feat(notion-search): add SHA256-keyed JSON file cache

Cache layer for rerank results. Key is SHA256 of query + sorted
candidate IDs, so changing the candidate set automatically invalidates.
1-day TTL by default; corrupted cache files are silently dropped.

5 tests cover hit, miss, different-candidates, TTL expiry, corruption.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

custom-skills/31-notion-organizer/code/scripts/_search_cache.py

@@ -0,0 +1,69 @@
+"""Filesystem cache for rerank results, keyed by SHA256(query + candidate_ids)."""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import time
+from pathlib import Path
+from typing import List, Optional
+
+DEFAULT_CACHE_DIR = Path.home() / ".cache" / "notion-search"
+DEFAULT_TTL_SECONDS = 86400  # 24 hours
+
+
+def _cache_key(query: str, candidate_ids: List[str]) -> str:
+    payload = f"{query}|{','.join(sorted(candidate_ids))}"
+    return hashlib.sha256(payload.encode("utf-8")).hexdigest()
+
+
+def cache_get(
+    query: str,
+    candidate_ids: List[str],
+    *,
+    cache_dir: Path = DEFAULT_CACHE_DIR,
+    ttl_seconds: int = DEFAULT_TTL_SECONDS,
+) -> Optional[List]:
+    """Return cached results if file exists and is fresh, else None.
+
+    Corrupted cache files are silently treated as misses (and removed).
+    """
+    key = _cache_key(query, candidate_ids)
+    path = cache_dir / f"{key}.json"
+    if not path.exists():
+        return None
+
+    try:
+        data = json.loads(path.read_text(encoding="utf-8"))
+    except (json.JSONDecodeError, OSError):
+        try:
+            path.unlink()
+        except OSError:
+            pass
+        return None
+
+    cached_at = data.get("cached_at_epoch", 0)
+    if time.time() - cached_at > ttl_seconds:
+        return None
+
+    return data.get("results")
+
+
+def cache_put(
+    query: str,
+    candidate_ids: List[str],
+    results: List,
+    *,
+    cache_dir: Path = DEFAULT_CACHE_DIR,
+) -> None:
+    """Write results to cache. Creates cache_dir if missing."""
+    cache_dir.mkdir(parents=True, exist_ok=True)
+    key = _cache_key(query, candidate_ids)
+    path = cache_dir / f"{key}.json"
+    payload = {
+        "query": query,
+        "candidate_ids": list(candidate_ids),
+        "results": results,
+        "cached_at_epoch": time.time(),
+    }
+    path.write_text(json.dumps(payload, ensure_ascii=False, indent=2), encoding="utf-8")