ADFA-2602: Qualify the asset zip URL by toolchain version

Two runs from different toolchains wrote the same R2 key, so the second
silently replaced the first at one stable URL and the Slack links were
indistinguishable -- a tester who downloaded from the earlier message got
8.14.3 assets while believing they had 9.6.1.

Read GRADLE_DISTRIBUTION_VERSION from the checked-out org.adfa.constants
and key the upload as assets/<version>/assets-<arch>.zip, so an 8.14.3 and
a 9.6.1 set can coexist and the URL says which is which. The Slack message
now names the Gradle version alongside the ref.

Claude-Session: https://claude.ai/code/session_017HGpMsUzZ5wxCfMtDZ2HGP

Author: alome007

.github/workflows/generate_assets.yml

@@ -327,6 +327,16 @@ jobs:
             -Dorg.gradle.workers.max=1 \
             -Dorg.gradle.parallel=false
 
+      - name: Read the toolchain version
+        id: toolchain
+        run: |
+          set -euo pipefail
+          CONSTANTS=composite-builds/build-deps-common/constants/src/main/java/org/adfa/constants/constants.kt
+          ver=$(grep 'GRADLE_DISTRIBUTION_VERSION' "$CONSTANTS" | grep -o '"[0-9.]*"' | tr -d '"')
+          [ -n "$ver" ] || { echo "ERROR: could not read GRADLE_DISTRIBUTION_VERSION"; exit 1; }
+          echo "GRADLE_VERSION=$ver" >> $GITHUB_OUTPUT
+          echo "toolchain: gradle $ver"
+
       - name: Verify assets zip
         id: assets_zip
         run: |
@@ -354,22 +364,24 @@ jobs:
           CLOUDFLARE_KEY_ID: ${{ vars.CLOUDFLARE_KEY_ID }}
           CLOUDFLARE_SECRET_ACCESS_KEY: ${{ secrets.CLOUDFLARE_SECRET_ACCESS_KEY }}
           R2_BUCKET: ${{ vars.R2_ASSETS_BUCKET || 'apk-repo' }}
-          R2_KEY_PREFIX: assets/
+          R2_KEY_PREFIX: assets/${{ steps.toolchain.outputs.GRADLE_VERSION }}/
         run: |
           uv run --with boto3 scripts/cloudflare-r2-upload.py "${{ steps.assets_zip.outputs.ASSETS_PATH }}"
-          echo "DOWNLOAD_URL=https://download.appdevforall.org/assets/assets-${{ matrix.arch }}.zip" >> $GITHUB_OUTPUT
+          echo "DOWNLOAD_URL=https://download.appdevforall.org/assets/${{ steps.toolchain.outputs.GRADLE_VERSION }}/assets-${{ matrix.arch }}.zip" >> $GITHUB_OUTPUT
 
       - name: Send Slack notification
         env:
           SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK_URL }}
           ASSET_LABEL: ${{ matrix.label }}
           DOWNLOAD_URL: ${{ steps.r2.outputs.DOWNLOAD_URL }}
           BUILD_REF: ${{ inputs.ref }}
+          GRADLE_VERSION: ${{ steps.toolchain.outputs.GRADLE_VERSION }}
         run: |
           jq -n \
             --arg label "$ASSET_LABEL" \
             --arg url "$DOWNLOAD_URL" \
             --arg ref "$BUILD_REF" \
+            --arg gradle "$GRADLE_VERSION" \
             '{
               blocks: [
                 {
@@ -392,7 +404,7 @@ jobs:
                   elements: [
                     {
                       type: "mrkdwn",
-                      text: "Built from `\($ref)`. Push to `/sdcard/Download/` on the device, then `adb shell touch` it."
+                      text: "Gradle \($gradle), built from `\($ref)`. Push to `/sdcard/Download/` on the device, then `adb shell touch` it."
                     }
                   ]
                 }