feat(rewind): add save/load for RewindStore persistence

scripts/lib/rewind/store.py

@@ -16,9 +16,11 @@
 """
 from __future__ import annotations
 import hashlib
+import json
 import time
 from collections import OrderedDict
 from dataclasses import dataclass
+from pathlib import Path
 from typing import Optional
 
 
@@ -87,3 +89,74 @@ def size(self) -> int:
 
     def clear(self) -> None:
         self._cache.clear()
+
+    # ------------------------------------------------------------------
+    # Persistence
+    # ------------------------------------------------------------------
+
+    def save(self, path: str | Path) -> int:
+        """Persist the current cache to a JSON file.
+
+        Entries that have exceeded their TTL are not saved.  Returns the
+        number of entries written.
+
+        Args:
+            path: Destination file path (will be created or overwritten).
+
+        Returns:
+            Number of entries persisted.
+        """
+        now = time.monotonic()
+        entries: dict[str, dict] = {}
+        for hash_id, entry in self._cache.items():
+            age = now - entry.stored_at
+            if age <= self.ttl_seconds:
+                entries[hash_id] = {
+                    "original": entry.original,
+                    "compressed": entry.compressed,
+                    "remaining_ttl": round(self.ttl_seconds - age, 1),
+                    "original_tokens": entry.original_tokens,
+                    "compressed_tokens": entry.compressed_tokens,
+                }
+        Path(path).write_text(
+            json.dumps(entries, ensure_ascii=False, indent=2),
+            encoding="utf-8",
+        )
+        return len(entries)
+
+    def load(self, path: str | Path) -> int:
+        """Restore cache entries from a previously saved JSON file.
+
+        Loaded entries are merged into the current cache (existing entries
+        are preserved).  Each loaded entry's TTL is set to its
+        ``remaining_ttl`` from the save file — entries that would already
+        be expired are skipped.
+
+        Args:
+            path: Source file path.
+
+        Returns:
+            Number of entries loaded.
+        """
+        data = json.loads(Path(path).read_text(encoding="utf-8"))
+        loaded = 0
+        now = time.monotonic()
+        for hash_id, blob in data.items():
+            remaining = blob.get("remaining_ttl", 0)
+            if remaining <= 0:
+                continue
+            if hash_id in self._cache:
+                continue  # don't overwrite live entries
+            entry = CacheEntry(
+                original=blob["original"],
+                compressed=blob.get("compressed", ""),
+                stored_at=now - (self.ttl_seconds - remaining),
+                original_tokens=blob.get("original_tokens", 0),
+                compressed_tokens=blob.get("compressed_tokens", 0),
+            )
+            self._cache[hash_id] = entry
+            loaded += 1
+        # Enforce max_entries after load
+        while len(self._cache) > self.max_entries:
+            self._cache.popitem(last=False)
+        return loaded