Fallback composer installs to source in CI

.github/workflows/tests.yml

@@ -166,17 +166,28 @@ jobs:
       - name: Resolve dependencies
         run: |
           set -euo pipefail
-          for attempt in 1 2 3; do
-            if docker compose -f docker-compose.yml -f .github/docker-compose.ci.yml exec -T php1 sh -lc "cd /var/www/html && composer install --no-interaction --prefer-dist --no-progress"; then
-              exit 0
-            fi
-            if [ "$attempt" -eq 3 ]; then
-              exit 1
-            fi
-            sleep_seconds=$((attempt * 5))
-            echo "composer install failed; retrying in ${sleep_seconds}s (attempt $((attempt + 1))/3)" >&2
-            sleep "$sleep_seconds"
-          done
+          composer_install() {
+            install_mode="$1"
+            max_attempts="$2"
+            attempt=1
+            while :; do
+              if docker compose -f docker-compose.yml -f .github/docker-compose.ci.yml exec -T php1 sh -lc "cd /var/www/html && composer install --no-interaction ${install_mode} --no-progress"; then
+                return 0
+              fi
+              if [ "$attempt" -ge "$max_attempts" ]; then
+                return 1
+              fi
+              sleep_seconds=$((attempt * 5))
+              echo "composer install ${install_mode} failed; retrying in ${sleep_seconds}s (attempt $((attempt + 1))/${max_attempts})" >&2
+              sleep "$sleep_seconds"
+              attempt=$((attempt + 1))
+            done
+          }
+
+          composer_install --prefer-dist 3 || {
+            echo "Composer dist install failed; retrying with --prefer-source." >&2
+            composer_install --prefer-source 2
+          }
 
       - name: Verify edge gateway test files
         run: >