feat(auth): enhance plugin scheduler with HasScheduler support and fast-path tests

- Added `pluginSchedulerState` interface with `HasScheduler` method for improved plugin scheduler state checks.
- Updated `Manager.hasPluginScheduler` to handle `HasScheduler` logic.
- Implemented and tested fast-path handling for inactive plugin schedulers, including mixed provider scenarios.
- Expanded unit test coverage to ensure correct behavior in various scheduler states.

internal/pluginhost/scheduler.go

@@ -30,6 +30,10 @@ func (h *Host) PickAuth(ctx context.Context, req pluginapi.SchedulerPickRequest)
 	return resp, true, nil
 }
 
+func (h *Host) HasScheduler() bool {
+	return h.schedulerRecord() != nil
+}
+
 func (h *Host) schedulerRecord() *capabilityRecord {
 	if h == nil {
 		return nil

sdk/cliproxy/auth/conductor.go

@@ -126,6 +126,10 @@ type PluginScheduler interface {
 	PickAuth(context.Context, pluginapi.SchedulerPickRequest) (pluginapi.SchedulerPickResponse, bool, error)
 }
 
+type pluginSchedulerState interface {
+	HasScheduler() bool
+}
+
 // StoppableSelector is an optional interface for selectors that hold resources.
 // Selectors that implement this interface will have Stop called during shutdown.
 type StoppableSelector interface {
@@ -245,9 +249,15 @@ func (m *Manager) hasPluginScheduler() bool {
 		return false
 	}
 	m.mu.RLock()
-	ok := m.pluginScheduler != nil
+	scheduler := m.pluginScheduler
 	m.mu.RUnlock()
-	return ok
+	if scheduler == nil {
+		return false
+	}
+	if state, ok := scheduler.(pluginSchedulerState); ok {
+		return state.HasScheduler()
+	}
+	return true
 }
 
 func isBuiltInSelector(selector Selector) bool {

sdk/cliproxy/auth/scheduler_test.go

@@ -55,6 +55,14 @@ func (s *fakePluginScheduler) PickAuth(ctx context.Context, req pluginapi.Schedu
 	return s.resp, s.handled, s.err
 }
 
+type inactivePluginScheduler struct {
+	fakePluginScheduler
+}
+
+func (s *inactivePluginScheduler) HasScheduler() bool {
+	return false
+}
+
 type trackingSelector struct {
 	calls      int
 	lastAuthID []string
@@ -440,6 +448,38 @@ func TestManagerPluginSchedulerSkippedWhenHomeEnabled(t *testing.T) {
 	}
 }
 
+func TestManagerInactivePluginSchedulerKeepsFastPath(t *testing.T) {
+	manager := NewManager(nil, &RoundRobinSelector{}, nil)
+	manager.executors["gemini"] = schedulerTestExecutor{}
+	if _, errRegister := manager.Register(context.Background(), &Auth{ID: "auth-a", Provider: "gemini"}); errRegister != nil {
+		t.Fatalf("Register(auth-a) error = %v", errRegister)
+	}
+	if _, errRegister := manager.Register(context.Background(), &Auth{ID: "auth-b", Provider: "gemini"}); errRegister != nil {
+		t.Fatalf("Register(auth-b) error = %v", errRegister)
+	}
+
+	scheduler := &inactivePluginScheduler{}
+	manager.SetPluginScheduler(scheduler)
+
+	gotA, _, errPick := manager.pickNext(context.Background(), "gemini", "", cliproxyexecutor.Options{}, nil)
+	if errPick != nil {
+		t.Fatalf("pickNext() first error = %v", errPick)
+	}
+	gotB, _, errPick := manager.pickNext(context.Background(), "gemini", "", cliproxyexecutor.Options{}, nil)
+	if errPick != nil {
+		t.Fatalf("pickNext() second error = %v", errPick)
+	}
+	if gotA == nil || gotB == nil {
+		t.Fatalf("pickNext() auths = %v, %v; want non-nil", gotA, gotB)
+	}
+	if gotA.ID != "auth-a" || gotB.ID != "auth-b" {
+		t.Fatalf("fast path picks = %q, %q; want auth-a, auth-b", gotA.ID, gotB.ID)
+	}
+	if scheduler.calls != 0 {
+		t.Fatalf("scheduler.calls = %d, want %d", scheduler.calls, 0)
+	}
+}
+
 func TestManagerPluginSchedulerCalledOutsideManagerLock(t *testing.T) {
 	manager := NewManager(nil, &RoundRobinSelector{}, nil)
 	manager.executors["gemini"] = schedulerTestExecutor{}
@@ -645,6 +685,38 @@ func TestManagerPluginSchedulerPickNextMixedSelectsProvider(t *testing.T) {
 	}
 }
 
+func TestManagerInactivePluginSchedulerKeepsMixedFastPath(t *testing.T) {
+	manager := NewManager(nil, &RoundRobinSelector{}, nil)
+	manager.executors["gemini"] = schedulerTestExecutor{}
+	manager.executors["claude"] = schedulerTestExecutor{}
+	if _, errRegister := manager.Register(context.Background(), &Auth{ID: "gemini-a", Provider: "gemini"}); errRegister != nil {
+		t.Fatalf("Register(gemini-a) error = %v", errRegister)
+	}
+	if _, errRegister := manager.Register(context.Background(), &Auth{ID: "claude-a", Provider: "claude"}); errRegister != nil {
+		t.Fatalf("Register(claude-a) error = %v", errRegister)
+	}
+
+	scheduler := &inactivePluginScheduler{}
+	manager.SetPluginScheduler(scheduler)
+
+	got, _, provider, errPick := manager.pickNextMixed(context.Background(), []string{"gemini", "claude"}, "", cliproxyexecutor.Options{}, nil)
+	if errPick != nil {
+		t.Fatalf("pickNextMixed() error = %v", errPick)
+	}
+	if got == nil {
+		t.Fatalf("pickNextMixed() auth = nil")
+	}
+	if provider != "gemini" {
+		t.Fatalf("pickNextMixed() provider = %q, want gemini", provider)
+	}
+	if got.ID != "gemini-a" {
+		t.Fatalf("pickNextMixed() auth.ID = %q, want gemini-a", got.ID)
+	}
+	if scheduler.calls != 0 {
+		t.Fatalf("scheduler.calls = %d, want %d", scheduler.calls, 0)
+	}
+}
+
 func TestManagerPluginSchedulerCandidatesAreSafeCopies(t *testing.T) {
 	manager := NewManager(nil, &RoundRobinSelector{}, nil)
 	manager.executors["gemini"] = schedulerTestExecutor{}