diff --git a/docs/internal/sources.md b/docs/internal/sources.md
index 73f43a0..3ed9279 100644
--- a/docs/internal/sources.md
+++ b/docs/internal/sources.md
@@ -151,7 +151,8 @@ control into the rendered prompt. The
 `internal/validate` provides validators backed by an operating-system
 filesystem or an `fs.FS`. Invalid generated content is returned as a validation
 result; inability to load, register, or compile a schema is an operational
-error.
+error. Basic validation checks body emptiness on the byte slice directly
+instead of first making a response-sized string copy.
 
 Every preparation operation creates one operation-local validation plan. None,
 basic, and JSON modes retain the effective output contract without source
diff --git a/internal/validate/standard_validator.go b/internal/validate/standard_validator.go
index f56d15d..d3b5dd8 100644
--- a/internal/validate/standard_validator.go
+++ b/internal/validate/standard_validator.go
@@ -188,7 +188,7 @@ func validateArtifact(ctx context.Context, artifact *domain.Artifact, contract d
 		res.IsValid = true
 		return res, nil
 	case domain.ValidationBasic:
-		empty := strings.TrimSpace(string(artifact.Body)) == ""
+		empty := len(bytes.TrimSpace(artifact.Body)) == 0
 		if err := ctx.Err(); err != nil {
 			return domain.ValidationResult{}, err
 		}
diff --git a/internal/validate/standard_validator_test.go b/internal/validate/standard_validator_test.go
index 2368d0c..b0a88c4 100644
--- a/internal/validate/standard_validator_test.go
+++ b/internal/validate/standard_validator_test.go
@@ -36,32 +36,51 @@ func TestStandardValidatorNoneSkipped(t *testing.T) {
 
 func TestStandardValidatorBasicSuccess(t *testing.T) {
 	v := NewStandardValidator("")
-
-	res, err := v.Validate(context.Background(), &domain.Artifact{Body: []byte("hello")}, domain.OutputContract{
-		ValidationMode: domain.ValidationBasic,
-	})
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-	if res.Status != domain.ValidationPassed || !res.IsValid {
-		t.Fatalf("expected passed/valid, got status=%q valid=%v", res.Status, res.IsValid)
+	for _, tc := range []struct {
+		name string
+		body []byte
+	}{
+		{name: "text", body: []byte("hello")},
+		{name: "invalid UTF-8 byte", body: []byte{0xff}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			res, err := v.Validate(context.Background(), &domain.Artifact{Body: tc.body}, domain.OutputContract{
+				ValidationMode: domain.ValidationBasic,
+			})
+			if err != nil {
+				t.Fatalf("expected no error, got %v", err)
+			}
+			if res.Status != domain.ValidationPassed || !res.IsValid {
+				t.Fatalf("expected passed/valid, got status=%q valid=%v", res.Status, res.IsValid)
+			}
+		})
 	}
 }
 
 func TestStandardValidatorBasicFailureEmpty(t *testing.T) {
 	v := NewStandardValidator("")
-
-	res, err := v.Validate(context.Background(), &domain.Artifact{Body: []byte("  \n\t  ")}, domain.OutputContract{
-		ValidationMode: domain.ValidationBasic,
-	})
-	if err != nil {
-		t.Fatalf("expected no error, got %v", err)
-	}
-	if res.Status != domain.ValidationFailed || res.IsValid {
-		t.Fatalf("expected failed/invalid, got status=%q valid=%v", res.Status, res.IsValid)
-	}
-	if len(res.Errors) == 0 {
-		t.Fatal("expected validation errors")
+	for _, tc := range []struct {
+		name string
+		body []byte
+	}{
+		{name: "empty bytes", body: []byte{}},
+		{name: "ASCII whitespace", body: []byte("  \n\t  ")},
+		{name: "Unicode whitespace", body: []byte("\u2003\u00a0\u3000")},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			res, err := v.Validate(context.Background(), &domain.Artifact{Body: tc.body}, domain.OutputContract{
+				ValidationMode: domain.ValidationBasic,
+			})
+			if err != nil {
+				t.Fatalf("expected no error, got %v", err)
+			}
+			if res.Status != domain.ValidationFailed || res.IsValid {
+				t.Fatalf("expected failed/invalid, got status=%q valid=%v", res.Status, res.IsValid)
+			}
+			if len(res.Errors) == 0 {
+				t.Fatal("expected validation errors")
+			}
+		})
 	}
 }
 
@@ -947,7 +966,8 @@ func BenchmarkBasicValidation(b *testing.B) {
 			}
 
 			b.ReportAllocs()
-			b.SetBytes(int64(len(benchmark.body)))
+			// Nonempty input can be classified from its boundary bytes without
+			// scanning the body, so report latency rather than bytes per second.
 			b.ResetTimer()
 			for range b.N {
 				result, err := validator.Validate(ctx, artifact, contract)