fix: improve show handling, cache validation and tests

Add extensive tests for the `show` command (happy path, empty/expired/malformed cache, out-of-range, zero/negative indices) and a test helper to write cache fixtures. Harden twitter_cli.cache._load_cache to validate payload types (dict/tweets list), filter non-dict entries, and treat malformed payloads as empty; also handle missing tweet id when resolving an index. Refactor CLI output logic by extracting _emit_tweet_detail and reuse it for both `tweet` and `show`; enforce 1-based indices for `show` via click.IntRange(1) and expand the "no cached results" error text to mention other list commands. These changes improve robustness against corrupted caches and increase test coverage for cache-based behavior.

twitter_cli/cache.py

@@ -38,9 +38,14 @@ def _load_cache() -> Optional[List[dict]]:
         if not _CACHE_FILE.exists():
             return None
         payload = json.loads(_CACHE_FILE.read_text(encoding="utf-8"))
+        if not isinstance(payload, dict):
+            return None
         if time.time() - payload.get("created_at", 0) > _TTL:
             return None
-        return payload.get("tweets", [])
+        entries = payload.get("tweets", [])
+        if not isinstance(entries, list):
+            return None
+        return [e for e in entries if isinstance(e, dict)]
     except (OSError, json.JSONDecodeError):
         return None
 
@@ -52,7 +57,8 @@ def get_tweet_id_by_index(index: int) -> Optional[str]:
         return None
     for entry in entries:
         if entry.get("index") == index:
-            return str(entry["id"])
+            tweet_id = entry.get("id")
+            return str(tweet_id) if tweet_id is not None else None
     return None