# Engine map: Python `rst_engine` vs Rust `RRT_Execution_Engine`
Two codebases serve different layers of the same research program. **Do not assume numerical identity** between them unless a parity test or config flag explicitly says so.
## Python: `rst_engine/` (workspace root)
**Role:** Single implementation of continuous RST core maths used by vault scripts and evaluations.
- **Fidelity and triangle:** `mu_rst`, `solve_omega`, `volume_ln_ball`, calibration helpers.
- **Consumers:** `expanded theory/python calculations/*`, `expanded theory applied/*` application scripts, **`expanded theory/sparc evaluation/`** (e.g. `mu_rst`, acceleration solvers).
- **Graph / axiom experiments:** `rst_engine/axiom_pure.py` — discrete pure-axiom dynamics in Python (Micro-Graph Generator, sweeps, fits).
**Strength:** Fast iteration, numpy/scipy, SPARC notebooks, sovereign-chain capstone scripts.
## Rust: `RRT_Execution_Engine/`
**Role:** High-performance discrete substrate (e.g. `axiom_pure_engine`), **reality_mapper** CLI modes such as **`lab_calculator`**, large-\(N\) quenches, JSON/`geometry_bridge` exports, Obsidian exports under configured paths.
**Strength:** Heavy runs (e.g. large node counts, long quenches) and packaged lab YAML.
## Parity
- **Not automatic.** Event ordering, thermal schedule, sweep caps, and RNG can differ unless **`python_parity_timeline`** (or equivalent) is enabled in the Rust lab config **and** validated against a reference Python trace.
- **When outputs differ:** Check whether observables are comparable (e.g. Python fitted \(n\) from a **noise sweep** vs Rust **spectral \(d_s\)** on the LCC after quench — different objects).
## Diagram
```mermaid
flowchart LR
subgraph py [Python_vault]
rst_engine[rst_engine]
sparc[sparc_evaluation]
capstone[capstone_scripts]
end
subgraph rust [Rust_engine]
axiom[axiom_pure_engine]
lab[lab_calculator]
end
rst_engine --> sparc
rst_engine --> capstone
axiom --> lab
py -. "parity_tests_or_config" .- rust
```
## See also
- **[`RUNBOOK.md`](../RUNBOOK.md)** — install and `pytest` from repo root.
- **[`expanded theory applied/Implementation status and problems.md`](../expanded%20theory%20applied/Implementation%20status%20and%20problems.md)** — SPARC + `rst_engine` integration note.