fix: silently cache images in group rooms without mention

Same pattern as files: download and cache in _recent_images without
responding. When user next @mentions the bot, the cached image is
available as context. Applied to both plain and encrypted image handlers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bot.py

@@ -2187,23 +2187,20 @@ class Bot:
 
         await self._load_room_settings(room.room_id)
 
-        # In DMs respond to all images; in groups only if bot was recently @mentioned
+        # In DMs respond to all images; in groups, silently cache (respond only if mentioned)
         is_dm = room.member_count == 2
+        group_mentioned = False
         if not is_dm:
-            # Check if bot was @mentioned in the image body (caption) or skip
             body = (event.body or "").strip()
             bot_display = self.client.user_id.split(":")[0].lstrip("@")
-            # Also match display name (e.g. 'Claude') since Element uses it in mentions
             bot_displayname = (getattr(self, '_display_name', '') or bot_display).lower()
             body_lower = body.lower()
-            mentioned = (
+            group_mentioned = (
                 BOT_USER in body
                 or f"@{bot_display}" in body_lower
                 or bot_display.lower() in body_lower
                 or bot_displayname in body_lower
             )
-            if not mentioned:
-                return
 
         if not self.llm:
             await self._send_text(room.room_id, "LLM not configured (LITELLM_BASE_URL not set).")
@@ -2235,6 +2232,11 @@ class Bot:
         # Cache image for follow-up text messages
         self._recent_images[room.room_id] = (b64_data, mime_type, time.time())
 
+        # In group rooms without mention, silently cache — respond on next @mention
+        if not is_dm and not group_mentioned:
+            logger.info("Silently cached image in group room %s", room.room_id)
+            return
+
         await self.client.room_typing(room.room_id, typing_state=True)
         try:
             reply = await self._respond_with_ai(room, text, sender=event.sender, image_data=(b64_data, mime_type))
@@ -2266,14 +2268,12 @@ class Bot:
             # Also match display name (e.g. 'Claude') since Element uses it in mentions
             bot_displayname = (getattr(self, '_display_name', '') or bot_display).lower()
             body_lower = body.lower()
-            mentioned = (
+            group_mentioned = (
                 BOT_USER in body
                 or f"@{bot_display}" in body_lower
                 or bot_display.lower() in body_lower
                 or bot_displayname in body_lower
             )
-            if not mentioned:
-                return
 
         if not self.llm:
             await self._send_text(room.room_id, "LLM not configured (LITELLM_BASE_URL not set).")
@@ -2303,6 +2303,11 @@ class Bot:
         # Cache image for follow-up text messages
         self._recent_images[room.room_id] = (b64_data, mime_type, time.time())
 
+        # In group rooms without mention, silently cache — respond on next @mention
+        if not is_dm and not group_mentioned:
+            logger.info("Silently cached encrypted image in group room %s", room.room_id)
+            return
+
         await self.client.room_typing(room.room_id, typing_state=True)
         try:
             reply = await self._respond_with_ai(room, text, sender=event.sender, image_data=(b64_data, mime_type))