feat: Add automatic protoc installation to Makefile

Implements automatic protoc download and installation similar to the
main stackrox repo, eliminating the need for manual protoc installation.

Changes:
- Add protoc auto-download logic to Makefile with OS/arch detection
- Downloads protoc 32.1 from GitHub releases to .proto/ directory
- Update proto-generate target to depend on local protoc installation
- Update generate-proto-descriptors.sh to use PROTOC_BIN env var
- Add .proto/ to .gitignore
- Add .proto/ cleanup to clean target

Benefits:
- Developers no longer need to manually install protoc
- Consistent protoc version across all developers and CI
- Works offline after first download

Usage:
  make proto-install   # Install protoc (automatic on proto-generate)
  make proto-generate  # Generate descriptors (auto-installs protoc)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: janisz

.gitignore

@@ -17,6 +17,9 @@
 # Lint output
 /report.xml
 
+# Proto tools
+/.proto/
+
 # E2E tests
 /e2e-tests/.env
 /e2e-tests/mcp-reports/

Makefile

@@ -91,13 +91,52 @@ lint: ## Run golangci-lint
 	go install -v "github.com/golangci/golangci-lint/v2/cmd/golangci-lint@v2.6"
 	golangci-lint run
 
+##############
+## Protobuf ##
+##############
+
+# Protoc version and paths
+PROTOC_VERSION := 32.1
+UNAME_S := $(shell uname -s)
+ifeq ($(UNAME_S),Linux)
+PROTOC_OS = linux
+endif
+ifeq ($(UNAME_S),Darwin)
+PROTOC_OS = osx
+endif
+PROTOC_ARCH=$(shell case $$(uname -m) in (arm64|aarch64) echo aarch_64 ;; (s390x) echo s390_64 ;; (*) uname -m ;; esac)
+
+PROTO_PRIVATE_DIR := .proto
+PROTOC_DIR := $(PROTO_PRIVATE_DIR)/protoc-$(PROTOC_OS)-$(PROTOC_ARCH)-$(PROTOC_VERSION)
+PROTOC := $(PROTOC_DIR)/bin/protoc
+PROTOC_ZIP := protoc-$(PROTOC_VERSION)-$(PROTOC_OS)-$(PROTOC_ARCH).zip
+PROTOC_DOWNLOADS_DIR := $(PROTO_PRIVATE_DIR)/.downloads
+PROTOC_FILE := $(PROTOC_DOWNLOADS_DIR)/$(PROTOC_ZIP)
+
+$(PROTOC_DOWNLOADS_DIR):
+	@mkdir -p "$@"
+
+$(PROTOC_FILE): $(PROTOC_DOWNLOADS_DIR)
+	@echo "Downloading protoc $(PROTOC_VERSION)..."
+	@curl -fSL -o "$@" "https://github.com/protocolbuffers/protobuf/releases/download/v$(PROTOC_VERSION)/$(PROTOC_ZIP)"
+
+$(PROTOC): $(PROTOC_FILE)
+	@echo "Installing protoc to $(PROTOC_DIR)..."
+	@mkdir -p "$(PROTOC_DIR)"
+	@unzip -q -o -d "$(PROTOC_DIR)" "$(PROTOC_FILE)"
+	@test -x "$@"
+	@echo "✓ protoc $(PROTOC_VERSION) installed"
+
+.PHONY: proto-install
+proto-install: $(PROTOC) ## Install protoc locally
+
 .PHONY: proto-setup
 proto-setup: ## Setup proto files from go mod cache
 	@./scripts/setup-proto-files.sh
 
 .PHONY: proto-generate
-proto-generate: ## Generate proto descriptors for WireMock
-	@./scripts/generate-proto-descriptors.sh
+proto-generate: $(PROTOC) ## Generate proto descriptors for WireMock
+	@PROTOC_BIN=$(PROTOC) ./scripts/generate-proto-descriptors.sh
 
 .PHONY: proto-clean
 proto-clean: ## Clean generated proto files
@@ -154,3 +193,4 @@ clean: ## Clean build artifacts and coverage files
 	rm -f $(BINARY_NAME)
 	rm -f $(COVERAGE_OUT)
 	rm -f $(LINT_OUT)
+	rm -rf $(PROTO_PRIVATE_DIR)

scripts/generate-proto-descriptors.sh

@@ -14,15 +14,19 @@ if [ ! -d "$ROX_PROTO_PATH" ]; then
     ./scripts/setup-proto-files.sh
 fi
 
-if ! command -v protoc &> /dev/null; then
+# Use PROTOC_BIN if set (from Makefile), otherwise use system protoc
+PROTOC_CMD="${PROTOC_BIN:-protoc}"
+
+if ! command -v "$PROTOC_CMD" &> /dev/null; then
     echo "Error: protoc is not installed"
-    echo "Install from: https://grpc.io/docs/protoc-installation/"
+    echo "Install with: make proto-install"
+    echo "Or install manually from: https://grpc.io/docs/protoc-installation/"
     exit 1
 fi
 
-echo "Generating proto descriptors..."
+echo "Generating proto descriptors with $PROTOC_CMD..."
 
-protoc \
+"$PROTOC_CMD" \
   --descriptor_set_out="$DESCRIPTOR_DIR/stackrox.dsc" \
   --include_imports \
   --proto_path="$ROX_PROTO_PATH" \