diff --git a/internal/adapter/openai/handler_toolcall_test.go b/internal/adapter/openai/handler_toolcall_test.go
index cf2420e..2027729 100644
--- a/internal/adapter/openai/handler_toolcall_test.go
+++ b/internal/adapter/openai/handler_toolcall_test.go
@@ -759,16 +759,18 @@ func TestHandleStreamMultiToolCallDoesNotMergeNamesOrArguments(t *testing.T) {
 	foundSearch := false
 	foundEval := false
 	foundIndex1 := false
-	maxToolCallsInDelta := 0
+	toolCallsDeltaLens := make([]int, 0, 2)
 	for _, frame := range frames {
 		choices, _ := frame["choices"].([]any)
 		for _, item := range choices {
 			choice, _ := item.(map[string]any)
 			delta, _ := choice["delta"].(map[string]any)
-			toolCalls, _ := delta["tool_calls"].([]any)
-			if len(toolCalls) > maxToolCallsInDelta {
-				maxToolCallsInDelta = len(toolCalls)
+			rawToolCalls, hasToolCalls := delta["tool_calls"]
+			if !hasToolCalls {
+				continue
 			}
+			toolCalls, _ := rawToolCalls.([]any)
+			toolCallsDeltaLens = append(toolCallsDeltaLens, len(toolCalls))
 			for _, tc := range toolCalls {
 				tcm, _ := tc.(map[string]any)
 				if idx, ok := tcm["index"].(float64); ok && int(idx) == 1 {
@@ -793,8 +795,8 @@ func TestHandleStreamMultiToolCallDoesNotMergeNamesOrArguments(t *testing.T) {
 	if !foundSearch || !foundEval {
 		t.Fatalf("expected both tool names in stream deltas, foundSearch=%v foundEval=%v body=%s", foundSearch, foundEval, rec.Body.String())
 	}
-	if maxToolCallsInDelta != 2 {
-		t.Fatalf("expected one tool_calls delta containing exactly two calls, max=%d body=%s", maxToolCallsInDelta, rec.Body.String())
+	if len(toolCallsDeltaLens) != 1 || toolCallsDeltaLens[0] != 2 {
+		t.Fatalf("expected exactly one tool_calls delta with two calls, got lens=%v body=%s", toolCallsDeltaLens, rec.Body.String())
 	}
 	if !foundIndex1 {
 		t.Fatalf("expected second tool call index in stream deltas, body=%s", rec.Body.String())
diff --git a/internal/adapter/openai/trace_test.go b/internal/adapter/openai/trace_test.go
new file mode 100644
index 0000000..cbacbf3
--- /dev/null
+++ b/internal/adapter/openai/trace_test.go
@@ -0,0 +1,47 @@
+package openai
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5/middleware"
+)
+
+func traceIDViaMiddleware(req *http.Request) string {
+	if req == nil {
+		return requestTraceID(nil)
+	}
+	var got string
+	h := middleware.RequestID(http.HandlerFunc(func(_ http.ResponseWriter, r *http.Request) {
+		got = requestTraceID(r)
+	}))
+	h.ServeHTTP(httptest.NewRecorder(), req)
+	return got
+}
+
+func TestRequestTraceIDPriority(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/v1/chat/completions?__trace_id=query-trace", nil)
+	req.Header.Set("X-Ds2-Test-Trace", "header-trace")
+	got := traceIDViaMiddleware(req)
+	if got != "query-trace" {
+		t.Fatalf("expected query trace id to win, got %q", got)
+	}
+}
+
+func TestRequestTraceIDHeaderFallback(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/v1/chat/completions", nil)
+	req.Header.Set("X-Ds2-Test-Trace", "header-trace")
+	got := traceIDViaMiddleware(req)
+	if got != "header-trace" {
+		t.Fatalf("expected header trace id to win when query missing, got %q", got)
+	}
+}
+
+func TestRequestTraceIDReqIDFallback(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/v1/chat/completions", nil)
+	got := traceIDViaMiddleware(req)
+	if got == "" {
+		t.Fatal("expected middleware request id fallback to be non-empty")
+	}
+}