalf("challenge did not resolve a fragment loss: %q", out)
+	}
+}
+
+func TestLiarsDiceCallAndExactResolveWithoutPanic(t *testing.T) {
+	// Call path: bid, let the system raise, then challenge it.
+	g := NewLiarsDiceGame()
+	g.Init(1)
+	if out, _, _ := g.HandleInput("bid 2 3"); out == "" {
+		t.Fatal("opening bid produced no output")
+	}
+	if out, _, _ := g.HandleInput("call"); out == "" {
+		t.Fatal("call produced no output")
+	}
+
+	// Exact path: bid, let the system raise, then claim exact.
+	g = NewLiarsDiceGame()
+	g.Init(1)
+	if out, _, _ := g.HandleInput("bid 2 3"); out == "" {
+		t.Fatal("opening bid produced no output")
+	}
+	if out, _, _ := g.HandleInput("exact"); out == "" {
+		t.Fatal("exact produced no output")
+	}
+}
+
+func TestLiarsDiceFullLossGameResolvesWithoutPanic(t *testing.T) {
+	// Bid high enough that the system always calls and the player always
+	// loses a fragment, driving the game to its terminal resolution.
+	g := NewLiarsDiceGame()
+	g.Init(1)
+	for i := 0; i < 10; i++ {
+		out, done, won := g.HandleInput("bid 100 6")
+		if done {
+			if won {
+				t.Fatal("all-in losing bids cannot win")
+			}
+			return
+		}
+		if out == "" {
+			t.Fatal("round produced no output")
+		}
+	}
+	t.Fatal("game did not terminate within 10 forced-loss rounds")
+}