- Copied deepseek_v4_encoding.py from vLLM tree to encoding/
- Replaced hand-rolled prompt construction with encode_messages()
- --chat-mode → --thinking-mode (thinking|chat)
- The official encoder handles: BOS, User/Assistant tokens, thinking mode,
tool calls, and all special token placement. It can't drift.
- This is the same code path inference engines will use.
