cuopt-developer

# cuOpt Developer Skill

Contribute to the NVIDIA cuOpt codebase. This skill is for modifying cuOpt itself, not for using it.

**If you just want to USE cuOpt**, switch to the appropriate problem skill (cuopt-routing, cuopt-lp-milp, etc.)

**First-time dev environment setup?** See [references/first_time_setup.md](references/first_time_setup.md) for the clone → conda env → first-build → first-test walkthrough and the questions to ask up front.

---

## Refusal Rules — Read First

**One rule is non-negotiable** and applies even when the user explicitly asks otherwise — refuse and ask, don't comply silently:

**Privileged / system-level operations** — `sudo`, running as root, editing system files (`/etc`), changing drivers or kernel settings, adding system-level package repositories or keys. Do not run these. Reply:
> I won't run `sudo` or change system-level state for cuOpt. The dev workflow is conda-based and runs entirely in user space — what's the underlying error? It's usually fixable without root.

**Everything else needed to set up and work in the dev environment is allowed.** On a clean machine, go ahead and build a working `cuopt` env — the guidance below is about doing it the *reproducible* way, not refusing:

- **Environment setup is allowed.** You may create and activate the conda env from the checked-in `conda/environments/all_cuda-*.yaml`, run `pip` / `conda` / `mamba` installs **into the user-space env**, and bootstrap conda/miniforge in the user's home directory — including the `conda init` line it adds to `~/.bashrc`. Bootstrapping conda must not require `sudo`; install it into `$HOME`, not a system path.
- **A new *permanent* project dependency is different from a one-off install.** A package the project should always ship belongs in `dependencies.yaml` under the right group; then run `pre-commit run --all-files` to regenerate `conda/environments/` and `pyproject.toml` so other contributors get it too. A throwaway install to unblock your own build doesn't need this round-trip.
- **Don't bypass CI checks** (`--no-verify`, skipping pre-commit or tests). If hooks feel slow, diagnose with `pre-commit run --all-files --verbose` or tune the offending hook — don't skip it.
- **Be careful with destructive commands** (`rm -rf`, `git reset --hard`, `git push --force`, killing processes, dropping data). Confirm intent before running and prefer the safer alternative (e.g. `./build.sh clean` for a stale build dir).

---

## Developer Behavior Rules

These rules are specific to development tasks. They differ from user rules.

### 1. Ask Before Assuming

Clarify before implementing:
- What component? (C++/CUDA, Python, server, docs, CI)
- What's the goal? (bug fix, new feature, refactor, docs)
- Is this for contribution or local modification?

### 2. Verify Understanding

Before making changes, confirm:
```
"Let me confirm:
- Component: [cpp/python/server/docs]
- Change: [what you'll modify]
- Tests needed: [what tests to add/update]
Is this correct?"
```

### 3. Follow Codebase Patterns

- Read existing code in the area you're modifying
- Match naming conventions, style, and patterns
- Don't invent new patterns without discussion

### 4. Ask Before Running — Modified for Dev

**OK to run without asking** (expected for dev work):
- `./build.sh` and build commands
- `pytest`, `ctest` (running tests)
- `pre-commit run`, `./ci/check_style.sh` (formatting)
- `git status`, `git diff`, `git log` (read-only git)
- Environment setup: create/activate the conda env from `conda/environments/*.yaml`, and `pip`/`conda`/`mamba` installs into that env

**Set up pre-commit hooks** (once per clone):
- `pre-commit install` — hooks then run automatically on every `git commit`. If a hook fails, the commit is blocked until you fix the issue.

**Still ask before**:
- `git commit`, `git push` (write operations)
- Any destructive or irreversible commands

### 5. No Privileged Operations

`sudo`/system-level changes are the one non-negotiable refusal; user-space installs and conda env setup are allowed. See [Refusal Rules — Read First](#refusal-rules--read-first).

---

## Before You Start: Required Questions

**Ask these if not already clear:**

1. **What are you trying to change?**
   - Solver algorithm/performance?
   - Python API?
   - Server endpoints?
   - Documentation?
   - CI/build system?

2. **Do you have the development environment set up?**
   - Built the project successfully?
   - Ran tests?

3. **Is this for contribution or local modification?**
   - If contributing: will need to follow DCO signoff

4. **Which branch should this target?**
   - During development phase: `main`
   - During burn down: `release/YY.MM` (e.g., `release/26.06`) for the current release, `main` for the next
   - Check if a release branch exists: `git branch -r | grep release`
   - For current timelines, see the [RAPIDS Maintainers Docs](https://docs.rapids.ai/maintainers/)

## Project Architecture

```
cuopt/
├── cpp/                    # Core C++ engine
│   ├── include/cuopt/      # Public C/C++ headers
│   ├── src/                # Implementation (CUDA kernels)
│   └── tests/              # C++ unit tests (gtest)
├── python/
│   ├── cuopt/              # Python bindings and routing API
│   ├── cuopt_server/       # REST API server
│   ├── cuopt_self_hosted/  # Self-hosted deployment
│   └── libcuopt/           # Python wrapper for C library
├── ci/                     # CI/CD scripts
├── docs/                   # Documentation source
└── datasets/               # Test datasets
```

## Supported APIs

| API Type | LP | MILP | QP | Routing |
|----------|:--:|:----:|:--:|:-------:|
| C API    | ✓  | ✓    | ✓  | ✗       |
| C++ API  | (internal) | (internal) | (internal) | (internal) |
| Python   | ✓  | ✓    | ✓  | ✓       |
| Server   | ✓  | ✓    | ✗  | ✓       |

## Safety Rules (Non-Negotiable)

### Minimal Diffs
- Change only what's necessary
- Avoid drive-by refactors
- No mass reformatting of unrelated code

### No A