feat(store): persist the Swarm cluster id of each agent

The Ledger UI groups Swarm services under their cluster and lists the
cluster's managers, so the master needs to know which cluster an agent
belongs to. RecordHello now stores hello.SwarmClusterID in the new
agents.swarm_cluster_id column.

Claude-Session: https://claude.ai/code/session_01GAZsp3P7Qto6JnhipxWUJQ

internal/master/model/model.go

@@ -27,6 +27,9 @@ type Agent struct {
 	Hostname     string
 	AgentVersion string
 	SwarmManager bool
+	// SwarmClusterID is the Swarm cluster the agent's daemon was in when it last
+	// connected; "" outside a swarm.
+	SwarmClusterID string
 	LastSeenAt     *time.Time
 	RevokedAt      *time.Time
 	CreatedAt      time.Time

internal/master/store/agents.go

@@ -13,11 +13,11 @@ import (
 	"github.com/shcizo/package-updater/internal/protocol"
 )
 
-const agentColumns = `id, name, hostname, agent_version, swarm_manager, last_seen_at, revoked_at, created_at`
+const agentColumns = `id, name, hostname, agent_version, swarm_manager, swarm_cluster_id, last_seen_at, revoked_at, created_at`
 
 func scanAgent(row pgx.Row) (model.Agent, error) {
 	var a model.Agent
-	err := row.Scan(&a.ID, &a.Name, &a.Hostname, &a.AgentVersion, &a.SwarmManager, &a.LastSeenAt, &a.RevokedAt, &a.CreatedAt)
+	err := row.Scan(&a.ID, &a.Name, &a.Hostname, &a.AgentVersion, &a.SwarmManager, &a.SwarmClusterID, &a.LastSeenAt, &a.RevokedAt, &a.CreatedAt)
 	if errors.Is(err, pgx.ErrNoRows) {
 		return model.Agent{}, model.ErrNotFound
 	}
@@ -101,8 +101,8 @@ func (s *Store) RevokeAgent(ctx context.Context, id int64, at time.Time) ([]int6
 // RecordHello stores what the agent reported about itself on connect.
 func (s *Store) RecordHello(ctx context.Context, id int64, h protocol.Hello, at time.Time) error {
 	if _, err := s.pool.Exec(ctx,
-		`UPDATE agents SET hostname = $2, agent_version = $3, swarm_manager = $4, last_seen_at = $5 WHERE id = $1`,
-		id, h.Hostname, h.AgentVersion, h.SwarmManager, at); err != nil {
+		`UPDATE agents SET hostname = $2, agent_version = $3, swarm_manager = $4, swarm_cluster_id = $6, last_seen_at = $5 WHERE id = $1`,
+		id, h.Hostname, h.AgentVersion, h.SwarmManager, at, h.SwarmClusterID); err != nil {
 		return fmt.Errorf("record hello: %w", err)
 	}
 	return nil

internal/master/store/agents_integration_test.go

@@ -80,6 +80,7 @@ func TestAgents_RecordHelloAndMarkSeen(t *testing.T) {
 	assert.Equal(t, "swarm-mgr", agents[0].Hostname)
 	assert.Equal(t, "v1", agents[0].AgentVersion)
 	assert.True(t, agents[0].SwarmManager)
+	assert.Equal(t, "c1", agents[0].SwarmClusterID)
 	require.NotNil(t, agents[0].LastSeenAt)
 	assert.True(t, agents[0].LastSeenAt.Equal(at.Add(time.Minute)))
 }

internal/master/store/migrations/0005_agent_cluster.sql

@@ -0,0 +1 @@
+ALTER TABLE agents ADD COLUMN swarm_cluster_id text NOT NULL DEFAULT '';