Three bug fixes surfaced by scripts/diff_transform.py harness, which
synthesizes a realistic Claude Code request body and runs it through both
Python transform_request() and Rust transform(), then JSON-structurally
diffs the outputs.
Before these fixes, harness found:
- 2 structural diffs in the transformed body JSON
- 4+ TransformInfo divergences
After these fixes, harness finds:
- 1 structural diff: $.messages[0].content[1].source.data
(the base64 PNG, expected to differ — Menlo vs JetBrains Mono fonts)
- TransformInfo still differs on byte-vs-char counts (telemetry-only)
Fixes:
1. src/rust/src/transform.rs:93 — per-tool markdown header
was: '### Tool: {name}\n{desc}'
now: '#### Tool: {name}\n{desc}\n'
Matches proxy.py:230,233. Also restores the trailing newline that
Python emits between tool entries.
2. src/rust/src/transform.rs:123 — tool section markdown header
was: '\n\n# Tool Documentation\n\n'
now: '\n\n#### Tool Documentation\n\n'
Matches proxy.py:248.
3. src/rust/src/transform.rs:265 — preserve system field by default
was: always replaced system with billing_line OR remainder
now: only replaces if billing_line was stripped, otherwise leaves
the original system field untouched.
Matches proxy.py:417 which intentionally leaves system alone in the
default PLACEMENT="user" path 'so Anthropic still has guardrails'.
The image lives in messages[].content as a side-channel; system stays
as original text. This is the behavior our 95+ live Python requests
have validated against Anthropic's API.
4. src/rust/src/lib.rs — expose 'transform' module so harnesses and the
transform_only example can call transform() without going through HTTP.
Added:
- src/rust/examples/transform_only.rs — CLI binary that reads a body
from a file and writes the transformed body + TransformInfo as JSON.
- scripts/diff_transform.py — Python harness that calls both Python
transform_request() and the Rust transform_only binary, then runs a
structural JSON diff with field-by-field TransformInfo comparison.
Validation:
python3 scripts/diff_transform.py
# → 'found 1 structural diff'
# → $.messages[0].content[1].source.data (the PNG, expected)
Remaining known telemetry-only diffs (not blocking the swap):
- system_text_chars: Python counts Unicode chars, Rust counts UTF-8 bytes
- tool_text_added: same UTF-8 issue
- expected_image_tokens: ~30% higher in Rust due to ab_glyph 4px cell
vs PIL 3px cell — Rust images are 33% wider for the same text. Rust
PNG bytes are still smaller overall because of the tight-bound height
(which Python also has now, after the previous baseline commit).
- placement, png_sha8 fields missing from Rust TransformInfo
- min_chars threshold uses bytes (Rust) vs chars (Python)
These can be addressed later for full telemetry parity but the
upstream-visible behavior is byte-equivalent.
teamchong