feat(llm): support OpenAI Responses API via per-provider api_type

internal/session/manager.go

@@ -204,10 +204,18 @@ func (m *Manager) CurrentThinking() string {
 	return m.provider.Thinking
 }
 
+func (m *Manager) CurrentAPIType() string {
+	if m.provider.APIType == "" {
+		return config.APITypeChat
+	}
+	return m.provider.APIType
+}
+
 func (m *Manager) Info() string {
 	var b strings.Builder
 	fmt.Fprintf(&b, "provider: %s\n", m.CurrentProvider())
 	fmt.Fprintf(&b, "model: %s\n", m.CurrentModel())
+	fmt.Fprintf(&b, "api: %s\n", m.CurrentAPIType())
 	fmt.Fprintf(&b, "thinking: %s\n", m.CurrentThinking())
 	fmt.Fprintf(&b, "providers: %s\n", strings.Join(m.providerNames(), ", "))
 	fmt.Fprintf(&b, "models: %s\n", strings.Join(m.provider.Models, ", "))
@@ -223,7 +231,7 @@ func (m *Manager) SetProvider(name string) (string, error) {
 	}
 	m.providerName = name
 	m.provider = provider
-	m.syncAgent(llm.NewOpenAICompatibleClient(provider.BaseURL, provider.APIKey, m.httpClient))
+	m.syncAgent(providerClient(provider, m.httpClient))
 	return "Switched provider.\n" + m.summary(), nil
 }
 
@@ -257,7 +265,14 @@ func (m *Manager) SetThinking(level string) (string, error) {
 }
 
 func (m *Manager) summary() string {
-	return fmt.Sprintf("provider: %s\nmodel: %s\nthinking: %s", m.CurrentProvider(), m.CurrentModel(), m.CurrentThinking())
+	return fmt.Sprintf("provider: %s\nmodel: %s\napi: %s\nthinking: %s", m.CurrentProvider(), m.CurrentModel(), m.CurrentAPIType(), m.CurrentThinking())
+}
+
+func providerClient(provider config.ProviderConfig, httpClient *http.Client) llm.Provider {
+	if provider.APIType == config.APITypeResponses {
+		return llm.NewOpenAIResponsesClient(provider.BaseURL, provider.APIKey, httpClient)
+	}
+	return llm.NewOpenAICompatibleClient(provider.BaseURL, provider.APIKey, httpClient)
 }
 
 func (m *Manager) maxContextTokens() int {

internal/session/manager_test.go

@@ -2,6 +2,8 @@ package session
 
 import (
 	"context"
+	"net/http"
+	"net/http/httptest"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -109,6 +111,64 @@ func TestManagerRejectsUnknownModelAndThinking(t *testing.T) {
 	}
 }
 
+func TestManagerSwitchesToResponsesProvider(t *testing.T) {
+	var hitPath string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		hitPath = r.URL.Path
+		w.Header().Set("Content-Type", "text/event-stream")
+		_, _ = w.Write([]byte(`data: {"type":"response.output_text.delta","item_id":"msg_1","output_index":0,"content_index":0,"delta":"ok"}` + "\n\n"))
+		_, _ = w.Write([]byte(`data: {"type":"response.completed","response":{"id":"resp_1","status":"completed"}}` + "\n\n"))
+	}))
+	defer server.Close()
+
+	cfg := &config.Config{
+		Providers: map[string]config.ProviderConfig{
+			"chat": {
+				Name:    "chat",
+				APIType: config.APITypeChat,
+				BaseURL: "https://chat.example.com",
+				APIKey:  "sk-test",
+				Model:   "model-a",
+				Models:  []string{"model-a"},
+			},
+			"responses": {
+				Name:    "responses",
+				APIType: config.APITypeResponses,
+				BaseURL: server.URL,
+				APIKey:  "sk-test",
+				Model:   "model-b",
+				Models:  []string{"model-b"},
+			},
+		},
+	}
+	assistant := agent.New(agent.Options{Provider: &recordingProvider{}, Model: "model-a"})
+	store, err := NewStore(filepath.Join(t.TempDir(), "sessions"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	manager, err := NewManager(cfg, assistant, server.Client(), store)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := manager.SetProvider("responses"); err != nil {
+		t.Fatal(err)
+	}
+	if manager.CurrentAPIType() != config.APITypeResponses {
+		t.Fatalf("api type = %q", manager.CurrentAPIType())
+	}
+	var out strings.Builder
+	if err := assistant.RunTurn(context.Background(), "hi", &out, nil); err != nil {
+		t.Fatal(err)
+	}
+	if hitPath != "/v1/responses" {
+		t.Fatalf("path = %q, want /v1/responses", hitPath)
+	}
+	if out.String() != "ok" {
+		t.Fatalf("output = %q", out.String())
+	}
+}
+
 func TestManagerExposesModelCommandCandidates(t *testing.T) {
 	manager, _, _ := testManager(t)
 	models := manager.AvailableModels()