feat(actions): add go-cache composite action with S3 support

.gitea/actions/go-cache/action.yml

@@ -0,0 +1,83 @@
+name: Go Setup + S3 Caching
+description: Install Go and configure tailscale/go-cache-plugin for Go builds with an S3-compatible backend in Gitea Actions
+author: eric
+
+inputs:
+  go-version:
+    description: Go version to install (e.g., 1.22, 1.24, stable)
+    default: stable
+    required: false
+  cache:
+    description: Enable S3 go-cache-plugin.
+    default: "true"
+    required: false
+  go-cache-plugin-version:
+    description: go-cache-plugin version tag or latest.
+    default: latest
+    required: false
+  s3-bucket:
+    description: S3 bucket for go cache. Leave empty to use local caching only.
+    default: ""
+    required: false
+  s3-endpoint:
+    description: Optional S3-compatible endpoint URL, for example https://s3.example.com.
+    default: ""
+    required: false
+  s3-path-style:
+    description: Enable path-style S3 addressing (useful for MinIO or custom Ceph setups).
+    default: "false"
+    required: false
+  cache-dir:
+    description: Local cache directory for go-cache-plugin before uploading/downloading from S3.
+    default: ~/.cache/go-cache
+    required: false
+
+runs:
+  using: composite
+  steps:
+    - name: Setup Go
+      uses: https://gitea.com/actions/setup-go@v4
+      with:
+        go-version: ${{ inputs.go-version }}
+        # Disable default setup-go local cache if we are using our custom S3 caching
+        cache: ${{ inputs.s3-bucket == '' }}
+
+    - name: Install go-cache-plugin
+      if: ${{ inputs.cache == 'true' && inputs.s3-bucket != '' }}
+      shell: bash
+      run: |
+        echo "Installing go-cache-plugin..."
+        go install github.com/tailscale/go-cache-plugin/cmd/go-cache-plugin@${{ inputs.go-cache-plugin-version }}
+
+    - name: Configure Go Cache
+      if: ${{ inputs.cache == 'true' && inputs.s3-bucket != '' }}
+      shell: bash
+      run: |
+        # Expand cache-dir path
+        CACHE_DIR=$(eval echo "${{ inputs.cache-dir }}")
+        mkdir -p "$CACHE_DIR"
+        
+        # Build GOCACHEPROG command
+        CMD="$HOME/go/bin/go-cache-plugin --cache-dir=$CACHE_DIR --bucket=${{ inputs.s3-bucket }}"
+        
+        if [ -n "${{ inputs.s3-endpoint }}" ]; then
+          CMD="$CMD --s3-endpoint-url=${{ inputs.s3-endpoint }}"
+        fi
+        
+        if [ "${{ inputs.s3-path-style }}" = "true" ]; then
+          CMD="$CMD --s3-path-style=true"
+        fi
+        
+        echo "Configuring GOCACHEPROG: $CMD"
+        echo "GOCACHEPROG=$CMD" >> "$GITHUB_ENV"
+        
+        # Ensure GOEXPERIMENT=cacheprog is enabled for Go 1.21-1.23 compatibility
+        echo "GOEXPERIMENT=cacheprog" >> "$GITHUB_ENV"
+
+        # Align with actions-rust: map SCCACHE secrets to standard AWS variables
+        if [ -n "$SCCACHE_AWS_ACCESS_KEY_ID" ] && [ -z "${AWS_ACCESS_KEY_ID:-}" ]; then
+          echo "AWS_ACCESS_KEY_ID=$SCCACHE_AWS_ACCESS_KEY_ID" >> "$GITHUB_ENV"
+        fi
+        if [ -n "$SCCACHE_AWS_SECRET_ACCESS_KEY" ] && [ -z "${AWS_SECRET_ACCESS_KEY:-}" ]; then
+          echo "AWS_SECRET_ACCESS_KEY=$SCCACHE_AWS_SECRET_ACCESS_KEY" >> "$GITHUB_ENV"
+        fi