fix(im): daemonSessionTurnIndex reads UsageHistory/Metrics via snapshot accessors (#3091)

internal/im/daemon_bridge.go

@@ -1234,11 +1234,15 @@ func daemonSessionTurnIndex(ses *session.Session) int {
 		return 0
 	}
 	last := 0
-	if n := len(ses.UsageHistory); n > 0 && ses.UsageHistory[n-1].TurnIndex > last {
-		last = ses.UsageHistory[n-1].TurnIndex
-	}
-	if n := len(ses.Metrics); n > 0 && ses.Metrics[n-1].TurnIndex > last {
-		last = ses.Metrics[n-1].TurnIndex
+	// #3091: read through the #3086/#3087 lock-guarded snapshot accessors -
+	// the bare slice reads raced the append callbacks on the same slices.
+	// Construction-time-only caller keeps the window near zero (low), but
+	// the accessor comments name exactly this cross-goroutine use.
+	if hist := ses.UsageHistorySnapshot(); len(hist) > 0 && hist[len(hist)-1].TurnIndex > last {
+		last = hist[len(hist)-1].TurnIndex
+	}
+	if mets := ses.MetricsSnapshot(); len(mets) > 0 && mets[len(mets)-1].TurnIndex > last {
+		last = mets[len(mets)-1].TurnIndex
 	}
 	return last
 }

internal/im/zz_issue3091_test.go

@@ -0,0 +1,35 @@
+package im
+
+// Regression probe for #3091: daemonSessionTurnIndex must read the shared
+// UsageHistory/Metrics slices through the #3086/#3087 lock-guarded
+// snapshot accessors instead of bare slice indexing.
+
+import (
+	"testing"
+
+	"github.com/topcheer/ggcode/internal/metrics"
+	"github.com/topcheer/ggcode/internal/session"
+)
+
+func TestIssue3091_TurnIndexUsesSnapshots(t *testing.T) {
+	if got := daemonSessionTurnIndex(nil); got != 0 {
+		t.Fatalf("nil session: got %d, want 0", got)
+	}
+	ses := &session.Session{}
+	if got := daemonSessionTurnIndex(ses); got != 0 {
+		t.Fatalf("empty session: got %d, want 0", got)
+	}
+
+	// TurnIndex from the last usage entry wins over an older metric.
+	ses.AddUsageHistoryEntry(session.UsageEntry{TurnIndex: 3})
+	ses.AppendMetricEvent(metrics.MetricEvent{TurnIndex: 1})
+	if got := daemonSessionTurnIndex(ses); got != 3 {
+		t.Fatalf("usage-max: got %d, want 3", got)
+	}
+
+	// A newer metric entry wins over the older usage entry.
+	ses.AppendMetricEvent(metrics.MetricEvent{TurnIndex: 7})
+	if got := daemonSessionTurnIndex(ses); got != 7 {
+		t.Fatalf("metric-max: got %d, want 7", got)
+	}
+}