Add debug step to diagnose Gitea build failure

.gitea/workflows/build.yml

@@ -9,7 +9,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     env:
-      CONVERGE_HASKELL_TOOLS_IMAGE: ghcr.io/flipstone/haskell-tools:debian-ghc-9.10.3-5d6640d
+      IMAGE: ghcr.io/flipstone/haskell-tools:debian-ghc-9.10.3-5d6640d
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -21,10 +21,24 @@ jobs:
           key: stack-${{ runner.os }}-${{ hashFiles('stack.yaml', 'package.yaml', 'converge.cabal') }}
           restore-keys: stack-${{ runner.os }}-
 
-      - name: Build
+      - name: Debug mount
         run: |
           mkdir -p .stack-root build
-          ./hs stack build --copy-bins --local-bin-path /work/build
+          docker run --rm \
+            -v "$(pwd):/work" \
+            -w /work \
+            "$IMAGE" \
+            sh -c 'pwd && ls -la && cat stack.yaml && ls /stack-root'
+
+      - name: Build
+        run: |
+          docker run --rm \
+            -v "$(pwd):/work" \
+            -v "$(pwd)/.stack-root:/stack-root" \
+            -e STACK_ROOT=/stack-root \
+            -w /work \
+            "$IMAGE" \
+            stack build --copy-bins --local-bin-path /work/build
 
       - name: Compress with UPX
         run: |