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

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

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+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

README.md

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+# actions-go
+
+Reusable Gitea Actions for Go projects.
+
+## actions/go-cache
+
+Composite action that installs Go, installs `tailscale/go-cache-plugin`, and configures Go's native `GOCACHEPROG` to cache Go build and test artifacts in an S3-compatible backend.
+
+This action avoids the need to tar/untar huge build directories manually and leverages standard S3 object storage for fast, reliable caching.
+
+### S3 usage
+
+Create an S3 bucket for your Go build cache, then pass S3 settings as inputs and credentials as normal workflow environment variables or secrets.
+
+For ease of use and compatibility with `actions-rust`, the action automatically maps `SCCACHE_AWS_ACCESS_KEY_ID` and `SCCACHE_AWS_SECRET_ACCESS_KEY` to standard AWS environment variables if they are provided.
+
+```yaml
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Go + S3 Caching
+        uses: https://git.ericxliu.me/eric/actions-go/.gitea/actions/go-cache@main
+        with:
+          go-version: '1.24'
+          s3-bucket: my-go-cache-bucket
+          s3-endpoint: https://s3.example.com
+          s3-path-style: "true"
+        env:
+          SCCACHE_AWS_ACCESS_KEY_ID: ${{ secrets.SCCACHE_AWS_ACCESS_KEY_ID }}
+          SCCACHE_AWS_SECRET_ACCESS_KEY: ${{ secrets.SCCACHE_AWS_SECRET_ACCESS_KEY }}
+          AWS_REGION: auto
+
+      - run: go test -v ./...
+```
+
+### Local usage
+
+Omit `s3-bucket` to fall back to the default `setup-go` action's local caching behavior:
+
+```yaml
+- name: Setup Go (local cache)
+  uses: https://git.ericxliu.me/eric/actions-go/.gitea/actions/go-cache@main
+  with:
+    go-version: '1.24'
+```
+
+### Inputs
+
+- `go-version`: Go version to install. Defaults to `stable`.
+- `cache`: Set to `"false"` to opt-out of all caching setup.
+- `go-cache-plugin-version`: Specific version tag or `latest` of the cache plugin. Defaults to `latest`.
+- `s3-bucket`: S3 bucket name. Empty means local caching only.
+- `s3-endpoint`: Optional S3-compatible endpoint URL (e.g., self-hosted MinIO or Ceph).
+- `s3-path-style`: Set to `"true"` for endpoints requiring path-style addressing (e.g., MinIO).
+- `cache-dir`: Local cache directory for caching. Defaults to `~/.cache/go-cache`.