ci: robust venv creation; verify cached venv has activate and fallback to local

.forgejo/workflows/ci.yml

@@ -73,15 +73,24 @@ jobs:
             REQ_HASH=$(sha256sum requirements.txt | awk '{print $1}')
             PYVER=$(python3 -c 'import sys;print(".".join(map(str, sys.version_info[:2])))')
             CACHE_VENV="/cache/venv-${REQ_HASH}-py${PYVER}"
-            if [ -d "$CACHE_VENV" ]; then
-              echo "Using cached virtualenv: $CACHE_VENV"
-              ln -s "$CACHE_VENV" .venv
-              USE_CACHE=1
-            else
-              echo "Creating cached virtualenv: $CACHE_VENV"
+            if [ ! -f "$CACHE_VENV/bin/activate" ]; then
+              echo "Preparing cached virtualenv: $CACHE_VENV"
+              rm -rf "$CACHE_VENV" || true
               python3 -m venv "$CACHE_VENV"
-              ln -s "$CACHE_VENV" .venv
             fi
+            ln -sfn "$CACHE_VENV" .venv
+            USE_CACHE=1
+          else
+            # Fallback to local venv
+            python3 -m venv .venv
+          fi
+
+          # If the link didn't produce an activate file, fallback to local venv
+          if [ ! -f .venv/bin/activate ]; then
+            echo "Cached venv missing; creating local .venv"
+            rm -f .venv
+            python3 -m venv .venv
+            USE_CACHE=0
           fi
 
           . .venv/bin/activate