Add libpython3.so to python-android-dart-*.tar.gz

The abi3 stub libpython3.so forwards Limited API symbols to the
version-specific libpython3.X.so. The dart-bridge repo's
libdart_bridge-android-*.so links against this stub (DT_NEEDED
libpython3.so), so it has to be present at runtime alongside the
version-specific libpython that serious_python_android already
ships in the APK's jniLibs.

mobile-forge produces libpython3.so in the install tree
($install_root/android/<abi>/python-<X.Y.Z>/lib/libpython3.so);
package-for-dart.sh just wasn't copying it into the tarball before
nuking $build_dir/lib. Add a single cp alongside the existing
libpython3.X.so copy.

CI gating (temporary, marked TODO in comments):
  - build-{darwin,linux,windows}: skipped on dart-bridge branch so
    the iteration cycle for this Android-only artifact change
    doesn't fan out to slow Darwin/Linux/Windows rebuilds.
  - publish-release: extended to publish from dart-bridge branch too,
    and allows skipped sibling needs (won't cascade-skip if
    build-darwin/linux/windows are gated off). Reverts to
    main-branch-only publish once Android is verified end-to-end.

Author: FeodorFitsner

.github/workflows/build-python-version.yml

@@ -31,6 +31,11 @@ permissions:
 jobs:
   build-darwin:
     name: Build Python for iOS and macOS
+    # TEMPORARY: disabled on dart-bridge branch so the Android-only re-release
+    # (adding libpython3.so to python-android-dart tarball) doesn't fan out to
+    # slow Darwin/Linux/Windows builds. Revert this `if:` once Android is
+    # verified end-to-end.
+    if: github.ref != 'refs/heads/dart-bridge'
     runs-on: macos-26
     steps:
       - name: Checkout
@@ -128,6 +133,7 @@ jobs:
 
   build-linux:
     name: Build Python for Linux
+    if: github.ref != 'refs/heads/dart-bridge'  # see build-darwin note
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -161,6 +167,7 @@ jobs:
 
   build-windows:
     name: Build Python for Windows
+    if: github.ref != 'refs/heads/dart-bridge'  # see build-darwin note
     runs-on: windows-2022
     steps:
       - uses: actions/checkout@v4
@@ -193,14 +200,22 @@ jobs:
   publish-release:
     name: Publish Release Assets
     runs-on: ubuntu-latest
-    # Only publish GitHub release assets from the main branch; other branches still
-    # build (and upload per-job artifacts) but don't touch releases.
-    if: github.ref == 'refs/heads/main'
     needs:
       - build-darwin
       - build-android
       - build-linux
       - build-windows
+    # TEMPORARY: dart-bridge branch publishes an Android-only re-release
+    # (adding libpython3.so to python-android-dart). Once verified end-to-end,
+    # revert this `if:` (and the build-{darwin,linux,windows} `if:` skips) so
+    # `main` is the sole publisher. Allowing the job when sibling `needs:`
+    # are *skipped* — not just *success* — keeps the cascade from blocking us.
+    if: |
+      (github.ref == 'refs/heads/main' || github.ref == 'refs/heads/dart-bridge')
+      && needs.build-android.result == 'success'
+      && (needs.build-darwin.result == 'success' || needs.build-darwin.result == 'skipped')
+      && (needs.build-linux.result == 'success' || needs.build-linux.result == 'skipped')
+      && (needs.build-windows.result == 'success' || needs.build-windows.result == 'skipped')
     permissions:
       contents: write
     steps:

android/package-for-dart.sh

@@ -114,6 +114,11 @@ rm -rf $bundle_dir
 # copy python*.so from lib
 cp $build_dir/lib/libpython$python_version_short.so $build_dir
 
+# abi3 stub libpython3.so — forwards Limited API symbols to the version-
+# specific libpython. Consumed by libdart_bridge (dart-bridge repo), whose
+# DT_NEEDED libpython3.so needs to resolve at runtime on the device.
+cp $build_dir/lib/libpython3.so $build_dir
+
 # copy deps
 for name in crypto ssl sqlite3; do
     cp "$build_dir/lib/lib${name}_"python.so "$build_dir"