step 1: lock public api and pure core

src/dpg_map/cache.py

@@ -1 +1,36 @@
 """Memory and disk cache helpers."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from pathlib import Path
+
+
+@dataclass(frozen=True, slots=True)
+class CacheStats:
+    """Public cache statistics snapshot."""
+
+    memory_tiles: int = 0
+    memory_max_tiles: int = 0
+    memory_hits: int = 0
+    memory_misses: int = 0
+    disk_bytes: int = 0
+    disk_max_bytes: int | None = None
+    disk_hits: int = 0
+    disk_misses: int = 0
+    disk_path: Path | None = None
+
+
+@dataclass(slots=True)
+class MemoryCacheConfig:
+    """Initial memory cache configuration."""
+
+    max_tiles: int = 512
+
+
+@dataclass(slots=True)
+class DiskCacheConfig:
+    """Initial persistent disk cache configuration."""
+
+    path: Path | None = None
+    max_bytes: int | None = 2_000_000_000