fix(agent): encrypt agent access_token at rest (AES-256-GCM via CryptoSecret)

Closes the last review finding: the AM-issued access_token was stored in plaintext
in agent_deployments. Now sealed with common.SealWithCryptoSecret on write and
unsealed on read — the client still receives the plaintext token (no contract
change), but a DB dump no longer exposes live agent tokens. Legacy/plaintext
values and an unset CryptoSecret degrade gracefully (pass-through). Round-trip test added.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

heicode/controller/agent_template_handlers.go

@@ -20,6 +20,34 @@ import (
 // the subdomain directly over SSE. HM is NOT in the agent conversation path.
 // ─────────────────────────────────────────────────────────────────────────────
 
+// sealAgentToken encrypts the AM-issued access token before it is persisted
+// (AES-256-GCM via CryptoSecret). Falls back to plaintext only if CryptoSecret
+// is unset, so the token is never lost.
+func sealAgentToken(token string) string {
+	if strings.TrimSpace(token) == "" {
+		return ""
+	}
+	sealed, err := common.SealWithCryptoSecret([]byte(token))
+	if err != nil {
+		common.SysLog("WARNING: agent access_token stored unencrypted (CryptoSecret unset?): " + err.Error())
+		return token
+	}
+	return sealed
+}
+
+// unsealAgentToken reverses sealAgentToken. If the stored value is not a sealed
+// blob (legacy plaintext / CryptoSecret unset), it is returned as-is.
+func unsealAgentToken(stored string) string {
+	if strings.TrimSpace(stored) == "" {
+		return ""
+	}
+	plain, err := common.UnsealWithCryptoSecret(stored)
+	if err != nil {
+		return stored
+	}
+	return string(plain)
+}
+
 // templateAgentResponse maps a deployed template-agent record to the client view.
 func templateAgentResponse(row model.AgentDeployment) gin.H {
 	var bindingIDs []int
@@ -30,7 +58,7 @@ func templateAgentResponse(row model.AgentDeployment) gin.H {
 		"agent_id":     row.DeploymentID,
 		"template_id":  row.TemplateID,
 		"subdomain":    row.Subdomain,
-		"access_token": row.AccessToken,
+		"access_token": unsealAgentToken(row.AccessToken),
 		"binding_ids":  bindingIDs,
 		"status":       row.Status,
 		"runtime_id":   row.RuntimeDeploymentID,
@@ -110,7 +138,7 @@ func HeicodeDeployAgent(c *gin.Context) {
 		UserID:              strconv.Itoa(userID),
 		TemplateID:          req.TemplateID,
 		Subdomain:           result.Subdomain,
-		AccessToken:         result.AccessToken,
+		AccessToken:         sealAgentToken(result.AccessToken),
 		BindingIDsJSON:      string(bindingIDsJSON),
 		RuntimeDeploymentID: result.RuntimeID,
 		Status:              firstNonEmpty(result.Status, "running"),

heicode/controller/agent_template_test.go

@@ -8,6 +8,7 @@ import (
 	"sync"
 	"testing"
 
+	"github.com/heicode/manager/common"
 	"github.com/heicode/manager/model"
 	"github.com/stretchr/testify/require"
 )
@@ -197,6 +198,20 @@ func TestSeedAndLoadAgentTemplate(t *testing.T) {
 	require.Equal(t, int64(19), count) // all presets seeded
 }
 
+func TestAgentTokenSealRoundTrip(t *testing.T) {
+	old := common.CryptoSecret
+	common.CryptoSecret = "unit-test-crypto-secret"
+	defer func() { common.CryptoSecret = old }()
+
+	sealed := sealAgentToken("super-secret-agent-token")
+	require.NotEqual(t, "super-secret-agent-token", sealed) // encrypted at rest
+	require.NotEmpty(t, sealed)
+	require.Equal(t, "super-secret-agent-token", unsealAgentToken(sealed)) // recovered
+
+	require.Equal(t, "", sealAgentToken(""))
+	require.Equal(t, "plain-legacy", unsealAgentToken("plain-legacy")) // non-sealed passes through
+}
+
 func TestTemplateAgentResponse(t *testing.T) {
 	row := model.AgentDeployment{
 		DeploymentID:   "dep_abc",