Cover the lazy config init and restore the uv cache in CI

get_config() builds its instance on first use, so the branch was covered
only when a worker happened to call it before set_config(). Under xdist that
depends on how cases shard across workers, which varies with the core count:
covered locally, uncovered on the two-core runner. Assert it directly.

setup-uv v4 bundles a cache client the GitHub cache service now rejects with
400, so the uv cache never restored and every wheel was redownloaded. Bump
to v9 across all four workflows (build-docs was already drifting at v5).

setup-python read requires-python (">=3.12") and installed 3.14, which uv
then ignored in favour of .python-version (3.13) and downloaded itself.
Point it at .python-version so the interpreter it installs is the one used.

.github/workflows/build-docs.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: astral-sh/setup-uv@v5
+      - uses: astral-sh/setup-uv@v9
       - run: uv sync --group dev
       - run: uv run zensical build
       - uses: actions/configure-pages@v5

.github/workflows/build-publish-slim.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: astral-sh/setup-uv@v4
+      - uses: astral-sh/setup-uv@v9
         with:
           enable-cache: true
       - name: Set up Python

.github/workflows/build-publish.yml

@@ -12,7 +12,7 @@ jobs:
     if: ${{ github.event_name == 'workflow_dispatch' || github.event.workflow_run.conclusion == 'success' }}
     steps:
       - uses: actions/checkout@v4
-      - uses: astral-sh/setup-uv@v4
+      - uses: astral-sh/setup-uv@v9
         with:
           enable-cache: true
       - name: Set up Python

.github/workflows/test.yml

@@ -11,13 +11,13 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: astral-sh/setup-uv@v4
+      - uses: astral-sh/setup-uv@v9
         with:
           enable-cache: true
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version-file: "pyproject.toml"
+          python-version-file: ".python-version"
       - name: Install dependencies
         run: uv sync --all-extras
       - name: Lint
@@ -52,13 +52,13 @@ jobs:
       HF_TOKEN: ${{ secrets.HF_TOKEN }}
     steps:
       - uses: actions/checkout@v4
-      - uses: astral-sh/setup-uv@v4
+      - uses: astral-sh/setup-uv@v9
         with:
           enable-cache: true
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version-file: "pyproject.toml"
+          python-version-file: ".python-version"
       - name: Install dependencies
         run: uv sync --all-extras
       - name: Cache HuggingFace models

tests/test_config.py

@@ -541,3 +541,19 @@ def test_load_default_config_falls_back_to_builtin_defaults(monkeypatch):
     config = _load_default_config()
 
     assert config.model_dump() == AppConfig().model_dump()
+
+
+def test_get_config_initialises_lazily_then_reuses(monkeypatch):
+    """get_config() builds the instance on first use and caches it.
+
+    Asserted explicitly rather than relying on some test happening to be the
+    first caller in its worker process: under xdist that depends on how cases
+    shard across workers, which varies with the core count.
+    """
+    from haiku.rag import config as config_module
+
+    monkeypatch.setattr(config_module, "_config", None)
+
+    first = config_module.get_config()
+    assert isinstance(first, AppConfig)
+    assert config_module.get_config() is first