test: add integration tests with real Consul instance

Add comprehensive integration test suite that runs against a real Consul
instance via Docker Compose. This validates the full election lifecycle
including session management, leader failover, and tag promotion.

Changes:
- Add configs/integration/docker-compose.yaml with minimal Consul setup
- Add internal/ballot/ballot_integration_test.go with 6 integration tests
- Update CI workflow to run integration tests with Consul service container
- Add Makefile with test targets (test, test-integration, etc.)
- Fix releaseSession() to always clear local state even if Destroy fails

Integration tests cover:
- Full election cycle (session, lock, tag promotion)
- Leader failover when session is destroyed
- Tag promotion/demotion
- Health check failure triggers demotion
- Multiple instances competing for leadership
- Session renewal over time

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: ncode

.github/workflows/ci.yml

@@ -20,3 +20,21 @@ jobs:
           verbose: true
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+
+  integration:
+    runs-on: ubuntu-latest
+    services:
+      consul:
+        image: hashicorp/consul:latest
+        ports:
+          - 8500:8500
+        options: --health-cmd="consul members" --health-interval=2s --health-timeout=5s --health-retries=10
+    steps:
+      - uses: actions/[email protected]
+      - uses: actions/[email protected]
+        with:
+          go-version: '1.25'
+      - name: Run integration tests
+        run: go env -w GOTOOLCHAIN=go1.25.0+auto && go test -v -tags=integration -race ./...
+        env:
+          CONSUL_HTTP_ADDR: http://localhost:8500

Makefile

@@ -0,0 +1,28 @@
+.PHONY: build test test-race test-coverage test-integration integration-up integration-down clean
+
+build:
+	go build -v ./...
+
+test:
+	go test -v ./...
+
+test-race:
+	go test -v -race ./...
+
+test-coverage:
+	go test -coverpkg=./... ./... -race -coverprofile=coverage.out -covermode=atomic
+	go tool cover -html=coverage.out -o coverage.html
+
+test-integration: integration-up
+	CONSUL_HTTP_ADDR=http://localhost:8500 go test -v -tags=integration -race ./...
+	$(MAKE) integration-down
+
+integration-up:
+	docker compose -f configs/integration/docker-compose.yaml up -d --wait
+
+integration-down:
+	docker compose -f configs/integration/docker-compose.yaml down -v
+
+clean:
+	rm -f coverage.out coverage.html
+	go clean -testcache

configs/integration/docker-compose.yaml

@@ -0,0 +1,12 @@
+services:
+  consul:
+    image: hashicorp/consul:latest
+    container_name: consul-integration
+    command: "agent -dev -bind=0.0.0.0 -client=0.0.0.0"
+    ports:
+      - "8500:8500"
+    healthcheck:
+      test: ["CMD", "consul", "members"]
+      interval: 2s
+      timeout: 5s
+      retries: 10

internal/ballot/ballot.go

@@ -767,10 +767,10 @@ func (b *Ballot) releaseSession() error {
 		return nil
 	}
 	sessionID := *sessionIDPtr
-	_, err := b.client.Session().Destroy(sessionID, nil)
-	if err != nil {
-		return err
-	}
+	// Always clear the local session state, even if Destroy fails.
+	// The session may have already been invalidated by Consul (e.g., due to
+	// health check failure), but we should still clear our local state.
 	b.sessionID.Store((*string)(nil))
-	return nil
+	_, err := b.client.Session().Destroy(sessionID, nil)
+	return err
 }