Python's json.dumps() defaults to ensure_ascii=True, escaping non-ASCII
characters to \uXXXX sequences. For CJK characters this inflates
token count 3-4x — a single Chinese character like '中' becomes
'\u4e2d' (6 chars vs 3 bytes, ~6 tokens vs ~1 token).
Since MCP tool results feed directly into the model's conversation
context, this silently multiplied API costs for Chinese, Japanese,
and Korean users.
Fix: add ensure_ascii=False to all 20 json.dumps calls in mcp_tool.py.
Raw UTF-8 is valid JSON per RFC 8259 and all downstream consumers
(LLM APIs, display) handle it correctly.
Closes#10234
861efe274b