ci: point uv at the venv interpreter by path for free-threaded jobs

Activating the venv and passing --active still let 'uv sync' run its own
interpreter discovery, which skips free-threaded builds and re-picked the
system 3.12, recreating .venv and breaking the cp313t/cp314t wheel
install. Pass the venv's own interpreter (.venv/bin/python) explicitly to
'uv sync', 'uv pip install', and 'uv run' so every step stays in the
free-threaded environment created by 'uv venv'.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: timsaucer

.github/workflows/test.yml

@@ -81,20 +81,21 @@ jobs:
       - name: Install from pre-built wheels
         run: |
           set -x
-          # Create the venv with the setup-python interpreter, then activate
-          # it so every uv command targets that same .venv. Using UV_PYTHON
-          # instead diverges: `uv sync` populates .venv while `uv pip install`
-          # targets the bare interpreter, so the datafusion wheel never lands
-          # in .venv. `--active` stops `uv sync` from discovering and
-          # recreating the env with the system 3.12.
+          # Create the venv with the setup-python interpreter, then point
+          # every uv command explicitly at the venv's own interpreter.
+          # uv's interpreter discovery skips free-threaded builds unless
+          # asked by exact path, so plain `uv sync` (even with an activated
+          # venv or --active) re-picks the system 3.12 and recreates .venv.
+          # Targeting .venv/bin/python keeps sync and pip install in the
+          # same 3.13t/3.14t environment as the cp313t/cp314t wheel.
           uv venv --python "${{ steps.setup-python.outputs.python-path }}"
-          source .venv/bin/activate
-          uv sync --active --dev --no-install-package datafusion
+          VENV_PY="$PWD/.venv/bin/python"
+          uv sync --python "$VENV_PY" --dev --no-install-package datafusion
           WHEELS=$(find wheels/ -name "*.whl")
           if [ -n "$WHEELS" ]; then
             echo "Installing wheels:"
             echo "$WHEELS"
-            uv pip install wheels/*.whl
+            uv pip install --python "$VENV_PY" wheels/*.whl
           else
             echo "ERROR: No wheels found!"
             exit 1
@@ -108,7 +109,9 @@ jobs:
           PYTHON_GIL: ${{ matrix.freethreaded && '0' || '' }}
         run: |
           git submodule update --init
-          uv run --no-project pytest -v --import-mode=importlib
+          # Use the .venv interpreter directly; uv discovery would skip the
+          # free-threaded build and re-pick the system 3.12 (see install step).
+          uv run --python "$PWD/.venv/bin/python" --no-project pytest -v --import-mode=importlib
 
       # FFI + TPC-H examples only need to run once; gate to abi3 entries.
       - name: FFI unit tests