diff --git a/internal/common/task_utils.go b/internal/common/task_utils.go
index b89a8d5..1542912 100644
--- a/internal/common/task_utils.go
+++ b/internal/common/task_utils.go
@@ -58,6 +58,13 @@ func AugmentArgsForTask(task *types.Task, args []string, opts TaskAugmentOptions
 				args = append(args, "--no-computer-use")
 			}
 		}
+
+		// Pass harness setting if explicitly configured.
+		if task.AgentConfigSnapshot.Harness != nil && task.AgentConfigSnapshot.Harness.Type != nil {
+			if harness := strings.TrimSpace(*task.AgentConfigSnapshot.Harness.Type); harness != "" {
+				args = append(args, "--harness", harness)
+			}
+		}
 	}
 
 	if task.AgentConfigSnapshot != nil && task.AgentConfigSnapshot.EnvironmentID != nil {
diff --git a/internal/common/task_utils_test.go b/internal/common/task_utils_test.go
index 3348a66..1e47bef 100644
--- a/internal/common/task_utils_test.go
+++ b/internal/common/task_utils_test.go
@@ -55,6 +55,26 @@ func TestAugmentArgsForTask_IdleOnCompletePrecedence(t *testing.T) {
 			opts:     TaskAugmentOptions{IdleOnComplete: "20m"},
 			expected: []string{"agent", "run", "--idle-on-complete", "20m"},
 		},
+		{
+			name: "adds --harness when harness type is set",
+			task: &types.Task{
+				AgentConfigSnapshot: &types.AmbientAgentConfig{
+					Harness: &types.Harness{Type: strPtr("claude")},
+				},
+			},
+			opts:     TaskAugmentOptions{},
+			expected: []string{"agent", "run", "--harness", "claude", "--idle-on-complete"},
+		},
+		{
+			name: "skips --harness when harness type is nil",
+			task: &types.Task{
+				AgentConfigSnapshot: &types.AmbientAgentConfig{
+					Harness: &types.Harness{},
+				},
+			},
+			opts:     TaskAugmentOptions{},
+			expected: []string{"agent", "run", "--idle-on-complete"},
+		},
 		{
 			name: "still appends other config-derived args before idle timeout",
 			task: &types.Task{
diff --git a/internal/types/messages.go b/internal/types/messages.go
index e11aa9d..3763e05 100644
--- a/internal/types/messages.go
+++ b/internal/types/messages.go
@@ -65,7 +65,20 @@ type TaskDefinition struct {
 	Prompt string `json:"prompt"`
 }
 
-// AmbientAgentConfig represents the agent configuration
+// Harness defines a third-party harness to run a cloud agent with.
+type Harness struct {
+	// Type is the name of the harness, e.g. "claude".
+	Type *string `json:"type,omitempty"`
+}
+
+// HarnessAuthSecrets holds authentication secrets for third-party harnesses.
+// Only the secret for the harness specified gets injected into the environment.
+type HarnessAuthSecrets struct {
+	// ClaudeAuthSecretName is the name of a managed secret for Claude Code harness authentication.
+	ClaudeAuthSecretName *string `json:"claude_auth_secret_name,omitempty"`
+}
+
+// AmbientAgentConfig represents the agent configuration.
 type AmbientAgentConfig struct {
 	EnvironmentID      *string                    `json:"environment_id,omitempty"`
 	BasePrompt         *string                    `json:"base_prompt,omitempty"`
@@ -75,6 +88,8 @@ type AmbientAgentConfig struct {
 	MCPServers         map[string]json.RawMessage `json:"mcp_servers,omitempty"`
 	ComputerUseEnabled *bool                      `json:"computer_use_enabled,omitempty"`
 	IdleTimeoutMinutes *int                       `json:"idle_timeout_minutes,omitempty"`
+	Harness            *Harness                   `json:"harness,omitempty"`
+	HarnessAuthSecrets *HarnessAuthSecrets        `json:"harness_auth_secrets,omitempty"`
 }
 
 // Task represents an ambient agent job.