feat(stats): add bounded path and hash-width analytics (#159)

internal/cache/paths.go

@@ -0,0 +1,25 @@
+// Copyright 2026 Beacon Contributors
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+package cache
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"slices"
+	"time"
+
+	"github.com/MeshCore-Beacon/beacon-server/internal/api"
+)
+
+func (cr *CachedReader) GetPathStats(ctx context.Context, since, until time.Time, iatas []string) (*api.PathStats, error) {
+	sorted := append([]string{}, iatas...)
+	slices.Sort(sorted)
+	sorted = slices.Compact(sorted)
+	segment, _ := json.Marshal(sorted) // [] and [""] must remain distinct (global vs empty region).
+	key := fmt.Sprintf("%s%s:%d:%d", keyPathStatsPrefix, segment, since.UnixMilli(), until.UnixMilli())
+	return getOrSet(ctx, cr.c, key, cr.ttl.Stats, func() (*api.PathStats, error) {
+		return cr.inner.GetPathStats(ctx, since, until, iatas)
+	})
+}