diff --git a/cmd/olliesrv/internal/agent/history.go b/cmd/olliesrv/internal/agent/history.go
index b7afdc4..176a14a 100644
--- a/cmd/olliesrv/internal/agent/history.go
+++ b/cmd/olliesrv/internal/agent/history.go
@@ -2,7 +2,6 @@ package agent
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"os"
 	"strings"
@@ -437,8 +436,10 @@ func (s *History) stripCold(ctx context.Context, b backend.Backend) (backend.Usa
 	}
 	estimated := !reported
 
-	summaries := make(map[string]string)
-	json.Unmarshal([]byte(resp.String()), &summaries)
+	summaries, err := parseColdSummaries(resp.String())
+	if err != nil {
+		return usage, estimated
+	}
 
 	// Apply summaries back into history.
 	for _, it := range items {
diff --git a/cmd/olliesrv/internal/agent/history_summary.go b/cmd/olliesrv/internal/agent/history_summary.go
new file mode 100644
index 0000000..197aeda
--- /dev/null
+++ b/cmd/olliesrv/internal/agent/history_summary.go
@@ -0,0 +1,26 @@
+package agent
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+)
+
+func parseColdSummaries(content string) (map[string]string, error) {
+	content = strings.TrimSpace(content)
+	if strings.HasPrefix(content, "```") && strings.HasSuffix(content, "```") {
+		content = strings.TrimSpace(strings.TrimSuffix(strings.TrimPrefix(content, "```"), "```"))
+		if newline := strings.IndexByte(content, '\n'); newline >= 0 && strings.EqualFold(strings.TrimSpace(content[:newline]), "json") {
+			content = strings.TrimSpace(content[newline+1:])
+		}
+	}
+
+	var summaries map[string]string
+	if err := json.Unmarshal([]byte(content), &summaries); err != nil {
+		return nil, fmt.Errorf("parse cold summaries: %w", err)
+	}
+	if summaries == nil {
+		return nil, fmt.Errorf("parse cold summaries: expected JSON object")
+	}
+	return summaries, nil
+}
diff --git a/cmd/olliesrv/internal/agent/history_summary_test.go b/cmd/olliesrv/internal/agent/history_summary_test.go
new file mode 100644
index 0000000..51edc0b
--- /dev/null
+++ b/cmd/olliesrv/internal/agent/history_summary_test.go
@@ -0,0 +1,29 @@
+package agent
+
+import "testing"
+
+func TestParseColdSummariesJSON(t *testing.T) {
+	got, err := parseColdSummaries(`{"0":"summary","1":"another"}`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got["0"] != "summary" || got["1"] != "another" {
+		t.Fatalf("unexpected summaries: %#v", got)
+	}
+}
+
+func TestParseColdSummariesFencedJSON(t *testing.T) {
+	got, err := parseColdSummaries("```json\n{\"0\":\"summary\"}\n```")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got["0"] != "summary" {
+		t.Fatalf("unexpected summaries: %#v", got)
+	}
+}
+
+func TestParseColdSummariesRejectsInvalidJSON(t *testing.T) {
+	if _, err := parseColdSummaries("not JSON"); err == nil {
+		t.Fatal("parseColdSummaries accepted invalid JSON")
+	}
+}