diff --git a/.forgejo/workflows/ci.yml b/.forgejo/workflows/ci.yml
index 5a58da1..9f900c7 100644
--- a/.forgejo/workflows/ci.yml
+++ b/.forgejo/workflows/ci.yml
@@ -37,6 +37,18 @@ jobs:
       - name: Prepare environment
         run: cp .env.testing .env
 
+      # Temporary: MySQL is unreachable at db:3306 under the prebuilt image,
+      # though the identical service block worked on catthehacker/ubuntu.
+      - name: Diagnose service networking
+        continue-on-error: true
+        run: |
+          echo "--- /etc/hosts ---";       cat /etc/hosts || true
+          echo "--- /etc/resolv.conf ---"; cat /etc/resolv.conf || true
+          echo "--- php resolves db ---";  php -r 'var_dump(gethostbyname("db"));' || true
+          echo "--- php connect ---";      php -r '$e=null;$f=@fsockopen("db",3306,$n,$e,3);echo $f?"open\n":"fail: $e\n";' || true
+          echo "--- hostname/ip ---";      hostname -i 2>/dev/null || true
+          echo "--- env ---";              env | sort | grep -iE "host|service|port" || true
+
       - name: Wait for MySQL
         run: |
           for i in $(seq 1 30); do