a89e766da1
_to_rust_bytes() centralises all Python→Rust JSON serialisation:
- _json_null_clean() strips U+0000 from all string values recursively
- ensure_ascii=True guarantees no 0x00 in output bytes
- All _json() call sites migrated; mode/verbosity now .encode("ascii")
- 9 null-safety unit tests added to TestRustBytesNullSafety
Root cause: ctypes.c_char_p silently truncates at first 0x00 byte,
causing serde_json "premature end of input at column 41" on EXIT intents
with BNB-USDT leverage values. Long-term fix: Rust FFI (ptr, len) pairs.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>