diff --git a/.gitea/workflows/ci-debug.yml b/.gitea/workflows/ci-debug.yml
new file mode 100644
index 0000000..3d2e0d4
--- /dev/null
+++ b/.gitea/workflows/ci-debug.yml
@@ -0,0 +1,42 @@
+name: CI debug
+
+on:
+  push:
+    branches: [ci-debug]
+
+env:
+  ZIG_VERSION: "0.16.0"
+
+jobs:
+  probe:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Zig
+        uses: mlugg/setup-zig@v2
+        with:
+          version: ${{ env.ZIG_VERSION }}
+
+      - name: Environment probe
+        run: |
+          echo "HOME=$HOME"
+          env | grep -i zig || true
+          echo "--- global cache candidates ---"
+          for d in "$ZIG_GLOBAL_CACHE_DIR" "$HOME/.cache/zig"; do
+            [ -n "$d" ] && { echo "dir: $d"; ls -la "$d" 2>&1 | head -10; }
+          done
+          echo "--- local cache ---"
+          ls -la .zig-cache 2>&1 | head -10
+
+      - name: Reproduce fetch failure
+        run: |
+          zig build --help >/dev/null 2>&1 || true
+          zig build test 2>&1 | head -5 || true
+
+      - name: Attempt fix (create tmp dirs) and retry fetch
+        run: |
+          for d in "$ZIG_GLOBAL_CACHE_DIR" "$HOME/.cache/zig"; do
+            [ -n "$d" ] && mkdir -p "$d/tmp" "$d/p" && echo "created $d/tmp and $d/p"
+          done
+          zig build test 2>&1 | head -5