Fix stream compatibility and vision model exposure

internal/httpapi/admin/rawsamples/handler_raw_samples.go

@@ -15,6 +15,7 @@ import (
 	"ds2api/internal/devcapture"
 	adminshared "ds2api/internal/httpapi/admin/shared"
 	"ds2api/internal/rawsample"
+	"ds2api/internal/util"
 )
 
 type captureChain struct {
@@ -479,10 +480,13 @@ func previewCaptureChainResponse(chain captureChain) string {
 
 func previewText(text string, limit int) string {
 	text = strings.TrimSpace(text)
-	if limit <= 0 || len(text) <= limit {
+	if limit <= 0 {
 		return text
 	}
-	return text[:limit] + "..."
+	if truncated, ok := util.TruncateRunes(text, limit); ok {
+		return truncated + "..."
+	}
+	return text
 }
 
 func captureChainHasTruncatedResponse(chain captureChain) bool {

internal/httpapi/admin/rawsamples/handler_raw_samples_test.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
+	"unicode/utf8"
 
 	"ds2api/internal/devcapture"
 )
@@ -231,6 +232,16 @@ func TestCombineCaptureBodiesPreservesOrderAndSeparators(t *testing.T) {
 	}
 }
 
+func TestPreviewTextPreservesUTF8MB4Characters(t *testing.T) {
+	preview := previewText(strings.Repeat("😀", 281), 280)
+	if !utf8.ValidString(preview) {
+		t.Fatalf("expected valid utf-8 preview, got %q", preview)
+	}
+	if preview != strings.Repeat("😀", 280)+"..." {
+		t.Fatalf("unexpected preview: %q", preview)
+	}
+}
+
 func TestQueryRawSampleCapturesGroupsBySessionAndMatchesQuestion(t *testing.T) {
 	devcapture.Global().Clear()
 	defer devcapture.Global().Clear()