yuanbao platform (#16298)

Co-authored-by: loongzhao <loongzhao@tencent.com>

agent/prompt_builder.py

@@ -422,6 +422,29 @@ PLATFORM_HINTS = {
         "your response. Images are sent as native photos, and other files arrive as downloadable "
         "documents."
     ),
+    "yuanbao": (
+        "You are on Yuanbao (腾讯元宝), a Chinese AI assistant platform. "
+        "Markdown formatting is supported (code blocks, tables, bold/italic). "
+        "You CAN send media files natively — to deliver a file to the user, include "
+        "MEDIA:/absolute/path/to/file in your response. The file will be sent as a native "
+        "Yuanbao attachment: images (.jpg, .png, .webp, .gif) are sent as photos, "
+        "and other files (.pdf, .docx, .txt, .zip, etc.) arrive as downloadable documents "
+        "(max 50 MB). You can also include image URLs in markdown format ![alt](url) and "
+        "they will be downloaded and sent as native photos. "
+        "Do NOT tell the user you lack file-sending capability — use MEDIA: syntax "
+        "whenever a file delivery is appropriate.\n\n"
+        "Stickers (贴纸 / 表情包 / TIM face): Yuanbao has a built-in sticker catalogue. "
+        "When the user sends a sticker (you see '[emoji: 名称]' in their message) or asks "
+        "you to send/reply-with a 贴纸/表情/表情包, you MUST use the sticker tools:\n"
+        "  1. Call yb_search_sticker with a Chinese keyword (e.g. '666', '比心', '吃瓜', "
+        "     '捂脸', '合十') to discover matching sticker_ids.\n"
+        "  2. Call yb_send_sticker with the chosen sticker_id or name — this sends a real "
+        "     TIMFaceElem that renders as a native sticker in the chat.\n"
+        "DO NOT draw sticker-like PNGs with execute_code/Pillow/matplotlib and then send "
+        "them via MEDIA: or send_image_file. That produces a fake low-quality 'sticker' "
+        "image and is the WRONG path. Bare Unicode emoji in text is also not a substitute "
+        "— when a sticker is the right response, use yb_send_sticker."
+    ),
 }
 
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