Initial parallelization attempt

AGENTS.md

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+# LibRay — Agent Quick Reference
+# Important
+Make sure to use the virtual environment in .venv and not global pip.
+
+## Repo
+- Python 3 CLI tool for decrypting/encrypting/examining PS3 Blu-Ray ISOs
+- Entry point: `libray/libray` (also `libray/libray.py`, identical copy)
+- Package: `libray/` — modules: `core.py` (main logic), `iso.py` (ISO parsing), `ird.py` (IRD parsing), `sfo.py` (PARAM.SFO)
+- Tests: `tests/` — `test_iso.py`, `test_interface.py` (interface test is currently skipped/broken)
+- Tools: `tools/keys2db.py` (builds `libray/data/keys.db` from redump keys), `tools/rpcs3.py` (fetches compat data)
+
+## Commands
+- Install deps: `pip install -r requirements.txt`
+- Run tests: `python -m unittest discover -b`
+- Build sdist + wheel: `python3 setup.py sdist bdist_wheel`
+- Publish: `twine upload dist/*`
+
+## Parallelization
+- Decrypt and re-encrypt support multi-threading via `-p`/`--threads` CLI argument
+- Default: auto-detects CPU core count via `os.cpu_count()`
+- Each sector is independently decrypted (per-sector IV in AES-CBC), making it embarrassingly parallel
+- Uses `concurrent.futures.ThreadPoolExecutor` (threads, not processes, since pycryptodome releases the GIL)
+- Unencrypted regions are always copied sequentially (no crypto needed)
+- Sector data is read upfront into memory, then processed in parallel, then written in order
+
+## Gotchas
+- **Crypto package conflict**: `pycrypto`/`crypto` will break `pycryptodome`. If `ImportError: No module named Crypto.Cipher`, run:
+  ```
+  pip uninstall crypto pycrypto && pip install pycryptodome
+  ```
+- **keys.db is generated**, not committed. Build it with `python3 tools/keys2db.py` (requires keys in `tools/keys/`). It's listed in `.gitignore` via `libray/data/*.db`.
+- **`libray/__init__.py`** dynamically imports all submodules via `pkgutil.walk_packages` — don't expect explicit imports.
+- **`test_interface.py`** is skipped (`@unittest.skip('currently broken')`) — the interface test won't run.
+- `.editorconfig` enforces 4-space indent for `.py`, 2-space for `.yml`/`.yaml`.
+- No linting/typechecking config exists — plain `unittest`, no pytest, no pre-commit.