test(openai): assert xhigh/max reach the request body

Wire-level regression guard for the GetEffort clamp removal: a re-clamp to
high would send "high" on the openai-compatible path. Covers both the legacy
reasoning_effort string and the modern reasoning.effort object.

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

Author: sirozha

llms/openai/reasoning_effort_passthrough_test.go

@@ -0,0 +1,68 @@
+package openai
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/vxcontrol/langchaingo/llms"
+)
+
+// Guards the GetEffort clamp removal at the wire level: xhigh/max must reach the
+// request body, not be downgraded to high (legacy reasoning_effort and modern reasoning.effort).
+func TestReasoningEffortPassthroughToWire(t *testing.T) {
+	t.Parallel()
+
+	const completion = `{"id":"x","object":"chat.completion","created":1,"model":"m",` +
+		`"choices":[{"index":0,"message":{"role":"assistant","content":"ok"},"finish_reason":"stop"}],` +
+		`"usage":{"prompt_tokens":1,"completion_tokens":1,"total_tokens":2}}`
+
+	cases := []struct {
+		name   string
+		effort llms.ReasoningEffort
+		modern bool
+		want   string
+	}{
+		{"legacy xhigh", llms.ReasoningXHigh, false, `"reasoning_effort":"xhigh"`},
+		{"legacy max", llms.ReasoningMax, false, `"reasoning_effort":"max"`},
+		{"modern xhigh", llms.ReasoningXHigh, true, `"effort":"xhigh"`},
+		{"modern max", llms.ReasoningMax, true, `"effort":"max"`},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			var body string
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				b, _ := io.ReadAll(r.Body)
+				body = string(b)
+				w.Header().Set("Content-Type", "application/json")
+				_, _ = io.WriteString(w, completion)
+			}))
+			defer srv.Close()
+
+			opts := []Option{WithBaseURL(srv.URL), WithToken("test"), WithModel("reasoning-model")}
+			if tc.modern {
+				opts = append(opts, WithModernReasoningFormat())
+			}
+			llm, err := New(opts...)
+			if err != nil {
+				t.Fatalf("New() error: %v", err)
+			}
+
+			if _, err := llm.GenerateContent(
+				context.Background(),
+				[]llms.MessageContent{llms.TextParts(llms.ChatMessageTypeHuman, "hi")},
+				llms.WithReasoning(tc.effort, 0),
+			); err != nil {
+				t.Fatalf("GenerateContent() error: %v", err)
+			}
+
+			if !strings.Contains(body, tc.want) {
+				t.Fatalf("wire body missing %s\nbody: %s", tc.want, body)
+			}
+		})
+	}
+}