Harden timebox validation and test ForRuntime

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

internal/domain/domain.go

@@ -99,7 +99,7 @@ func NewManual(nextAction, successCondition string, timebox time.Duration) (Comm
 	if successCondition == "" {
 		return Commitment{}, ErrMissingSuccessCondition
 	}
-	if timebox <= 0 {
+	if timebox < time.Second {
 		return Commitment{}, ErrMissingTimebox
 	}
 	return Commitment{

internal/domain/domain_test.go

@@ -53,6 +53,32 @@ func TestNewManualPopulatesDraftCommitment(t *testing.T) {
 	}
 }
 
+func TestNewManualRejectsSubSecondTimebox(t *testing.T) {
+	_, err := NewManual("Refactor state", "tests pass", 500*time.Millisecond)
+	if err != ErrMissingTimebox {
+		t.Fatalf("want ErrMissingTimebox, got %v", err)
+	}
+}
+
+func TestForRuntimePopulatesPolicySnapshot(t *testing.T) {
+	p := ForRuntime("commitment-123", RuntimeActive, EnforcementObserve)
+	if !strings.HasPrefix(p.ID, "policy-") {
+		t.Errorf("id should be prefixed, got %s", p.ID)
+	}
+	if p.CommitmentID != "commitment-123" {
+		t.Errorf("commitment id wrong: %s", p.CommitmentID)
+	}
+	if p.SchemaVersion != PolicySchemaVersion {
+		t.Errorf("schema version wrong: %d", p.SchemaVersion)
+	}
+	if p.RuntimeState != RuntimeActive {
+		t.Errorf("runtime state wrong: %s", p.RuntimeState)
+	}
+	if p.EnforcementLevel != EnforcementObserve {
+		t.Errorf("enforcement level wrong: %s", p.EnforcementLevel)
+	}
+}
+
 func TestCommitmentSerializesSnakeCaseEnums(t *testing.T) {
 	c, _ := NewManual("Port domain", "domain tests pass", 25*time.Minute)
 	data, err := json.Marshal(c)