Separate wheel and source distribution builds

Add build-sourcedist recipe and fix duplicate source dist bug where
macOS/Windows were building source distributions unnecessarily.

Changes to Justfile:
1. Modified 'build' recipe to only build wheels (python -m build --wheel)
   - Keeps NVX flag which only applies to native wheel compilation
   - Clear separation: build = wheels only
2. Added 'build-sourcedist' recipe to build source dist only
   - No NVX flag (doesn't apply to source distributions)
   - Uses python -m build --sdist
3. build-all continues to work as meta-recipe for all venvs

Changes to wheels.yml:
1. Added 'Build source distribution' step (Linux x86_64 only)
   - Runs after wheel build
   - Calls 'just build-sourcedist'
   - Source dists are platform-independent, only need one

Result:
- Linux: Builds wheels (no NVX) + source dist (once)
- macOS: Builds wheels (with NVX) only
- Windows: Builds wheels (with NVX) only

This fixes the bug where macOS and Windows were creating duplicate source
distributions, causing file conflicts during artifact downloads in release
workflow due to overwrite: false setting.

Author: oberstet

.github/workflows/wheels.yml

@@ -192,6 +192,14 @@ jobs:
           just build-all
         shell: bash
 
+      - name: Build source distribution (Linux x86_64 only)
+        if: matrix.platform == 'linux' && matrix.arch == 'x86_64'
+        run: |
+          # Build source distribution (only once, on Linux x86_64)
+          # Source distributions are platform-independent
+          just build-sourcedist
+        shell: bash
+
       - name: Force file system sync (post-build, pre-validation) - Linux
         if: matrix.platform == 'linux'
         run: |

justfile

@@ -789,7 +789,7 @@ docs-clean:
 # -- Building and Publishing
 # -----------------------------------------------------------------------------
 
-# Build distribution packages (wheels and source tarball)
+# Build wheel only (usage: `just build cpy314`)
 build venv="": (install-build-tools venv)
     #!/usr/bin/env bash
     set -e
@@ -801,9 +801,25 @@ build venv="": (install-build-tools venv)
     fi
     VENV_PATH="{{ VENV_DIR }}/${VENV_NAME}"
     VENV_PYTHON=$(just --quiet _get-venv-python "${VENV_NAME}")
-    echo "==> Building distribution packages..."
-    # Set environment variable for NVX acceleration
-    AUTOBAHN_USE_NVX=1 ${VENV_PYTHON} -m build
+    echo "==> Building wheel package..."
+    # Set environment variable for NVX acceleration (only affects wheels)
+    AUTOBAHN_USE_NVX=1 ${VENV_PYTHON} -m build --wheel
+    ls -la dist/
+
+# Build source distribution only (no wheels, no NVX flag needed)
+build-sourcedist venv="": (install-build-tools venv)
+    #!/usr/bin/env bash
+    set -e
+    VENV_NAME="{{ venv }}"
+    if [ -z "${VENV_NAME}" ]; then
+        echo "==> No venv name specified. Auto-detecting from system Python..."
+        VENV_NAME=$(just --quiet _get-system-venv-name)
+        echo "==> Defaulting to venv: '${VENV_NAME}'"
+    fi
+    VENV_PATH="{{ VENV_DIR }}/${VENV_NAME}"
+    VENV_PYTHON=$(just --quiet _get-venv-python "${VENV_NAME}")
+    echo "==> Building source distribution..."
+    ${VENV_PYTHON} -m build --sdist
     ls -la dist/
 
 # Meta-recipe to run `build` on all environments