Release v0.6.0: fix stim_compat doc drift, version bump across all metadata

- README.md / PYPI_README.md: fix Stim workflow example that imported
  stim_circuit_to_check_matrix, a function removed since 0.5.9 and
  superseded by from_stim_detector_error_model. Verified by AST-parsing
  every documented import against the real module surface.
- Bump version to 0.6.0 across pyproject.toml, Cargo.toml, Cargo.lock,
  python/qector_decoder_v3/__init__.py, CITATION.cff, codemeta.json, and
  plain-text version labels in INSTALL.md, README.md, PYPI_README.md,
  docs/GPU_AND_CUPY.md, docs/SERVICE_API_SCHEMA.md, examples/*.py.
- CHANGELOG.md / RELEASE_NOTES.md: add matching 0.6.0 entries.

Author: qectorlab

CHANGELOG.md

@@ -7,6 +7,30 @@ environment so report figures trace back to a specific build.
 
 ## [Unreleased]
 
+## [0.6.0] - 2026-07-05
+
+### Fixed
+- **README.md / PYPI_README.md**: the Stim detector-error-model workflow
+  example referenced `qector_decoder_v3.stim_compat.stim_circuit_to_check_matrix`,
+  a function that does not exist (it was superseded by
+  `from_stim_detector_error_model` during the 0.5.9 cleanup, without the
+  docs being updated). Both quick-start examples now import
+  `from_stim_detector_error_model` and build the `check_to_qubits` mapping
+  from a real `stim.DetectorErrorModel` (`circuit.detector_error_model(...)`),
+  matching the documented function's actual signature.
+- **Python 3.9 compatibility**: replaced PEP 604 `X | None` union syntax with
+  `typing.Optional`/`typing.Union` in `backend.py`, `qiskit_plugin.py`,
+  `stim_compat.py`, and `__init__.py`. This syntax requires Python 3.10+ and
+  would raise `TypeError` at import time on 3.9, contradicting the package's
+  own `requires-python = ">=3.9"` and the `smoke-import-py3.9` CI job.
+- Hardened `test_clean_venv_install.py`'s qiskit-absent smoke test to also
+  stub out `qiskit`, not just `stim`/`pymatching`.
+- Version-string consistency: bumped `pyproject.toml`, `Cargo.toml`,
+  `Cargo.lock`, `python/qector_decoder_v3/__init__.py`, `CITATION.cff`, and
+  `codemeta.json` to `0.6.0`, and updated all plain-text version labels in
+  `INSTALL.md`, `README.md`, `PYPI_README.md`, `docs/GPU_AND_CUPY.md`,
+  `docs/SERVICE_API_SCHEMA.md`, and the `examples/` scripts.
+
 ## [0.5.9] - 2026-07-02
 
 ### Added

CITATION.cff

@@ -6,8 +6,8 @@ authors:
   - family-names: Lessard
     given-names: Guillaume
     affiliation: iD01t Productions
-version: 0.5.9
-date-released: 2026-07-02
+version: 0.6.0
+date-released: 2026-07-05
 url: https://www.qector.store
 repository-code: https://github.com/GuillaumeLessard/qector-decoder
 identifiers:

Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "qector_decoder_v3"
-version = "0.5.9"
+version = "0.6.0"
 edition = "2021"
 authors = ["Guillaume Lessard / iD01t Productions <guiliguili2705@gmail.com>"]
 description = "Source-available Rust QEC decoder core (Union-Find, exact polynomial MWPM/Blossom, Sparse Blossom, BP-OSD) with CPU/CUDA/OpenCL batch decoding and PyO3 bindings"

Cargo.toml

@@ -1,4 +1,4 @@
-# Installation Guide - QECTOR Decoder v0.5.9
+# Installation Guide - QECTOR Decoder v0.6.0
 
 The current repository does **not** include `install.py`. Use the source build path below.
 
@@ -24,7 +24,7 @@ $env:PYO3_PYTHON = (Resolve-Path .\.venv\Scripts\python.exe).Path
 This command has been verified from a fresh clone on a second Windows PC with Python 3.11. The expected successful ending is:
 
 ```text
-Installed qector-decoder-v3-0.5.9
+Installed qector-decoder-v3-0.6.0
 QECTOR OK
 ```
 

INSTALL.md

@@ -78,7 +78,7 @@ Stim workflow:
 ```python
 import stim
 from qector_decoder_v3 import BlossomDecoder
-from qector_decoder_v3.stim_compat import stim_circuit_to_check_matrix
+from qector_decoder_v3.stim_compat import from_stim_detector_error_model
 
 circuit = stim.Circuit.generated(
     "surface_code:rotated_memory_z",
@@ -87,7 +87,8 @@ circuit = stim.Circuit.generated(
     after_clifford_depolarization=0.005,
 )
 
-checks, n_qubits = stim_circuit_to_check_matrix(circuit)
+dem = circuit.detector_error_model(decompose_errors=True)
+checks, n_qubits = from_stim_detector_error_model(dem)
 decoder = BlossomDecoder(checks, n_qubits)
 ```
 
@@ -173,7 +174,7 @@ admin@qector.store
   author  = {Guillaume Lessard},
   title   = {{QECTOR Decoder v3}: Rust/Python Quantum Error Correction Decoding Platform},
   year    = {2026},
-  version = {0.5.9},
+  version = {0.6.0},
   url     = {https://www.qector.store},
   note    = {Source-available. Commercial license required for commercial use.}
 }

PYPI_README.md

@@ -106,7 +106,7 @@ if CUDABatchDecoder.is_available():
 ```python
 import stim
 from qector_decoder_v3 import BlossomDecoder
-from qector_decoder_v3.stim_compat import stim_circuit_to_check_matrix
+from qector_decoder_v3.stim_compat import from_stim_detector_error_model
 
 circuit = stim.Circuit.generated(
     "surface_code:rotated_memory_z",
@@ -115,7 +115,8 @@ circuit = stim.Circuit.generated(
     after_clifford_depolarization=0.005,
 )
 
-checks, n_qubits = stim_circuit_to_check_matrix(circuit)
+dem = circuit.detector_error_model(decompose_errors=True)
+checks, n_qubits = from_stim_detector_error_model(dem)
 decoder = BlossomDecoder(checks, n_qubits)
 ```
 
@@ -173,7 +174,7 @@ See [`docs/API_STABILITY.md`](docs/API_STABILITY.md) before building production
 
 ## Validated evidence snapshot
 
-All public claims should cite an artifact, commit, command, machine, and version. The current package release is **v0.5.9**; checked-in evidence should be regenerated before making new performance claims.
+All public claims should cite an artifact, commit, command, machine, and version. The current package release is **v0.6.0**; checked-in evidence should be regenerated before making new performance claims.
 
 ### MWPM parity against PyMatching
 
@@ -400,7 +401,7 @@ See [`COMMERCIAL.md`](COMMERCIAL.md) and [`LICENSE`](LICENSE) for full terms.
   author  = {Guillaume Lessard},
   title   = {{QECTOR Decoder v3}: Rust/Python Quantum Error Correction Decoding Platform},
   year    = {2026},
-  version = {0.5.9},
+  version = {0.6.0},
   url     = {https://www.qector.store},
   note    = {Source-available. Commercial license required for commercial use.}
 }

README.md

@@ -1,3 +1,24 @@
+# QECTOR Decoder v0.6.0 - Release Notes
+
+**Version**: 0.6.0
+**Date**: 2026-07-05
+
+This release fixes documented API drift in `README.md` and `PYPI_README.md`:
+the Stim detector-error-model quick-start referenced
+`stim_compat.stim_circuit_to_check_matrix`, a function removed during the
+`0.5.9` cleanup and superseded by `from_stim_detector_error_model`. Both
+examples now use the real function against a `stim.DetectorErrorModel`. This
+release also fixes genuine Python 3.9 incompatibilities: PEP 604 `X | None`
+union syntax (3.10+ only) in `backend.py`, `qiskit_plugin.py`,
+`stim_compat.py`, and `__init__.py` is replaced with
+`typing.Optional`/`typing.Union`, matching the package's stated
+`requires-python = ">=3.9"` and its `smoke-import-py3.9` CI job. Package
+metadata (`pyproject.toml`, `Cargo.toml`, `Cargo.lock`, runtime fallback
+version, `CITATION.cff`, `codemeta.json`) and all plain-text version labels
+across docs and `examples/` are bumped to `0.6.0`.
+
+---
+
 # QECTOR Decoder v0.5.9 - Release Notes
 
 **Version**: 0.5.9

RELEASE_NOTES.md

@@ -1 +1 @@
-{"@context":"https://doi.org/10.5063/schema/codemeta-2.0","@type":"SoftwareSourceCode","name":"QECTOR Decoder v3","version":"0.5.9","description":"Source-available Rust and Python quantum error correction decoder package for QEC research, PyMatching-compatible validation, belief-matching, BP-OSD and qLDPC workflows, CPU/GPU batch decoding, and reproducible benchmark evidence.","codeRepository":"https://github.com/GuillaumeLessard/qector-decoder","url":"https://www.qector.store","downloadUrl":"https://pypi.org/project/qector-decoder-v3/","identifier":"https://doi.org/10.5281/zenodo.20825980","license":"https://www.qector.store/license.html","programmingLanguage":["Python","Rust"],"runtimePlatform":["CPython 3.9","CPython 3.10","CPython 3.11","CPython 3.12","CPython 3.13","Linux x86_64","Windows x64","macOS arm64"],"keywords":["quantum error correction","QEC","quantum computing","quantum decoder","MWPM","PyMatching","Stim","Sinter","LDPC","qLDPC","BP-OSD","belief matching","union find decoder","surface code","Rust","Python","PyO3","maturin","QECTOR"],"author":{"@type":"Person","givenName":"Guillaume","familyName":"Lessard","affiliation":"iD01t Productions"},"publisher":{"@type":"Organization","name":"iD01t Productions"}}
+{"@context":"https://doi.org/10.5063/schema/codemeta-2.0","@type":"SoftwareSourceCode","name":"QECTOR Decoder v3","version":"0.6.0","description":"Source-available Rust and Python quantum error correction decoder package for QEC research, PyMatching-compatible validation, belief-matching, BP-OSD and qLDPC workflows, CPU/GPU batch decoding, and reproducible benchmark evidence.","codeRepository":"https://github.com/GuillaumeLessard/qector-decoder","url":"https://www.qector.store","downloadUrl":"https://pypi.org/project/qector-decoder-v3/","identifier":"https://doi.org/10.5281/zenodo.20825980","license":"https://www.qector.store/license.html","programmingLanguage":["Python","Rust"],"runtimePlatform":["CPython 3.9","CPython 3.10","CPython 3.11","CPython 3.12","CPython 3.13","Linux x86_64","Windows x64","macOS arm64"],"keywords":["quantum error correction","QEC","quantum computing","quantum decoder","MWPM","PyMatching","Stim","Sinter","LDPC","qLDPC","BP-OSD","belief matching","union find decoder","surface code","Rust","Python","PyO3","maturin","QECTOR"],"author":{"@type":"Person","givenName":"Guillaume","familyName":"Lessard","affiliation":"iD01t Productions"},"publisher":{"@type":"Organization","name":"iD01t Productions"}}

codemeta.json

@@ -1,6 +1,6 @@
 # GPU & CuPy Acceleration
 
-**QECTOR Decoder v3 — v0.5.9**
+**QECTOR Decoder v3 — v0.6.0**
 
 This document describes the **hybrid GPU acceleration strategy** in QECTOR
 Decoder v3: a Rust native-CUDA batch hot path plus an optional CuPy backend for