fix: rotate challenge each session

Stop hook clears active.challenge after reporting it.
Start hook assigns a random challenge from the buddy's pool if none is set.
Result: fresh challenge every session, no stale repeat.

hooks-handlers/session-start.sh

@@ -101,6 +101,20 @@ if ch:
     echo "${ctx}"
 }
 
+# Assign a fresh challenge if none is set
+python3 << PYEOF
+import json, random
+catalog = json.load(open('${CATALOG}'))
+active_file = '${ACTIVE_FILE}'
+active = json.load(open(active_file))
+buddy_id = active.get('buddymon_id')
+if buddy_id and not active.get('challenge'):
+    pool = catalog.get('buddymon', {}).get(buddy_id, {}).get('challenges', [])
+    if pool:
+        active['challenge'] = random.choice(pool)
+        json.dump(active, open(active_file, 'w'), indent=2)
+PYEOF
+
 CONTEXT=$(build_context)
 
 # Escape for JSON

hooks-handlers/session-stop.sh

@@ -87,12 +87,13 @@ print('\n'.join(lines))
 PYEOF
 )
 
-# Reset session XP counter for next session (keep total in roster)
+# Reset session XP + clear challenge so next session assigns a fresh one
 python3 << PYEOF
 import json
 active_file = '${BUDDYMON_DIR}/active.json'
 active = json.load(open(active_file))
 active['session_xp'] = 0
+active['challenge'] = None
 json.dump(active, open(active_file, 'w'), indent=2)
 PYEOF