fix: resolve correct provider for plan_model with different provider prefix

When plan_model uses a different provider than the main model (e.g.,
plan_model="openai/gpt-5.2" with main provider=minimax), the single-
candidate code path was sending the raw model string to the wrong
provider. Now uses resolveProvider() to create the correct provider
instance and pass the stripped model name.

Also adds "openai" to normalizeModel's prefix list as a defensive
measure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/agent/loop.go

@@ -1668,6 +1668,11 @@ func (al *AgentLoop) runLLMIteration(
 				}
 				return fbResult.Response, nil
 			}
+			if len(candidates) > 0 {
+				c := candidates[0]
+				p := al.resolveProvider(c.Provider, c.Model, agent.Provider)
+				return doCall(ctx, p, c.Model)
+			}
 			return doCall(ctx, agent.Provider, primaryModel)
 		}
 

pkg/agent/loop_test.go

@@ -2505,6 +2505,75 @@ func TestAgentLoop_PlanModel_NotUsedDuringExecuting(t *testing.T) {
 	}
 }
 
+func TestAgentLoop_PlanModel_ResolvesProviderForSingleCandidate(t *testing.T) {
+	tmpDir, err := os.MkdirTemp("", "agent-test-planmodel-resolve-*")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	cfg := &config.Config{
+		Agents: config.AgentsConfig{
+			Defaults: config.AgentDefaults{
+				Workspace:         tmpDir,
+				Model:             "MiniMax-M2.5",
+				PlanModel:         "openai/gpt-5.2",
+				MaxTokens:         4096,
+				MaxToolIterations: 2,
+			},
+		},
+	}
+
+	msgBus := bus.NewMessageBus()
+	// The main provider simulates the wrong provider (e.g. MiniMax).
+	mainProvider := &modelCapturingMockProvider{response: "wrong provider response"}
+	al := NewAgentLoop(cfg, msgBus, mainProvider)
+
+	// Inject a mock provider into the cache so resolveProvider returns it
+	// for the "openai/gpt-5.2" candidate (provider="openai", model="gpt-5.2").
+	resolvedProvider := &modelCapturingMockProvider{response: "correct provider response"}
+	al.providerCache["openai/gpt-5.2"] = resolvedProvider
+
+	// Write MEMORY.md with interviewing status to activate plan model
+	memoryDir := filepath.Join(tmpDir, "memory")
+	os.MkdirAll(memoryDir, 0o755)
+	memoryPath := filepath.Join(memoryDir, "MEMORY.md")
+	memoryContent := "# Active Plan\n\n> Task: Test provider resolution\n> Status: interviewing\n> Phase: 1\n"
+	if err := os.WriteFile(memoryPath, []byte(memoryContent), 0o644); err != nil {
+		t.Fatalf("Failed to write MEMORY.md: %v", err)
+	}
+
+	_, err = al.ProcessDirectWithChannel(
+		context.Background(),
+		"Hello, resolve provider test",
+		"test-resolve-session",
+		"test",
+		"test-chat",
+	)
+	if err != nil {
+		t.Fatalf("ProcessDirectWithChannel failed: %v", err)
+	}
+
+	resolvedProvider.mu.Lock()
+	defer resolvedProvider.mu.Unlock()
+	mainProvider.mu.Lock()
+	defer mainProvider.mu.Unlock()
+
+	// The resolved provider should have been called with the stripped model name
+	if len(resolvedProvider.models) == 0 {
+		t.Fatal("Expected resolved provider to receive Chat call, but it got none")
+	}
+	if resolvedProvider.models[0] != "gpt-5.2" {
+		t.Errorf("Expected resolved provider to receive model 'gpt-5.2', got %q", resolvedProvider.models[0])
+	}
+
+	// The main provider should NOT have been called for the LLM request
+	if len(mainProvider.models) > 0 {
+		t.Errorf("Expected main provider to receive no Chat calls during plan model phase, got %d calls with models %v",
+			len(mainProvider.models), mainProvider.models)
+	}
+}
+
 func TestPlanCommand_StartClear(t *testing.T) {
 	al, cleanup := newTestAgentLoop(t)
 	defer cleanup()

pkg/providers/openai_compat/provider.go

@@ -470,7 +470,7 @@ func normalizeModel(model, apiBase string) string {
 
 	prefix := strings.ToLower(model[:idx])
 	switch prefix {
-	case "moonshot", "nvidia", "groq", "ollama", "deepseek", "google", "openrouter", "zhipu", "minimax", "mistral":
+	case "openai", "moonshot", "nvidia", "groq", "ollama", "deepseek", "google", "openrouter", "zhipu", "minimax", "mistral":
 		return model[idx+1:]
 	default:
 		return model

pkg/providers/openai_compat/provider_test.go

@@ -287,6 +287,12 @@ func TestNormalizeModel_UsesAPIBase(t *testing.T) {
 	}
 }
 
+func TestNormalizeModel_OpenAIPrefix(t *testing.T) {
+	if got := normalizeModel("openai/gpt-5.2", "https://api.openai.com/v1"); got != "gpt-5.2" {
+		t.Fatalf("normalizeModel(openai/gpt-5.2) = %q, want %q", got, "gpt-5.2")
+	}
+}
+
 func TestProviderChat_StreamingTextResponse(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != "/text/chatcompletion_v2" {