Add mTLS to CP→agent channel

- Internal ECDSA P-256 CA (WRENN_CA_CERT/WRENN_CA_KEY env vars); when absent
  the system falls back to plain HTTP so dev mode works without certificates
- Host leaf cert (7-day TTL, IP SAN) issued at registration and renewed on
  every JWT refresh; fingerprint + expiry stored in DB (cert_expires_at column
  replaces the removed mtls_enabled flag)
- CP ephemeral client cert (24-hour TTL) via CPCertStore with atomic hot-swap;
  background goroutine renews it every 12 hours without restarting the server
- Host agent uses tls.Listen + httpServer.Serve so GetCertificate callback is
  respected (ListenAndServeTLS always reads cert from disk)
- Sandbox reverse proxy now uses pool.Transport() so it shares the same TLS
  config as the Connect RPC clients instead of http.DefaultTransport
- Credentials file renamed host-credentials.json with cert_pem/key_pem/
  ca_cert_pem fields; duplicate register/refresh response structs collapsed
  to authResponse

.env.example

@@ -27,6 +27,14 @@ AWS_SECRET_ACCESS_KEY=
 # Auth
 JWT_SECRET=
 
+# mTLS — CP→Agent channel
+# Generate a self-signed CA with:
+#   openssl ecparam -genkey -name P-256 -noout -out ca.key
+#   openssl req -new -x509 -key ca.key -days 3650 -out ca.crt -subj "/CN=wrenn-internal-ca"
+# Then set these to the file contents (newlines replaced with \n or use multiline env).
+WRENN_CA_CERT=-----BEGIN CERTIFICATE-----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\nVM7hllXxL6AdxJtU2vsEoA0=\n-----END CERTIFICATE-----
+WRENN_CA_KEY=-----BEGIN EC PRIVATE KEY-----\nMHcCAQEEIOjpTSFMhhR9Yi2mWtrzJ/FINEImtmz32GkwZ9eYUbDkoAoGCCqGSM49\nAwEHoUQDQgAEOTC/xrVjtfHtrnJQMvANRQGfV9J9SWrqwatWhyJLZlr6+jXfncrr\nUgUw0X0DfC8temwQAZkptrDWIR9GzosRGA==\n-----END EC PRIVATE KEY-----
+
 # OAuth
 OAUTH_GITHUB_CLIENT_ID=
 OAUTH_GITHUB_CLIENT_SECRET=

cmd/control-plane/main.go

@@ -15,6 +15,7 @@ import (
 
 	"git.omukk.dev/wrenn/sandbox/internal/api"
 	"git.omukk.dev/wrenn/sandbox/internal/audit"
+	"git.omukk.dev/wrenn/sandbox/internal/auth"
 	"git.omukk.dev/wrenn/sandbox/internal/auth/oauth"
 	"git.omukk.dev/wrenn/sandbox/internal/config"
 	"git.omukk.dev/wrenn/sandbox/internal/db"
@@ -68,8 +69,52 @@ func main() {
 	}
 	slog.Info("connected to redis")
 
+	// mTLS: parse internal CA and build a TLS-capable host client pool.
+	// When CA env vars are absent the pool falls back to plain HTTP (dev mode).
+	var ca *auth.CA
+	if cfg.CACert != "" && cfg.CAKey != "" {
+		var err error
+		ca, err = auth.ParseCA(cfg.CACert, cfg.CAKey)
+		if err != nil {
+			slog.Error("failed to parse mTLS CA from environment", "error", err)
+			os.Exit(1)
+		}
+		slog.Info("mTLS enabled: CA loaded")
+	} else {
+		slog.Warn("mTLS disabled: WRENN_CA_CERT/WRENN_CA_KEY not set — host agent connections are unencrypted")
+	}
+
 	// Host client pool — manages Connect RPC clients to host agents.
-	hostPool := lifecycle.NewHostClientPool()
+	var hostPool *lifecycle.HostClientPool
+	if ca != nil {
+		cpCertStore, err := auth.NewCPCertStore(ca)
+		if err != nil {
+			slog.Error("failed to issue CP client certificate", "error", err)
+			os.Exit(1)
+		}
+		// Renew the CP client certificate periodically so it never expires
+		// while the control plane is running (TTL = 24h, renewal = every 12h).
+		go func() {
+			ticker := time.NewTicker(auth.CPCertRenewInterval)
+			defer ticker.Stop()
+			for {
+				select {
+				case <-ctx.Done():
+					return
+				case <-ticker.C:
+					if err := cpCertStore.Refresh(); err != nil {
+						slog.Error("failed to renew CP client certificate", "error", err)
+					} else {
+						slog.Info("CP client certificate renewed")
+					}
+				}
+			}
+		}()
+		hostPool = lifecycle.NewHostClientPoolTLS(auth.CPClientTLSConfig(ca, cpCertStore))
+		slog.Info("host client pool: mTLS enabled")
+	} else {
+		hostPool = lifecycle.NewHostClientPool()
+	}
 
 	// Scheduler — picks a host for each new sandbox (round-robin for now).
 	hostScheduler := scheduler.NewRoundRobinScheduler(queries)
@@ -88,7 +133,7 @@ func main() {
 	}
 
 	// API server.
-	srv := api.New(queries, hostPool, hostScheduler, pool, rdb, []byte(cfg.JWTSecret), oauthRegistry, cfg.OAuthRedirectURL)
+	srv := api.New(queries, hostPool, hostScheduler, pool, rdb, []byte(cfg.JWTSecret), oauthRegistry, cfg.OAuthRedirectURL, ca)
 
 	// Start template build workers (2 concurrent).
 	stopBuildWorkers := srv.BuildSvc.StartWorkers(ctx, 2)

cmd/host-agent/main.go

@@ -2,8 +2,10 @@ package main
 
 import (
 	"context"
+	"crypto/tls"
 	"flag"
 	"log/slog"
+	"net"
 	"net/http"
 	"os"
 	"os/signal"
@@ -14,6 +16,7 @@ import (
 
 	"github.com/joho/godotenv"
 
+	"git.omukk.dev/wrenn/sandbox/internal/auth"
 	"git.omukk.dev/wrenn/sandbox/internal/devicemapper"
 	"git.omukk.dev/wrenn/sandbox/internal/hostagent"
 	"git.omukk.dev/wrenn/sandbox/internal/network"
@@ -50,7 +53,7 @@ func main() {
 	listenAddr := envOrDefault("WRENN_HOST_LISTEN_ADDR", ":50051")
 	rootDir := envOrDefault("WRENN_DIR", "/var/lib/wrenn")
 	cpURL := os.Getenv("WRENN_CP_URL")
-	tokenFile := filepath.Join(rootDir, "host.jwt")
+	credsFile := filepath.Join(rootDir, "host-credentials.json")
 
 	if cpURL == "" {
 		slog.Error("WRENN_CP_URL environment variable is required")
@@ -80,10 +83,10 @@ func main() {
 	mgr.StartTTLReaper(ctx)
 
 	// Register with the control plane and start heartbeating.
-	hostToken, err := hostagent.Register(ctx, hostagent.RegistrationConfig{
+	creds, err := hostagent.Register(ctx, hostagent.RegistrationConfig{
 		CPURL:             cpURL,
 		RegistrationToken: *registrationToken,
-		TokenFile:         tokenFile,
+		TokenFile:         credsFile,
 		Address:           *advertiseAddr,
 	})
 	if err != nil {
@@ -91,17 +94,29 @@ func main() {
 		os.Exit(1)
 	}
 
-	hostID, err := hostagent.HostIDFromToken(hostToken)
+	slog.Info("host registered", "host_id", creds.HostID)
-	if err != nil {
-		slog.Error("failed to extract host ID from token", "error", err)
-		os.Exit(1)
-	}
-
-	slog.Info("host registered", "host_id", hostID)
 
 	// httpServer is declared here so the shutdown func can reference it.
 	httpServer := &http.Server{Addr: listenAddr}
 
+	// Set up mTLS if the CP issued a certificate during registration.
+	var certStore hostagent.CertStore
+	if creds.CertPEM != "" && creds.KeyPEM != "" && creds.CACertPEM != "" {
+		if err := certStore.ParseAndStore(creds.CertPEM, creds.KeyPEM); err != nil {
+			slog.Error("failed to load host TLS certificate", "error", err)
+			os.Exit(1)
+		}
+		tlsCfg := auth.AgentTLSConfigFromPEM(creds.CACertPEM, certStore.GetCert)
+		if tlsCfg == nil {
+			slog.Error("failed to build agent TLS config: invalid CA certificate PEM")
+			os.Exit(1)
+		}
+		httpServer.TLSConfig = tlsCfg
+		slog.Info("mTLS enabled on agent server")
+	} else {
+		slog.Warn("mTLS disabled: no certificate received from CP — agent serving plain HTTP")
+	}
+
 	// doShutdown is the single shutdown path. sync.Once ensures mgr.Shutdown
 	// and httpServer.Shutdown are each called exactly once regardless of
 	// whether shutdown is triggered by a signal, a heartbeat 404, or the
@@ -134,7 +149,7 @@ func main() {
 
 	// Start heartbeat loop. Handler must be set before this because the
 	// immediate beat can trigger doShutdown → httpServer.Shutdown synchronously.
-	hostagent.StartHeartbeat(ctx, cpURL, tokenFile, hostID, 30*time.Second,
+	hostagent.StartHeartbeat(ctx, cpURL, credsFile, creds.HostID, 30*time.Second,
 		// pauseAll: called on 3 consecutive network failures.
 		func() {
 			pauseCtx, pauseCancel := context.WithTimeout(context.Background(), 2*time.Minute)
@@ -145,6 +160,17 @@ func main() {
 		func() {
 			doShutdown("host deleted from CP")
 		},
+		// onCredsRefreshed: hot-swap the TLS certificate after a JWT refresh.
+		func(tf *hostagent.TokenFile) {
+			if tf.CertPEM == "" || tf.KeyPEM == "" {
+				return
+			}
+			if err := certStore.ParseAndStore(tf.CertPEM, tf.KeyPEM); err != nil {
+				slog.Error("failed to hot-swap TLS cert after credentials refresh", "error", err)
+			} else {
+				slog.Info("TLS cert hot-swapped after credentials refresh")
+			}
+		},
 	)
 
 	// Graceful shutdown on SIGINT/SIGTERM.
@@ -155,11 +181,31 @@ func main() {
 		doShutdown("signal: " + sig.String())
 	}()
 
-	slog.Info("host agent starting", "addr", listenAddr, "host_id", hostID)
+	slog.Info("host agent starting", "addr", listenAddr, "host_id", creds.HostID)
-	if err := httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+	if httpServer.TLSConfig != nil {
+		// When TLSConfig is pre-populated (cert via GetCertificate callback),
+		// ListenAndServeTLS does not work because it requires on-disk cert/key paths.
+		// Instead, create the TLS listener manually and call Serve.
+		ln, err := tls.Listen("tcp", listenAddr, httpServer.TLSConfig)
+		if err != nil {
+			slog.Error("failed to start TLS listener", "error", err)
+			os.Exit(1)
+		}
+		if err := httpServer.Serve(ln); err != nil && err != http.ErrServerClosed {
+			slog.Error("https server error", "error", err)
+			os.Exit(1)
+		}
+	} else {
+		ln, err := net.Listen("tcp", listenAddr)
+		if err != nil {
+			slog.Error("failed to start listener", "error", err)
+			os.Exit(1)
+		}
+		if err := httpServer.Serve(ln); err != nil && err != http.ErrServerClosed {
 			slog.Error("http server error", "error", err)
 			os.Exit(1)
 		}
+	}
 
 	slog.Info("host agent stopped")
 }

db/migrations/20260330112050_mtls_cert_expiry.sql

@@ -0,0 +1,7 @@
+-- +goose Up
+ALTER TABLE hosts DROP COLUMN mtls_enabled;
+ALTER TABLE hosts ADD COLUMN cert_expires_at TIMESTAMPTZ;
+
+-- +goose Down
+ALTER TABLE hosts DROP COLUMN cert_expires_at;
+ALTER TABLE hosts ADD COLUMN mtls_enabled BOOLEAN NOT NULL DEFAULT FALSE;

db/queries/hosts.sql

@@ -25,11 +25,20 @@ SET arch = $2,
     memory_mb        = $4,
     disk_gb          = $5,
     address          = $6,
+    cert_fingerprint = $7,
+    cert_expires_at  = $8,
     status           = 'online',
     last_heartbeat_at = NOW(),
     updated_at        = NOW()
 WHERE id = $1 AND status = 'pending';
 
+-- name: UpdateHostCert :exec
+UPDATE hosts
+SET cert_fingerprint = $2,
+    cert_expires_at  = $3,
+    updated_at       = NOW()
+WHERE id = $1;
+
 -- name: UpdateHostStatus :exec
 UPDATE hosts SET status = $2, updated_at = NOW() WHERE id = $1;
 

internal/api/handler_sandbox_proxy.go

@@ -42,7 +42,7 @@ func NewSandboxProxyWrapper(inner http.Handler, queries *db.Queries, pool *lifec
 		inner:     inner,
 		db:        queries,
 		pool:      pool,
-		transport: http.DefaultTransport,
+		transport: pool.Transport(),
 	}
 }
 
@@ -110,7 +110,7 @@ func (h *SandboxProxyWrapper) ServeHTTP(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
-	agentAddr := lifecycle.EnsureScheme(agentHost.Address)
+	agentAddr := h.pool.ResolveAddr(agentHost.Address)
 	upstreamPath := fmt.Sprintf("/proxy/%s/%s%s", sandboxIDStr, port, r.URL.Path)
 
 	target, err := url.Parse(agentAddr)

internal/api/handlers_hosts.go

@@ -49,6 +49,9 @@ type refreshTokenResponse struct {
 	Host         hostResponse `json:"host"`
 	Token        string       `json:"token"`
 	RefreshToken string       `json:"refresh_token"`
+	CertPEM      string       `json:"cert_pem,omitempty"`
+	KeyPEM       string       `json:"key_pem,omitempty"`
+	CACertPEM    string       `json:"ca_cert_pem,omitempty"`
 }
 
 type deletePreviewResponse struct {
@@ -69,6 +72,9 @@ type registerHostResponse struct {
 	Host         hostResponse `json:"host"`
 	Token        string       `json:"token"`
 	RefreshToken string       `json:"refresh_token"`
+	CertPEM      string       `json:"cert_pem,omitempty"`
+	KeyPEM       string       `json:"key_pem,omitempty"`
+	CACertPEM    string       `json:"ca_cert_pem,omitempty"`
 }
 
 type addTagRequest struct {
@@ -388,6 +394,9 @@ func (h *hostHandler) Register(w http.ResponseWriter, r *http.Request) {
 		Host:         hostToResponse(result.Host),
 		Token:        result.JWT,
 		RefreshToken: result.RefreshToken,
+		CertPEM:      result.CertPEM,
+		KeyPEM:       result.KeyPEM,
+		CACertPEM:    result.CACertPEM,
 	})
 }
 
@@ -501,6 +510,9 @@ func (h *hostHandler) RefreshToken(w http.ResponseWriter, r *http.Request) {
 		Host:         hostToResponse(result.Host),
 		Token:        result.JWT,
 		RefreshToken: result.RefreshToken,
+		CertPEM:      result.CertPEM,
+		KeyPEM:       result.KeyPEM,
+		CACertPEM:    result.CACertPEM,
 	})
 }
 

internal/api/server.go

@@ -10,6 +10,7 @@ import (
 	"github.com/redis/go-redis/v9"
 
 	"git.omukk.dev/wrenn/sandbox/internal/audit"
+	"git.omukk.dev/wrenn/sandbox/internal/auth"
 	"git.omukk.dev/wrenn/sandbox/internal/auth/oauth"
 	"git.omukk.dev/wrenn/sandbox/internal/db"
 	"git.omukk.dev/wrenn/sandbox/internal/lifecycle"
@@ -36,6 +37,7 @@ func New(
 	jwtSecret []byte,
 	oauthRegistry *oauth.Registry,
 	oauthRedirectURL string,
+	ca *auth.CA,
 ) *Server {
 	r := chi.NewRouter()
 	r.Use(requestLogger())
@@ -44,7 +46,7 @@ func New(
 	sandboxSvc := &service.SandboxService{DB: queries, Pool: pool, Scheduler: sched}
 	apiKeySvc := &service.APIKeyService{DB: queries}
 	templateSvc := &service.TemplateService{DB: queries}
-	hostSvc := &service.HostService{DB: queries, Redis: rdb, JWT: jwtSecret, Pool: pool}
+	hostSvc := &service.HostService{DB: queries, Redis: rdb, JWT: jwtSecret, Pool: pool, CA: ca}
 	teamSvc := &service.TeamService{DB: queries, Pool: pgPool, HostPool: pool}
 	auditSvc := &service.AuditService{DB: queries}
 	statsSvc := &service.StatsService{DB: queries, Pool: pgPool}
@@ -182,6 +184,7 @@ func New(
 		r.Post("/builds", buildH.Create)
 		r.Get("/builds", buildH.List)
 		r.Get("/builds/{id}", buildH.Get)
+		r.Post("/builds/{id}/cancel", buildH.Cancel)
 	})
 
 	return &Server{router: r, BuildSvc: buildSvc}

internal/auth/cert.go

@@ -0,0 +1,251 @@
+package auth
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"fmt"
+	"math/big"
+	"net"
+	"sync/atomic"
+	"time"
+)
+
+// CPCertRenewInterval is how often the control plane should renew its client
+// certificate. It is set to half the cert TTL so there is always a wide safety
+// margin before expiry.
+const CPCertRenewInterval = cpCertTTL / 2
+
+const (
+	hostCertTTL = 7 * 24 * time.Hour
+	cpCertTTL   = 24 * time.Hour
+)
+
+// CA holds a parsed certificate authority ready to issue leaf certificates.
+type CA struct {
+	Cert *x509.Certificate
+	Key  *ecdsa.PrivateKey
+	PEM  string // PEM-encoded certificate for embedding in register/refresh responses
+}
+
+// ParseCA parses PEM-encoded CA certificate and private key strings.
+// The cert and key are expected to be ECDSA P-256.
+func ParseCA(certPEM, keyPEM string) (*CA, error) {
+	certBlock, _ := pem.Decode([]byte(certPEM))
+	if certBlock == nil {
+		return nil, fmt.Errorf("failed to decode CA certificate PEM")
+	}
+	cert, err := x509.ParseCertificate(certBlock.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("parse CA certificate: %w", err)
+	}
+
+	keyBlock, _ := pem.Decode([]byte(keyPEM))
+	if keyBlock == nil {
+		return nil, fmt.Errorf("failed to decode CA key PEM")
+	}
+	keyIface, err := x509.ParseECPrivateKey(keyBlock.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("parse CA private key: %w", err)
+	}
+
+	return &CA{Cert: cert, Key: keyIface, PEM: certPEM}, nil
+}
+
+// HostCert holds all material returned when issuing a leaf cert for a host agent.
+type HostCert struct {
+	CertPEM     string
+	KeyPEM      string
+	Fingerprint string    // hex-encoded SHA-256 of DER bytes, stored in hosts.cert_fingerprint
+	ExpiresAt   time.Time // stored in hosts.cert_expires_at
+	TLSCert     tls.Certificate
+}
+
+// IssueHostCert generates an ECDSA P-256 key pair and issues a 7-day server
+// certificate for the host agent. hostID becomes the common name; the host's
+// IP address (parsed from hostAddr) is added as an IP SAN so Go's TLS
+// stack can verify the connection without disabling hostname checking.
+func IssueHostCert(ca *CA, hostID, hostAddr string) (HostCert, error) {
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return HostCert{}, fmt.Errorf("generate host key: %w", err)
+	}
+
+	serial, err := randomSerial()
+	if err != nil {
+		return HostCert{}, err
+	}
+
+	now := time.Now()
+	expires := now.Add(hostCertTTL)
+
+	tmpl := &x509.Certificate{
+		SerialNumber: serial,
+		Subject:      pkix.Name{CommonName: hostID},
+		NotBefore:    now.Add(-time.Minute), // small clock-skew tolerance
+		NotAfter:     expires,
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+	}
+
+	// Extract IP from "ip:port" address; fall back to DNS SAN if not parseable.
+	host, _, err := net.SplitHostPort(hostAddr)
+	if err != nil {
+		host = hostAddr
+	}
+	if ip := net.ParseIP(host); ip != nil {
+		tmpl.IPAddresses = []net.IP{ip}
+	} else {
+		tmpl.DNSNames = []string{host}
+	}
+
+	derBytes, err := x509.CreateCertificate(rand.Reader, tmpl, ca.Cert, &key.PublicKey, ca.Key)
+	if err != nil {
+		return HostCert{}, fmt.Errorf("create host certificate: %w", err)
+	}
+
+	certPEM := string(pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes}))
+	keyDER, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return HostCert{}, fmt.Errorf("marshal host key: %w", err)
+	}
+	keyPEM := string(pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER}))
+
+	tlsCert, err := tls.X509KeyPair([]byte(certPEM), []byte(keyPEM))
+	if err != nil {
+		return HostCert{}, fmt.Errorf("build TLS certificate: %w", err)
+	}
+
+	fp := fmt.Sprintf("%x", sha256.Sum256(derBytes))
+
+	return HostCert{
+		CertPEM:     certPEM,
+		KeyPEM:      keyPEM,
+		Fingerprint: fp,
+		ExpiresAt:   expires,
+		TLSCert:     tlsCert,
+	}, nil
+}
+
+// IssueCPClientCert generates a short-lived (24h) ECDSA client certificate for
+// the control plane to present during mTLS handshakes with host agents.
+// Called once at CP startup; the result is embedded into the shared HTTP client.
+func IssueCPClientCert(ca *CA) (tls.Certificate, error) {
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("generate CP client key: %w", err)
+	}
+
+	serial, err := randomSerial()
+	if err != nil {
+		return tls.Certificate{}, err
+	}
+
+	now := time.Now()
+	tmpl := &x509.Certificate{
+		SerialNumber: serial,
+		Subject:      pkix.Name{CommonName: "wrenn-cp"},
+		NotBefore:    now.Add(-time.Minute),
+		NotAfter:     now.Add(cpCertTTL),
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
+	}
+
+	derBytes, err := x509.CreateCertificate(rand.Reader, tmpl, ca.Cert, &key.PublicKey, ca.Key)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("create CP client certificate: %w", err)
+	}
+
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
+	keyDER, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("marshal CP client key: %w", err)
+	}
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER})
+
+	return tls.X509KeyPair(certPEM, keyPEM)
+}
+
+// AgentTLSConfigFromPEM returns a tls.Config for the host agent using the
+// PEM-encoded CA certificate. This is used on the agent side where only the
+// CA certificate (not the private key) is available.
+func AgentTLSConfigFromPEM(caCertPEM string, getCert func(*tls.ClientHelloInfo) (*tls.Certificate, error)) *tls.Config {
+	pool := x509.NewCertPool()
+	if !pool.AppendCertsFromPEM([]byte(caCertPEM)) {
+		return nil
+	}
+	return &tls.Config{
+		ClientAuth:     tls.RequireAndVerifyClientCert,
+		ClientCAs:      pool,
+		GetCertificate: getCert,
+		MinVersion:     tls.VersionTLS13,
+	}
+}
+
+// CPCertStore provides lock-free read/write access to the control plane's
+// current client TLS certificate. It is used with tls.Config.GetClientCertificate
+// to enable hot-swap without restarting the HTTP client.
+//
+// The zero value is not usable; use NewCPCertStore to create one.
+type CPCertStore struct {
+	ptr atomic.Pointer[tls.Certificate]
+	ca  *CA
+}
+
+// NewCPCertStore issues an initial CP client certificate from ca and returns a
+// store that can renew it in place. Returns an error if the initial issuance fails.
+func NewCPCertStore(ca *CA) (*CPCertStore, error) {
+	s := &CPCertStore{ca: ca}
+	if err := s.Refresh(); err != nil {
+		return nil, err
+	}
+	return s, nil
+}
+
+// Refresh issues a fresh CP client certificate and atomically stores it.
+// If issuance fails the existing cert is unchanged.
+func (s *CPCertStore) Refresh() error {
+	cert, err := IssueCPClientCert(s.ca)
+	if err != nil {
+		return fmt.Errorf("renew CP client certificate: %w", err)
+	}
+	s.ptr.Store(&cert)
+	return nil
+}
+
+// GetClientCertificate satisfies tls.Config.GetClientCertificate. It is called
+// per-handshake and always returns the most recently stored certificate.
+func (s *CPCertStore) GetClientCertificate(_ *tls.CertificateRequestInfo) (*tls.Certificate, error) {
+	cert := s.ptr.Load()
+	if cert == nil {
+		return nil, fmt.Errorf("no CP client certificate available")
+	}
+	return cert, nil
+}
+
+// CPClientTLSConfig returns a tls.Config for the CP's outbound HTTP client.
+// It uses certStore.GetClientCertificate so the certificate can be renewed
+// without replacing the config or transport.
+func CPClientTLSConfig(ca *CA, certStore *CPCertStore) *tls.Config {
+	pool := x509.NewCertPool()
+	pool.AddCert(ca.Cert)
+	return &tls.Config{
+		RootCAs:               pool,
+		GetClientCertificate:  certStore.GetClientCertificate,
+		MinVersion:            tls.VersionTLS13,
+	}
+}
+
+// randomSerial returns a random 128-bit certificate serial number.
+func randomSerial() (*big.Int, error) {
+	serial, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
+	if err != nil {
+		return nil, fmt.Errorf("generate serial number: %w", err)
+	}
+	return serial, nil
+}

internal/config/config.go

@@ -13,6 +13,11 @@ type Config struct {
 	ListenAddr  string
 	JWTSecret   string
 
+	// mTLS — CP→Agent channel. Both must be set to enable mTLS; omitting either
+	// disables cert issuance and leaves agent connections on plain HTTP (dev mode).
+	CACert string // WRENN_CA_CERT — PEM-encoded internal CA certificate
+	CAKey  string // WRENN_CA_KEY  — PEM-encoded internal CA private key
+
 	OAuthGitHubClientID     string
 	OAuthGitHubClientSecret string
 	OAuthRedirectURL        string
@@ -31,6 +36,9 @@ func Load() Config {
 		ListenAddr:  envOrDefault("WRENN_CP_LISTEN_ADDR", ":8080"),
 		JWTSecret:   os.Getenv("JWT_SECRET"),
 
+		CACert: os.Getenv("WRENN_CA_CERT"),
+		CAKey:  os.Getenv("WRENN_CA_KEY"),
+
 		OAuthGitHubClientID:     os.Getenv("OAUTH_GITHUB_CLIENT_ID"),
 		OAuthGitHubClientSecret: os.Getenv("OAUTH_GITHUB_CLIENT_SECRET"),
 		OAuthRedirectURL:        envOrDefault("OAUTH_REDIRECT_URL", "https://app.wrenn.dev"),

internal/db/hosts.sql.go

@@ -35,7 +35,7 @@ func (q *Queries) DeleteHost(ctx context.Context, id pgtype.UUID) error {
 }
 
 const getHost = `-- name: GetHost :one
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts WHERE id = $1
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts WHERE id = $1
 `
 
 func (q *Queries) GetHost(ctx context.Context, id pgtype.UUID) (Host, error) {
@@ -59,13 +59,13 @@ func (q *Queries) GetHost(ctx context.Context, id pgtype.UUID) (Host, error) {
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.CertFingerprint,
-		&i.MtlsEnabled,
+		&i.CertExpiresAt,
 	)
 	return i, err
 }
 
 const getHostByTeam = `-- name: GetHostByTeam :one
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts WHERE id = $1 AND team_id = $2
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts WHERE id = $1 AND team_id = $2
 `
 
 type GetHostByTeamParams struct {
@@ -94,7 +94,7 @@ func (q *Queries) GetHostByTeam(ctx context.Context, arg GetHostByTeamParams) (H
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.CertFingerprint,
-		&i.MtlsEnabled,
+		&i.CertExpiresAt,
 	)
 	return i, err
 }
@@ -157,7 +157,7 @@ func (q *Queries) GetHostTokensByHost(ctx context.Context, hostID pgtype.UUID) (
 const insertHost = `-- name: InsertHost :one
 INSERT INTO hosts (id, type, team_id, provider, availability_zone, created_by)
 VALUES ($1, $2, $3, $4, $5, $6)
-RETURNING id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled
+RETURNING id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at
 `
 
 type InsertHostParams struct {
@@ -197,7 +197,7 @@ func (q *Queries) InsertHost(ctx context.Context, arg InsertHostParams) (Host, e
 		&i.CreatedAt,
 		&i.UpdatedAt,
 		&i.CertFingerprint,
-		&i.MtlsEnabled,
+		&i.CertExpiresAt,
 	)
 	return i, err
 }
@@ -235,7 +235,7 @@ func (q *Queries) InsertHostToken(ctx context.Context, arg InsertHostTokenParams
 }
 
 const listActiveHosts = `-- name: ListActiveHosts :many
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts WHERE status NOT IN ('pending', 'offline') ORDER BY created_at
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts WHERE status NOT IN ('pending', 'offline') ORDER BY created_at
 `
 
 // Returns all hosts that have completed registration (not pending/offline).
@@ -266,7 +266,7 @@ func (q *Queries) ListActiveHosts(ctx context.Context) ([]Host, error) {
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.CertFingerprint,
-			&i.MtlsEnabled,
+			&i.CertExpiresAt,
 		); err != nil {
 			return nil, err
 		}
@@ -279,7 +279,7 @@ func (q *Queries) ListActiveHosts(ctx context.Context) ([]Host, error) {
 }
 
 const listHosts = `-- name: ListHosts :many
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts ORDER BY created_at DESC
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts ORDER BY created_at DESC
 `
 
 func (q *Queries) ListHosts(ctx context.Context) ([]Host, error) {
@@ -309,7 +309,7 @@ func (q *Queries) ListHosts(ctx context.Context) ([]Host, error) {
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.CertFingerprint,
-			&i.MtlsEnabled,
+			&i.CertExpiresAt,
 		); err != nil {
 			return nil, err
 		}
@@ -322,7 +322,7 @@ func (q *Queries) ListHosts(ctx context.Context) ([]Host, error) {
 }
 
 const listHostsByStatus = `-- name: ListHostsByStatus :many
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts WHERE status = $1 ORDER BY created_at DESC
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts WHERE status = $1 ORDER BY created_at DESC
 `
 
 func (q *Queries) ListHostsByStatus(ctx context.Context, status string) ([]Host, error) {
@@ -352,7 +352,7 @@ func (q *Queries) ListHostsByStatus(ctx context.Context, status string) ([]Host,
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.CertFingerprint,
-			&i.MtlsEnabled,
+			&i.CertExpiresAt,
 		); err != nil {
 			return nil, err
 		}
@@ -365,7 +365,7 @@ func (q *Queries) ListHostsByStatus(ctx context.Context, status string) ([]Host,
 }
 
 const listHostsByTag = `-- name: ListHostsByTag :many
-SELECT h.id, h.type, h.team_id, h.provider, h.availability_zone, h.arch, h.cpu_cores, h.memory_mb, h.disk_gb, h.address, h.status, h.last_heartbeat_at, h.metadata, h.created_by, h.created_at, h.updated_at, h.cert_fingerprint, h.mtls_enabled FROM hosts h
+SELECT h.id, h.type, h.team_id, h.provider, h.availability_zone, h.arch, h.cpu_cores, h.memory_mb, h.disk_gb, h.address, h.status, h.last_heartbeat_at, h.metadata, h.created_by, h.created_at, h.updated_at, h.cert_fingerprint, h.cert_expires_at FROM hosts h
 JOIN host_tags ht ON ht.host_id = h.id
 WHERE ht.tag = $1
 ORDER BY h.created_at DESC
@@ -398,7 +398,7 @@ func (q *Queries) ListHostsByTag(ctx context.Context, tag string) ([]Host, error
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.CertFingerprint,
-			&i.MtlsEnabled,
+			&i.CertExpiresAt,
 		); err != nil {
 			return nil, err
 		}
@@ -411,7 +411,7 @@ func (q *Queries) ListHostsByTag(ctx context.Context, tag string) ([]Host, error
 }
 
 const listHostsByTeam = `-- name: ListHostsByTeam :many
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts WHERE team_id = $1 AND type = 'byoc' ORDER BY created_at DESC
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts WHERE team_id = $1 AND type = 'byoc' ORDER BY created_at DESC
 `
 
 func (q *Queries) ListHostsByTeam(ctx context.Context, teamID pgtype.UUID) ([]Host, error) {
@@ -441,7 +441,7 @@ func (q *Queries) ListHostsByTeam(ctx context.Context, teamID pgtype.UUID) ([]Ho
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.CertFingerprint,
-			&i.MtlsEnabled,
+			&i.CertExpiresAt,
 		); err != nil {
 			return nil, err
 		}
@@ -454,7 +454,7 @@ func (q *Queries) ListHostsByTeam(ctx context.Context, teamID pgtype.UUID) ([]Ho
 }
 
 const listHostsByType = `-- name: ListHostsByType :many
-SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, mtls_enabled FROM hosts WHERE type = $1 ORDER BY created_at DESC
+SELECT id, type, team_id, provider, availability_zone, arch, cpu_cores, memory_mb, disk_gb, address, status, last_heartbeat_at, metadata, created_by, created_at, updated_at, cert_fingerprint, cert_expires_at FROM hosts WHERE type = $1 ORDER BY created_at DESC
 `
 
 func (q *Queries) ListHostsByType(ctx context.Context, type_ string) ([]Host, error) {
@@ -484,7 +484,7 @@ func (q *Queries) ListHostsByType(ctx context.Context, type_ string) ([]Host, er
 			&i.CreatedAt,
 			&i.UpdatedAt,
 			&i.CertFingerprint,
-			&i.MtlsEnabled,
+			&i.CertExpiresAt,
 		); err != nil {
 			return nil, err
 		}
@@ -521,6 +521,8 @@ SET arch = $2,
     memory_mb        = $4,
     disk_gb          = $5,
     address          = $6,
+    cert_fingerprint = $7,
+    cert_expires_at  = $8,
     status           = 'online',
     last_heartbeat_at = NOW(),
     updated_at        = NOW()
@@ -534,6 +536,8 @@ type RegisterHostParams struct {
 	MemoryMb        int32              `json:"memory_mb"`
 	DiskGb          int32              `json:"disk_gb"`
 	Address         string             `json:"address"`
+	CertFingerprint string             `json:"cert_fingerprint"`
+	CertExpiresAt   pgtype.Timestamptz `json:"cert_expires_at"`
 }
 
 func (q *Queries) RegisterHost(ctx context.Context, arg RegisterHostParams) (int64, error) {
@@ -544,6 +548,8 @@ func (q *Queries) RegisterHost(ctx context.Context, arg RegisterHostParams) (int
 		arg.MemoryMb,
 		arg.DiskGb,
 		arg.Address,
+		arg.CertFingerprint,
+		arg.CertExpiresAt,
 	)
 	if err != nil {
 		return 0, err
@@ -565,6 +571,25 @@ func (q *Queries) RemoveHostTag(ctx context.Context, arg RemoveHostTagParams) er
 	return err
 }
 
+const updateHostCert = `-- name: UpdateHostCert :exec
+UPDATE hosts
+SET cert_fingerprint = $2,
+    cert_expires_at  = $3,
+    updated_at       = NOW()
+WHERE id = $1
+`
+
+type UpdateHostCertParams struct {
+	ID              pgtype.UUID        `json:"id"`
+	CertFingerprint string             `json:"cert_fingerprint"`
+	CertExpiresAt   pgtype.Timestamptz `json:"cert_expires_at"`
+}
+
+func (q *Queries) UpdateHostCert(ctx context.Context, arg UpdateHostCertParams) error {
+	_, err := q.db.Exec(ctx, updateHostCert, arg.ID, arg.CertFingerprint, arg.CertExpiresAt)
+	return err
+}
+
 const updateHostHeartbeat = `-- name: UpdateHostHeartbeat :exec
 UPDATE hosts SET last_heartbeat_at = NOW(), updated_at = NOW() WHERE id = $1
 `

internal/db/models.go

@@ -48,7 +48,7 @@ type Host struct {
 	CreatedAt        pgtype.Timestamptz `json:"created_at"`
 	UpdatedAt        pgtype.Timestamptz `json:"updated_at"`
 	CertFingerprint  string             `json:"cert_fingerprint"`
-	MtlsEnabled      bool               `json:"mtls_enabled"`
+	CertExpiresAt    pgtype.Timestamptz `json:"cert_expires_at"`
 }
 
 type HostRefreshToken struct {
@@ -171,6 +171,7 @@ type TemplateBuild struct {
 	CompletedAt  pgtype.Timestamptz `json:"completed_at"`
 	TemplateID   pgtype.UUID        `json:"template_id"`
 	TeamID       pgtype.UUID        `json:"team_id"`
+	SkipPrePost  bool               `json:"skip_pre_post"`
 }
 
 type User struct {

internal/hostagent/certstore.go

@@ -0,0 +1,42 @@
+package hostagent
+
+import (
+	"crypto/tls"
+	"fmt"
+	"sync/atomic"
+)
+
+// CertStore provides lock-free read/write access to the agent's current TLS
+// certificate. It is used with tls.Config.GetCertificate to enable hot-swap
+// of the agent's cert on JWT refresh without restarting the server.
+//
+// The zero value is usable; GetCert returns an error until a cert is stored.
+type CertStore struct {
+	ptr atomic.Pointer[tls.Certificate]
+}
+
+// Store atomically replaces the current certificate.
+func (s *CertStore) Store(cert *tls.Certificate) {
+	s.ptr.Store(cert)
+}
+
+// ParseAndStore parses certPEM+keyPEM and atomically replaces the stored cert.
+// If parsing fails the existing cert is unchanged.
+func (s *CertStore) ParseAndStore(certPEM, keyPEM string) error {
+	cert, err := tls.X509KeyPair([]byte(certPEM), []byte(keyPEM))
+	if err != nil {
+		return fmt.Errorf("parse TLS key pair: %w", err)
+	}
+	s.ptr.Store(&cert)
+	return nil
+}
+
+// GetCert satisfies tls.Config.GetCertificate. Returns an error if no cert has
+// been stored yet.
+func (s *CertStore) GetCert(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
+	cert := s.ptr.Load()
+	if cert == nil {
+		return nil, fmt.Errorf("no TLS certificate available")
+	}
+	return cert, nil
+}

internal/hostagent/registration.go

@@ -17,18 +17,24 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-// tokenFile is the JSON format persisted to WRENN_DIR/host.jwt.
+// TokenFile is the JSON format persisted to WRENN_DIR/host-credentials.json.
-type tokenFile struct {
+// It holds all credentials the agent needs: the host JWT, refresh token, and
+// (when mTLS is enabled) the TLS certificate material for the agent's server.
+type TokenFile struct {
 	HostID       string `json:"host_id"`
 	JWT          string `json:"jwt"`
 	RefreshToken string `json:"refresh_token"`
+	// mTLS fields — empty when the CP has no CA configured.
+	CertPEM   string `json:"cert_pem,omitempty"`
+	KeyPEM    string `json:"key_pem,omitempty"`
+	CACertPEM string `json:"ca_cert_pem,omitempty"`
 }
 
 // RegistrationConfig holds the configuration for host registration.
 type RegistrationConfig struct {
 	CPURL             string // Control plane base URL (e.g., http://localhost:8000)
 	RegistrationToken string // One-time registration token from the control plane
-	TokenFile         string // Path to persist the host JWT after registration
+	TokenFile         string // Path to persist the credentials after registration
 	Address           string // Externally-reachable address (ip:port) for this host
 }
 
@@ -41,22 +47,20 @@ type registerRequest struct {
 	Address  string `json:"address"`
 }
 
-type registerResponse struct {
+// authResponse is the shared JSON shape for both register and refresh responses.
+type authResponse struct {
 	Host         json.RawMessage `json:"host"`
 	Token        string          `json:"token"`
 	RefreshToken string          `json:"refresh_token"`
+	CertPEM      string          `json:"cert_pem,omitempty"`
+	KeyPEM       string          `json:"key_pem,omitempty"`
+	CACertPEM    string          `json:"ca_cert_pem,omitempty"`
 }
 
 type refreshRequest struct {
 	RefreshToken string `json:"refresh_token"`
 }
 
-type refreshResponse struct {
-	Host         json.RawMessage `json:"host"`
-	Token        string          `json:"token"`
-	RefreshToken string          `json:"refresh_token"`
-}
-
 type errorResponse struct {
 	Error struct {
 		Code    string `json:"code"`
@@ -64,8 +68,8 @@ type errorResponse struct {
 	} `json:"error"`
 }
 
-// loadTokenFile reads and parses the persisted token file.
+// LoadTokenFile reads and parses the persisted credentials file.
-func loadTokenFile(path string) (*tokenFile, error) {
+func LoadTokenFile(path string) (*TokenFile, error) {
 	data, err := os.ReadFile(path)
 	if err != nil {
 		return nil, err
@@ -75,36 +79,36 @@ func loadTokenFile(path string) (*tokenFile, error) {
 	if !strings.HasPrefix(trimmed, "{") {
 		// Old format: just the JWT, no refresh token.
 		hostID, _ := hostIDFromJWT(trimmed)
-		return &tokenFile{HostID: hostID, JWT: trimmed}, nil
+		return &TokenFile{HostID: hostID, JWT: trimmed}, nil
 	}
-	var tf tokenFile
+	var tf TokenFile
 	if err := json.Unmarshal(data, &tf); err != nil {
-		return nil, fmt.Errorf("parse token file: %w", err)
+		return nil, fmt.Errorf("parse credentials file: %w", err)
 	}
 	return &tf, nil
 }
 
-// saveTokenFile writes the token file as JSON with 0600 permissions.
+// saveTokenFile writes the credentials file as JSON with 0600 permissions.
-func saveTokenFile(path string, tf tokenFile) error {
+func saveTokenFile(path string, tf TokenFile) error {
 	data, err := json.MarshalIndent(tf, "", "  ")
 	if err != nil {
-		return fmt.Errorf("marshal token file: %w", err)
+		return fmt.Errorf("marshal credentials file: %w", err)
 	}
 	return os.WriteFile(path, data, 0600)
 }
 
 // Register calls the control plane to register this host agent and persists
-// the returned JWT and refresh token to disk. Returns the host JWT token string.
+// the returned credentials to disk. Returns the full TokenFile on success.
-func Register(ctx context.Context, cfg RegistrationConfig) (string, error) {
+func Register(ctx context.Context, cfg RegistrationConfig) (*TokenFile, error) {
-	// If no explicit registration token was given, reuse the saved JWT.
+	// If no explicit registration token was given, reuse the saved credentials.
 	// A --register flag always overrides the local file so operators can
-	// force re-registration without manually deleting host.jwt.
+	// force re-registration without manually deleting the credentials file.
 	if cfg.RegistrationToken == "" {
-		if tf, err := loadTokenFile(cfg.TokenFile); err == nil && tf.JWT != "" {
+		if tf, err := LoadTokenFile(cfg.TokenFile); err == nil && tf.JWT != "" {
-			slog.Info("loaded existing host token", "file", cfg.TokenFile, "host_id", tf.HostID)
+			slog.Info("loaded existing host credentials", "file", cfg.TokenFile, "host_id", tf.HostID)
-			return tf.JWT, nil
+			return tf, nil
 		}
-		return "", fmt.Errorf("no saved host token and no registration token provided (use --register flag)")
+		return nil, fmt.Errorf("no saved host credentials and no registration token provided (use --register flag)")
 	}
 
 	arch := runtime.GOARCH
@@ -123,87 +127,90 @@ func Register(ctx context.Context, cfg RegistrationConfig) (string, error) {
 
 	body, err := json.Marshal(reqBody)
 	if err != nil {
-		return "", fmt.Errorf("marshal registration request: %w", err)
+		return nil, fmt.Errorf("marshal registration request: %w", err)
 	}
 
 	url := strings.TrimRight(cfg.CPURL, "/") + "/v1/hosts/register"
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
 	if err != nil {
-		return "", fmt.Errorf("create registration request: %w", err)
+		return nil, fmt.Errorf("create registration request: %w", err)
 	}
 	req.Header.Set("Content-Type", "application/json")
 
 	client := &http.Client{Timeout: 30 * time.Second}
 	resp, err := client.Do(req)
 	if err != nil {
-		return "", fmt.Errorf("registration request failed: %w", err)
+		return nil, fmt.Errorf("registration request failed: %w", err)
 	}
 	defer resp.Body.Close()
 
 	respBody, err := io.ReadAll(resp.Body)
 	if err != nil {
-		return "", fmt.Errorf("read registration response: %w", err)
+		return nil, fmt.Errorf("read registration response: %w", err)
 	}
 
 	if resp.StatusCode != http.StatusCreated {
 		var errResp errorResponse
 		if err := json.Unmarshal(respBody, &errResp); err == nil {
-			return "", fmt.Errorf("registration failed (%d): %s", resp.StatusCode, errResp.Error.Message)
+			return nil, fmt.Errorf("registration failed (%d): %s", resp.StatusCode, errResp.Error.Message)
 		}
-		return "", fmt.Errorf("registration failed (%d): %s", resp.StatusCode, string(respBody))
+		return nil, fmt.Errorf("registration failed (%d): %s", resp.StatusCode, string(respBody))
 	}
 
-	var regResp registerResponse
+	var regResp authResponse
 	if err := json.Unmarshal(respBody, &regResp); err != nil {
-		return "", fmt.Errorf("parse registration response: %w", err)
+		return nil, fmt.Errorf("parse registration response: %w", err)
 	}
 
 	if regResp.Token == "" {
-		return "", fmt.Errorf("registration response missing token")
+		return nil, fmt.Errorf("registration response missing token")
 	}
 
 	hostID, err := hostIDFromJWT(regResp.Token)
 	if err != nil {
-		return "", fmt.Errorf("extract host ID from JWT: %w", err)
+		return nil, fmt.Errorf("extract host ID from JWT: %w", err)
 	}
 
-	// Persist JWT + refresh token.
+	tf := TokenFile{
-	tf := tokenFile{
 		HostID:       hostID,
 		JWT:          regResp.Token,
 		RefreshToken: regResp.RefreshToken,
+		CertPEM:      regResp.CertPEM,
+		KeyPEM:       regResp.KeyPEM,
+		CACertPEM:    regResp.CACertPEM,
 	}
 	if err := saveTokenFile(cfg.TokenFile, tf); err != nil {
-		return "", fmt.Errorf("save host token: %w", err)
+		return nil, fmt.Errorf("save host credentials: %w", err)
 	}
-	slog.Info("host registered and token saved", "file", cfg.TokenFile, "host_id", hostID)
+	slog.Info("host registered and credentials saved", "file", cfg.TokenFile, "host_id", hostID)
 
-	return regResp.Token, nil
+	return &tf, nil
 }
 
-// RefreshJWT exchanges the refresh token for a new JWT + rotated refresh token.
+// RefreshCredentials exchanges the refresh token for a new JWT, rotated refresh
-// It reads and updates the token file in place.
+// token, and (when mTLS is enabled) a new TLS certificate. The credentials file
-func RefreshJWT(ctx context.Context, cpURL, tokenFilePath string) (string, error) {
+// is updated in place. Returns the updated TokenFile.
-	tf, err := loadTokenFile(tokenFilePath)
+func RefreshCredentials(ctx context.Context, cpURL, credentialsFilePath string) (*TokenFile, error) {
+	tf, err := LoadTokenFile(credentialsFilePath)
 	if err != nil {
-		return "", fmt.Errorf("load token file: %w", err)
+		return nil, fmt.Errorf("load credentials file: %w", err)
 	}
 	if tf.RefreshToken == "" {
-		return "", fmt.Errorf("no refresh token available; host must re-register")
+		return nil, fmt.Errorf("no refresh token available; host must re-register")
 	}
 
 	body, _ := json.Marshal(refreshRequest{RefreshToken: tf.RefreshToken})
 	url := strings.TrimRight(cpURL, "/") + "/v1/hosts/auth/refresh"
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(body))
 	if err != nil {
-		return "", fmt.Errorf("create refresh request: %w", err)
+		return nil, fmt.Errorf("create refresh request: %w", err)
 	}
 	req.Header.Set("Content-Type", "application/json")
 
 	client := &http.Client{Timeout: 15 * time.Second}
 	resp, err := client.Do(req)
 	if err != nil {
-		return "", fmt.Errorf("refresh request failed: %w", err)
+		return nil, fmt.Errorf("refresh request failed: %w", err)
 	}
 	defer resp.Body.Close()
 
@@ -212,39 +219,47 @@ func RefreshJWT(ctx context.Context, cpURL, tokenFilePath string) (string, error
 	if resp.StatusCode != http.StatusOK {
 		var errResp errorResponse
 		if json.Unmarshal(respBody, &errResp) == nil {
-			return "", fmt.Errorf("refresh failed (%d): %s", resp.StatusCode, errResp.Error.Message)
+			return nil, fmt.Errorf("refresh failed (%d): %s", resp.StatusCode, errResp.Error.Message)
 		}
-		return "", fmt.Errorf("refresh failed (%d): %s", resp.StatusCode, string(respBody))
+		return nil, fmt.Errorf("refresh failed (%d): %s", resp.StatusCode, string(respBody))
 	}
 
-	var refResp refreshResponse
+	var refResp authResponse
 	if err := json.Unmarshal(respBody, &refResp); err != nil {
-		return "", fmt.Errorf("parse refresh response: %w", err)
+		return nil, fmt.Errorf("parse refresh response: %w", err)
 	}
 
 	tf.JWT = refResp.Token
 	tf.RefreshToken = refResp.RefreshToken
-	if err := saveTokenFile(tokenFilePath, *tf); err != nil {
+	if refResp.CertPEM != "" {
-		return "", fmt.Errorf("save refreshed token: %w", err)
+		tf.CertPEM = refResp.CertPEM
+		tf.KeyPEM = refResp.KeyPEM
+		tf.CACertPEM = refResp.CACertPEM
+	}
+	if err := saveTokenFile(credentialsFilePath, *tf); err != nil {
+		return nil, fmt.Errorf("save refreshed credentials: %w", err)
 	}
 
-	slog.Info("host JWT refreshed", "host_id", tf.HostID)
+	slog.Info("host credentials refreshed", "host_id", tf.HostID)
-	return refResp.Token, nil
+	return tf, nil
 }
 
 // StartHeartbeat launches a background goroutine that sends periodic heartbeats
 // to the control plane. It runs until the context is cancelled.
 //
-// On 401/403: the heartbeat loop attempts to refresh the JWT. If the refresh
+// On 401/403: the heartbeat loop attempts to refresh credentials. If the refresh
 // also fails (expired refresh token), it calls pauseAll and stops.
 //
 // On repeated network failures (3 consecutive), it calls pauseAll but keeps
 // retrying — the connection may recover and the host should resume heartbeating.
 //
 // onDeleted is called when CP returns 404, meaning this host record was deleted.
-// The token file is removed before calling onDeleted so subsequent starts prompt
+// The credentials file is removed before calling onDeleted so subsequent starts
-// for a new registration token.
+// prompt for a new registration token.
-func StartHeartbeat(ctx context.Context, cpURL, tokenFilePath, hostID string, interval time.Duration, pauseAll func(), onDeleted func()) {
+//
+// onCredsRefreshed is called after a successful credential refresh (JWT + cert).
+// It may be nil. The caller uses it to hot-swap the agent's TLS certificate.
+func StartHeartbeat(ctx context.Context, cpURL, credentialsFilePath, hostID string, interval time.Duration, pauseAll func(), onDeleted func(), onCredsRefreshed func(*TokenFile)) {
 	client := &http.Client{Timeout: 10 * time.Second}
 
 	go func() {
@@ -255,8 +270,8 @@ func StartHeartbeat(ctx context.Context, cpURL, tokenFilePath, hostID string, in
 		pausedDueToFailure := false
 		currentJWT := ""
 
-		// Load the current JWT from disk.
+		// Load the current JWT from the credentials file.
-		if tf, err := loadTokenFile(tokenFilePath); err == nil {
+		if tf, err := LoadTokenFile(credentialsFilePath); err == nil {
 			currentJWT = tf.JWT
 		}
 
@@ -294,10 +309,10 @@ func StartHeartbeat(ctx context.Context, cpURL, tokenFilePath, hostID string, in
 				pausedDueToFailure = false
 
 			case http.StatusUnauthorized, http.StatusForbidden:
-				slog.Warn("heartbeat: JWT rejected — attempting token refresh")
+				slog.Warn("heartbeat: JWT rejected — attempting credentials refresh")
-				newJWT, refreshErr := RefreshJWT(ctx, cpURL, tokenFilePath)
+				newCreds, refreshErr := RefreshCredentials(ctx, cpURL, credentialsFilePath)
 				if refreshErr != nil {
-					slog.Error("heartbeat: JWT refresh failed — pausing all sandboxes; manual re-registration required",
+					slog.Error("heartbeat: credentials refresh failed — pausing all sandboxes; manual re-registration required",
 						"error", refreshErr)
 					if pauseAll != nil && !pausedDueToFailure {
 						pauseAll()
@@ -306,13 +321,16 @@ func StartHeartbeat(ctx context.Context, cpURL, tokenFilePath, hostID string, in
 					// Stop the heartbeat loop — operator must re-register.
 					return true
 				}
-				currentJWT = newJWT
+				currentJWT = newCreds.JWT
-				slog.Info("heartbeat: JWT refreshed successfully")
+				slog.Info("heartbeat: credentials refreshed successfully")
+				if onCredsRefreshed != nil {
+					onCredsRefreshed(newCreds)
+				}
 
 			case http.StatusNotFound:
-				slog.Error("heartbeat: host no longer exists in CP — host was deleted; removing token file and exiting")
+				slog.Error("heartbeat: host no longer exists in CP — host was deleted; removing credentials file and exiting")
-				if err := os.Remove(tokenFilePath); err != nil && !os.IsNotExist(err) {
+				if err := os.Remove(credentialsFilePath); err != nil && !os.IsNotExist(err) {
-					slog.Warn("heartbeat: failed to remove token file", "error", err)
+					slog.Warn("heartbeat: failed to remove credentials file", "error", err)
 				}
 				if onDeleted != nil {
 					onDeleted()
@@ -351,7 +369,7 @@ func HostIDFromToken(token string) (string, error) {
 }
 
 // hostIDFromJWT is the internal implementation used by both HostIDFromToken and
-// the token file loader.
+// the credentials file loader.
 func hostIDFromJWT(token string) (string, error) {
 	parts := strings.Split(token, ".")
 	if len(parts) != 3 {

internal/lifecycle/hostpool.go

@@ -1,6 +1,7 @@
 package lifecycle
 
 import (
+	"crypto/tls"
 	"fmt"
 	"net/http"
 	"strings"
@@ -19,14 +20,33 @@ type HostClientPool struct {
 	mu         sync.RWMutex
 	clients    map[string]hostagentv1connect.HostAgentServiceClient
 	httpClient *http.Client
+	scheme     string // "http://" or "https://"
 }
 
-// NewHostClientPool creates a new pool. The underlying HTTP client uses a
+// NewHostClientPool creates a pool that connects to agents over plain HTTP.
-// 10-minute timeout to support long-running streaming operations.
+// Use NewHostClientPoolTLS when mTLS is required.
 func NewHostClientPool() *HostClientPool {
 	return &HostClientPool{
 		clients:    make(map[string]hostagentv1connect.HostAgentServiceClient),
 		httpClient: &http.Client{Timeout: 10 * time.Minute},
+		scheme:     "http://",
+	}
+}
+
+// NewHostClientPoolTLS creates a pool that connects to agents over mTLS.
+// tlsCfg should already carry the CP client cert and CA trust anchor
+// (use auth.CPClientTLSConfig to construct it).
+func NewHostClientPoolTLS(tlsCfg *tls.Config) *HostClientPool {
+	transport := &http.Transport{
+		TLSClientConfig: tlsCfg,
+	}
+	return &HostClientPool{
+		clients: make(map[string]hostagentv1connect.HostAgentServiceClient),
+		httpClient: &http.Client{
+			Timeout:   10 * time.Minute,
+			Transport: transport,
+		},
+		scheme: "https://",
 	}
 }
 
@@ -46,7 +66,7 @@ func (p *HostClientPool) Get(hostID, address string) hostagentv1connect.HostAgen
 	if c, ok = p.clients[hostID]; ok {
 		return c
 	}
-	c = hostagentv1connect.NewHostAgentServiceClient(p.httpClient, EnsureScheme(address))
+	c = hostagentv1connect.NewHostAgentServiceClient(p.httpClient, p.ensureScheme(address))
 	p.clients[hostID] = c
 	return c
 }
@@ -69,7 +89,34 @@ func (p *HostClientPool) Evict(hostID string) {
 	p.mu.Unlock()
 }
 
+// ensureScheme prepends the pool's configured scheme if the address has none.
+func (p *HostClientPool) ensureScheme(addr string) string {
+	if strings.HasPrefix(addr, "http://") || strings.HasPrefix(addr, "https://") {
+		return addr
+	}
+	return p.scheme + addr
+}
+
+// Transport returns the http.RoundTripper used by this pool. Use this when you
+// need to make raw HTTP requests to agent addresses with the same TLS settings
+// as the pool's Connect RPC clients (e.g., the sandbox reverse proxy).
+func (p *HostClientPool) Transport() http.RoundTripper {
+	if p.httpClient.Transport != nil {
+		return p.httpClient.Transport
+	}
+	return http.DefaultTransport
+}
+
+// ResolveAddr prepends the pool's configured scheme to addr if it has none.
+// Use this when constructing URLs that must use the same transport as the pool
+// (e.g., the sandbox proxy handler). Calling Get/GetForHost internally does
+// the same thing, but ResolveAddr exposes it for callers that only need the URL.
+func (p *HostClientPool) ResolveAddr(addr string) string {
+	return p.ensureScheme(addr)
+}
+
 // EnsureScheme adds "http://" if the address has no scheme.
+// Deprecated: use pool.ResolveAddr which respects the pool's TLS setting.
 func EnsureScheme(addr string) string {
 	if strings.HasPrefix(addr, "http://") || strings.HasPrefix(addr, "https://") {
 		return addr

internal/service/host.go

@@ -27,6 +27,7 @@ type HostService struct {
 	Redis *redis.Client
 	JWT   []byte
 	Pool  *lifecycle.HostClientPool
+	CA    *auth.CA // nil disables mTLS cert issuance (dev/test environments)
 }
 
 // HostCreateParams holds the parameters for creating a host.
@@ -55,18 +56,28 @@ type HostRegisterParams struct {
 	Address  string
 }
 
-// HostRegisterResult holds the registered host, its short-lived JWT, and a long-lived refresh token.
+// HostRegisterResult holds the registered host, its short-lived JWT, a long-lived
+// refresh token, and optionally the host's mTLS certificate material.
 type HostRegisterResult struct {
 	Host         db.Host
 	JWT          string
 	RefreshToken string
+	// mTLS cert material — empty when CA is not configured.
+	CertPEM   string
+	KeyPEM    string
+	CACertPEM string
 }
 
-// HostRefreshResult holds a new JWT and rotated refresh token after a successful refresh.
+// HostRefreshResult holds a new JWT and rotated refresh token after a successful
+// refresh, plus refreshed mTLS certificate material when CA is configured.
 type HostRefreshResult struct {
 	Host         db.Host
 	JWT          string
 	RefreshToken string
+	// mTLS cert material — empty when CA is not configured.
+	CertPEM   string
+	KeyPEM    string
+	CACertPEM string
 }
 
 // HostDeletePreview describes what will be affected by deleting a host.
@@ -268,6 +279,15 @@ func (s *HostService) Register(ctx context.Context, p HostRegisterParams) (HostR
 		return HostRegisterResult{}, fmt.Errorf("sign host token: %w", err)
 	}
 
+	// Issue mTLS certificate if CA is configured.
+	var hc auth.HostCert
+	if s.CA != nil {
+		hc, err = auth.IssueHostCert(s.CA, id.FormatHostID(hostID), p.Address)
+		if err != nil {
+			return HostRegisterResult{}, fmt.Errorf("issue host cert: %w", err)
+		}
+	}
+
 	// Atomically update only if still pending (defense-in-depth against races).
 	rowsAffected, err := s.DB.RegisterHost(ctx, db.RegisterHostParams{
 		ID:              hostID,
@@ -276,6 +296,8 @@ func (s *HostService) Register(ctx context.Context, p HostRegisterParams) (HostR
 		MemoryMb:        p.MemoryMB,
 		DiskGb:          p.DiskGB,
 		Address:         p.Address,
+		CertFingerprint: hc.Fingerprint,
+		CertExpiresAt:   pgtype.Timestamptz{Time: hc.ExpiresAt, Valid: s.CA != nil},
 	})
 	if err != nil {
 		return HostRegisterResult{}, fmt.Errorf("register host: %w", err)
@@ -301,7 +323,13 @@ func (s *HostService) Register(ctx context.Context, p HostRegisterParams) (HostR
 		return HostRegisterResult{}, fmt.Errorf("fetch updated host: %w", err)
 	}
 
-	return HostRegisterResult{Host: host, JWT: hostJWT, RefreshToken: refreshToken}, nil
+	result := HostRegisterResult{Host: host, JWT: hostJWT, RefreshToken: refreshToken}
+	if s.CA != nil {
+		result.CertPEM = hc.CertPEM
+		result.KeyPEM = hc.KeyPEM
+		result.CACertPEM = s.CA.PEM
+	}
+	return result, nil
 }
 
 // Refresh validates a refresh token, rotates it (revokes old, issues new),
@@ -328,6 +356,22 @@ func (s *HostService) Refresh(ctx context.Context, refreshToken string) (HostRef
 		return HostRefreshResult{}, fmt.Errorf("sign host JWT: %w", err)
 	}
 
+	// Renew mTLS certificate if CA is configured.
+	var hc auth.HostCert
+	if s.CA != nil {
+		hc, err = auth.IssueHostCert(s.CA, id.FormatHostID(host.ID), host.Address)
+		if err != nil {
+			return HostRefreshResult{}, fmt.Errorf("renew host cert: %w", err)
+		}
+		if err := s.DB.UpdateHostCert(ctx, db.UpdateHostCertParams{
+			ID:              host.ID,
+			CertFingerprint: hc.Fingerprint,
+			CertExpiresAt:   pgtype.Timestamptz{Time: hc.ExpiresAt, Valid: true},
+		}); err != nil {
+			return HostRefreshResult{}, fmt.Errorf("update host cert: %w", err)
+		}
+	}
+
 	// Issue-then-revoke rotation: insert new token first so a crash between
 	// the two DB calls leaves the host with two valid tokens rather than zero.
 	newRefreshToken, err := s.issueRefreshToken(ctx, host.ID)
@@ -340,7 +384,13 @@ func (s *HostService) Refresh(ctx context.Context, refreshToken string) (HostRef
 		return HostRefreshResult{}, fmt.Errorf("revoke old refresh token: %w", err)
 	}
 
-	return HostRefreshResult{Host: host, JWT: hostJWT, RefreshToken: newRefreshToken}, nil
+	result := HostRefreshResult{Host: host, JWT: hostJWT, RefreshToken: newRefreshToken}
+	if s.CA != nil {
+		result.CertPEM = hc.CertPEM
+		result.KeyPEM = hc.KeyPEM
+		result.CACertPEM = s.CA.PEM
+	}
+	return result, nil
 }
 
 // issueRefreshToken creates a new refresh token record in the DB and returns