riddle/trivia: persist dedup caches to disk so restarts don't reset them

riddle_cache.json: stores last 30 riddle texts + answers
trivia_cache.json: stores last 20 questions per category

Both files are capped at their respective maxes so they never grow
unboundedly. Loaded on startup, saved after each new question.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

matrixbot/commands.py

@@ -6,6 +6,7 @@ import time
 import logging
 from collections import Counter
 from datetime import datetime
+from pathlib import Path
 
 import aiohttp
 
@@ -1006,8 +1007,25 @@ _TRIVIA_FALLBACKS: dict[str, list[dict]] = {
 
 
 # Per-category cache of recently asked question texts (avoids duplicates)
-_trivia_recent: dict[str, list[str]] = {}
 _TRIVIA_RECENT_MAX = 20
+_TRIVIA_CACHE_FILE = Path("trivia_cache.json")
+
+
+def _load_trivia_cache() -> dict[str, list[str]]:
+    try:
+        return json.loads(_TRIVIA_CACHE_FILE.read_text())
+    except Exception:
+        return {}
+
+
+def _save_trivia_cache(cache: dict[str, list[str]]) -> None:
+    try:
+        _TRIVIA_CACHE_FILE.write_text(json.dumps(cache, indent=2))
+    except Exception as e:
+        logger.warning("Failed to save trivia cache: %s", e)
+
+
+_trivia_recent: dict[str, list[str]] = _load_trivia_cache()
 
 
 async def _generate_trivia_question(category: str) -> dict | None:
@@ -1072,6 +1090,7 @@ async def _generate_trivia_question(category: str) -> dict | None:
                     bucket.append(parsed["q"])
                     if len(bucket) > _TRIVIA_RECENT_MAX:
                         bucket.pop(0)
+                    _save_trivia_cache(_trivia_recent)
                     return parsed
     except Exception:
         pass
@@ -1783,9 +1802,26 @@ async def cmd_wyr(client: AsyncClient, room_id: str, sender: str, args: str):
 # ---------------------------------------------------------------------------
 
 _RIDDLE_ACTIVE: dict[str, dict] = {}
-_riddle_recent: list[str] = []       # past riddle texts
-_riddle_recent_answers: list[str] = []  # past answers (lowercase)
 _RIDDLE_RECENT_MAX = 30
+_RIDDLE_CACHE_FILE = Path("riddle_cache.json")
+
+
+def _load_riddle_cache() -> tuple[list[str], list[str]]:
+    try:
+        data = json.loads(_RIDDLE_CACHE_FILE.read_text())
+        return data.get("riddles", []), data.get("answers", [])
+    except Exception:
+        return [], []
+
+
+def _save_riddle_cache(riddles: list[str], answers: list[str]) -> None:
+    try:
+        _RIDDLE_CACHE_FILE.write_text(json.dumps({"riddles": riddles, "answers": answers}, indent=2))
+    except Exception as e:
+        logger.warning("Failed to save riddle cache: %s", e)
+
+
+_riddle_recent, _riddle_recent_answers = _load_riddle_cache()
 
 
 async def _generate_riddle() -> dict | None:
@@ -1842,6 +1878,7 @@ async def _generate_riddle() -> dict | None:
                     _riddle_recent_answers.append(answer.lower())
                     if len(_riddle_recent_answers) > _RIDDLE_RECENT_MAX:
                         _riddle_recent_answers.pop(0)
+                    _save_riddle_cache(_riddle_recent, _riddle_recent_answers)
                     return {"riddle": riddle, "answer": answer}
     except Exception as e:
         logger.error(f"riddle generation error: {e}", exc_info=True)