chore(build): uv tooling, a Python 3.11 floor, and verified model downloads (epic #701, phases 2.5 & 5) (#713)

* chore(build): migrate justfile tooling to uv

All recipes now run through 'uv run' against .venv, with a shared
DEV_EXTRAS variable (dev + vad) because uv syncs the environment
exactly and would otherwise uninstall the dev tools between
recipes. 'deps' installs dev+vad; new 'deps-all' covers every
extra. 'build' switches to 'uv build'; 'version' uses --no-sync.

Bump [tool.uv] required-version to >=0.12,<0.13 for uv 0.12.x, and
raise the mypy python_version target to 3.12: mypy 1.19 in the lock
cannot target 3.9 and numpy 2.x stubs need a 3.12 target to parse
(mypy is not run in CI or pre-commit; this only affects 'just
typecheck').

* fix(tests): isolate test runs from real XDG state; fix Arch model-path crash

Local test runs failed en masse (185 failures) while CI stayed
green: tests picked up the developer's real ~/.local/share/vocalinux
models via the default XDG paths and switched IBus/keyboard code
paths through the desktop session env (XDG_CURRENT_DESKTOP/
XDG_SESSION_TYPE on GNOME/Wayland, issue #478 branches). conftest
now points XDG base dirs at a throwaway session-wide directory and
clears session variables at import time, mirroring a fresh CI
runner (paths like MODELS_DIR freeze at first import during
collection, so fixture-time isolation is too late).

Also guard the Arch branch of _get_system_model_paths(): it removed
/usr/local/share/vocalinux/models unconditionally and crashed with
ValueError on Arch hosts when a custom XDG_DATA_DIRS never added
that path. Add regression tests, and make the lock-file test assert
the actual $XDG_DATA_HOME/vocalinux contract instead of the
hardcoded ~/.local/share default.

* fix(tests): keep the IBus engine double a plain class

Python 3.14's unittest.mock re-instantiates a user subclass when it builds
child mocks (klass(name=...)). VocalinuxEngine inherits from whatever
IBus.Engine resolves to, and the test module bound that to the MagicMock
class itself, so every engine instantiation raised

    TypeError: VocalinuxEngine.__init__() got an unexpected keyword argument 'name'

on 3.14 while passing on 3.13. Replace it with a plain stand-in class that
still hands out per-instance MagicMocks for the IBus API surface the engine
touches.

The same pattern remains in test_ibus_engine.py, test_ibus_engine_utils.py,
test_ibus_active_engine_guard.py and test_ibus_xkb_wayland.py; those never
instantiate the engine, so they are unaffected for now.

* fix(install): build the venv from the system Python

install.sh looked up a bare `python3` from PATH. Started from an activated
virtualenv — a shell left in uv's .venv after `just deps` — it built venv/
from that interpreter, where distro PyGObject is invisible even with
--system-site-packages, and the run aborted with

    Distro PyGObject (python3-gi / python3-gobject) is not importable in the venv.

A mismatched venv/ then survived every retry, because the installer reuses
whatever venv it finds.

- drop an inherited VIRTUAL_ENV (and its bin from PATH) before any
  interpreter lookup
- select the interpreter explicitly: $SYSTEM_PYTHON (default
  /usr/bin/python3) or PATH python3, preferring one that can import gi,
  and create the venv with it instead of `python3`
- recreate venv/ when it was built by a different interpreter
- name the interpreter in the PyGObject guard's error

Documents the two environments (uv's .venv for tooling, venv/ for the
installed app) in CONTRIBUTING, the justfile header and AGENTS.md, and adds
the mismatch symptom to the INSTALL troubleshooting section.

* chore(python): raise the supported floor to 3.11

requires-python promised 3.9 while the CI matrix ran 3.9/3.10/3.11/3.13,
the classifiers advertised up to 3.14, mypy targeted 3.12 and install.sh
enforced 3.9 — five different answers to "which Python does this support".

Settle on 3.11 everywhere: pyproject (requires-python, classifiers, black
targets), install.sh's MIN_VERSION, check-system-deps.sh, the distro package
map, the CI matrix (now 3.11-3.14, matching the classifiers), the release and
nightly workflows, and the docs.

mypy now targets the floor instead of 3.12, so type checking covers what we
promise; numpy 2.x ships stubs in 3.12 syntax that a 3.11 target cannot
parse, so its imports are skipped. (mypy has 71 pre-existing errors either
way; no CI job gates on it.)

uv.lock and the requirements/* exports are regenerated — dropping 3.9/3.10
removes most of the version-conditional resolution branches.

tests/test_python_version_policy.py pins the invariant: install.sh's floor,
requires-python, the classifiers and the CI matrix must agree.

* ci: run lint and tests from uv.lock

The lock file and the hash-pinned exports were not enforced anywhere: CI
still built a venv by hand and installed unpinned `PyGObject` plus
`-e ".[dev,vad]"`, so the tool versions it checked against had nothing to do
with the ones `just lint` uses locally.

Both Python jobs now use astral-sh/setup-uv and run through `uv sync
--locked` / `uv run --locked`, which also fails the build when uv.lock drifts
from pyproject.toml.

Partially covers phase 5 of #701 (tests install from the lock, lock freshness
gate); trusted publishing, artifact checksums and action SHA pinning are
still open there.

* ci: lint from a dedicated dependency group

The lint job failed on this branch: `uv run --extra dev` syncs the whole
project, so it tried to build pyaudio from source on a runner that installs
no system dependencies.

    src/pyaudio/device_api.c:9:10: fatal error: portaudio.h: No such file or directory

Move black/isort/flake8 out of the `dev` extra into a `lint` dependency
group. CI runs `uv run --locked --only-group lint`, which installs the three
pure-Python tools and skips the project entirely — no portaudio or
girepository headers needed. `just deps` and DEV_EXTRAS request the group
alongside the dev extras, so the local environment still carries test and
lint tooling at once and `just lint` matches CI version for version.

pre-commit is unaffected: its hooks pin their own tool versions upstream.

* fix(install): never configure an engine the venv cannot import

vosk became an optional extra in #705, but the installer still writes
`"engine": "vosk"` into config.json on the whisper.cpp fallback path even
when installing the extra only produced a warning. config.json also survives
reinstalls — every writer guards on "file does not exist" — so an engine
picked by an earlier attempt outlives the venv that supported it. Either way
Vocalinux dies at startup:

    ModuleNotFoundError: No module named 'vosk'

- the fallback now writes the vosk config only when `import vosk` actually
  succeeds, and otherwise leaves the engine configuration alone
- a new verify_configured_engine() runs near the end of the install: if
  config.json selects vosk and the venv cannot import it, it says so and
  prints both fixes instead of leaving a broken install behind

* feat(models): verify every model download against a pinned digest

Pins a sha256/md5 per downloadable speech model in
src/vocalinux/utils/model_checksums.txt and verifies against it in both
install.sh and the runtime downloaders, before the file is moved into place.
Verification fails closed. Covers phase 2.5 of #701; see the PR for details.

* docs(agents): rebase AGENTS.md onto the #727 rewrite

* fix(install): hash models that are already on disk instead of trusting them

* refactor(models): one download path per engine, and fix Whisper's

* docs(install): drop distros that cannot meet the 3.11 floor

* docs: retire the distros and Python versions the 3.11 floor rules out

* fix(install): abort instead of warning when Python is below the floor

* fix(install): fall back to the system Python, not the one on PATH

* fix(install): match an existing venv by installation, not by X.Y

* fix(install): repair a config naming an engine the venv cannot import

* fix(models): pin VOSK by the sha256 of bytes we fetched, not upstream's md5

* fix(justfile): request the dev set in every recipe that syncs

* test(version): scan the docs and website trees for a stale Python floor

* docs: correct the stale model-checksum and distro claims

* fix(models): stamp the VOSK tree the app extracts, as the installer does

* fix(install): replace an unverified VOSK model only once its successor is ready

* docs(install): align the Fedora floor with the rest of the tree

* test(install): drop an f-string with no placeholders

* test(models): stub the downloader probe the VOSK installer test relies on

* docs: drop the long dashes from two model-checksum comments

* fix(install): gate on the interpreter, not on the distro release label

* fix(justfile): export the lint group into requirements/dev.txt

* fix(models): unpack the VOSK tree into staging and stamp it before the swap

* fix(whisper): adopt a checkpoint an earlier release stored under the catalog name

* docs(settings): state what a stray Whisper copy really means for deletion

* fix(models): hash a whisper.cpp model found on disk before it reaches ctypes

* docs(contributing): stop telling readers to uninstall their linters

* fix(install): stop warning off distros the project documents as supported

* docs(distros): file the supported derivatives under supported

tests/test_python_version_policy.py

@@ -0,0 +1,128 @@
+"""Guard against Python-version drift between the places that declare it.
+
+`requires-python`, the classifiers, the CI matrix and install.sh's MIN_VERSION
+used to disagree (3.9 floor, 3.9-3.13 matrix, classifiers promising 3.14), which
+is how an unsupported interpreter can quietly become the one users install with.
+"""
+
+import re
+import sys
+import tomllib
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+PYPROJECT = REPO_ROOT / "pyproject.toml"
+INSTALL_SH = REPO_ROOT / "install.sh"
+PIPELINE = REPO_ROOT / ".github" / "workflows" / "unified-pipeline.yml"
+PKGBUILD = REPO_ROOT / "packaging" / "aur" / "vocalinux" / "PKGBUILD"
+
+# Everything user-facing that could state the floor. Scanned as trees rather than
+# a fixed list: docs and the website drifted to "3.9+" for a full release cycle
+# after the floor moved, and a new page must not be able to reintroduce it.
+DOC_AND_SITE_GLOBS = [
+    (REPO_ROOT / "docs", "**/*.md"),
+    (REPO_ROOT / "web" / "src", "**/*.tsx"),
+    (REPO_ROOT / "web" / "src", "**/*.ts"),
+    (REPO_ROOT, "README.md"),
+    (REPO_ROOT, "CONTRIBUTING.md"),
+]
+
+
+def _doc_and_site_files() -> list:
+    files = []
+    for base, pattern in DOC_AND_SITE_GLOBS:
+        files.extend(p for p in base.glob(pattern) if "node_modules" not in p.parts)
+    return sorted(set(files))
+
+
+def _version_tuple(version: str) -> tuple:
+    return tuple(int(part) for part in version.split("."))
+
+
+def _pyproject() -> dict:
+    with PYPROJECT.open("rb") as handle:
+        return tomllib.load(handle)
+
+
+def _requires_python_floor() -> str:
+    requires = _pyproject()["project"]["requires-python"]
+    match = re.fullmatch(r">=\s*(\d+\.\d+)", requires.strip())
+    assert match, f"unexpected requires-python format: {requires!r}"
+    return match.group(1)
+
+
+def _classifier_versions() -> list:
+    versions = []
+    for classifier in _pyproject()["project"]["classifiers"]:
+        match = re.fullmatch(r"Programming Language :: Python :: (\d+\.\d+)", classifier)
+        if match:
+            versions.append(match.group(1))
+    return versions
+
+
+def _ci_matrix_versions() -> list:
+    match = re.search(r"python-version: \[([^\]]+)\]", PIPELINE.read_text(encoding="utf-8"))
+    assert match, "python-version matrix not found in unified-pipeline.yml"
+    return re.findall(r"'(\d+\.\d+)'", match.group(1))
+
+
+def _install_sh_min_version() -> str:
+    # Anchored on the function: install.sh also carries an Ubuntu MIN_VERSION.
+    match = re.search(
+        r'check_python_version\(\) \{.*?local MIN_VERSION="(\d+\.\d+)"',
+        INSTALL_SH.read_text(encoding="utf-8"),
+        re.DOTALL,
+    )
+    assert match, "check_python_version's MIN_VERSION not found in install.sh"
+    return match.group(1)
+
+
+def test_installer_floor_matches_requires_python():
+    assert _install_sh_min_version() == _requires_python_floor()
+
+
+def test_classifiers_match_supported_range():
+    floor = _requires_python_floor()
+    classifiers = _classifier_versions()
+
+    assert classifiers, "no Programming Language :: Python :: X.Y classifiers"
+    assert min(map(_version_tuple, classifiers)) == _version_tuple(floor)
+
+
+def test_ci_matrix_covers_every_supported_version():
+    # The matrix is the only thing that proves a promised version works.
+    assert sorted(_ci_matrix_versions()) == sorted(_classifier_versions())
+
+
+def test_running_interpreter_is_supported():
+    assert sys.version_info[:2] >= _version_tuple(_requires_python_floor())
+
+
+def _pkgbuild_python_floor() -> str:
+    match = re.search(r"'python>=(\d+\.\d+)'", PKGBUILD.read_text(encoding="utf-8"))
+    assert match, "python>= dependency not found in the AUR PKGBUILD"
+    return match.group(1)
+
+
+def test_aur_package_matches_requires_python():
+    assert _pkgbuild_python_floor() == _requires_python_floor()
+
+
+def test_docs_and_site_do_not_advertise_an_older_floor():
+    """No user-facing file may promise a Python older than the real floor."""
+    floor = _version_tuple(_requires_python_floor())
+    files = _doc_and_site_files()
+    assert files, "found nothing to scan; the docs/website layout moved"
+
+    offenders = []
+    for path in files:
+        text = path.read_text(encoding="utf-8", errors="ignore")
+        for number, line in enumerate(text.splitlines(), 1):
+            for claimed in re.findall(r"Python (\d+\.\d+)\+", line):
+                if _version_tuple(claimed) < floor:
+                    rel = path.relative_to(REPO_ROOT)
+                    offenders.append(f"{rel}:{number} claims Python {claimed}+")
+
+    assert not offenders, "user-facing files promise an unsupported Python:\n" + "\n".join(
+        offenders
+    )