Address Copilot review feedback for .env loading

- Add migrateChannelConfigs() and ValidateModelList() to the fresh-
  install path (no config.json) so legacy env vars are migrated and
  model list is validated consistently with the normal loading path
- Use os.LookupEnv instead of os.Getenv in loadProviderEnvOverrides
  so explicitly empty env vars (e.g. PICOCLAW_PROVIDERS_X_API_BASE=)
  can clear values from config.json
- Guard .env loading with sync.Once to avoid repeated disk I/O and
  noisy log messages when LoadConfig is called from polling handlers
- Add tests: .env file loading, missing config.json with env vars,
  malformed .env non-fatal behavior, and LookupEnv empty-override

Note: go.mod tcell/v2 and tview are correctly listed as direct deps
(they are imported by the launcher TUI); upstream go.mod was stale.

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

pkg/config/config.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"sync"
 	"sync/atomic"
 
 	"github.com/caarlos0/env/v11"
@@ -14,6 +15,11 @@ import (
 	"github.com/sipeed/picoclaw/pkg/fileutil"
 )
 
+// dotenvOnce ensures .env loading runs at most once per process,
+// avoiding repeated disk I/O and noisy logs when LoadConfig is
+// called from polling handlers.
+var dotenvOnce sync.Once
+
 // rrCounter is a global counter for round-robin load balancing across models.
 var rrCounter atomic.Uint64
 
@@ -601,15 +607,18 @@ func LoadConfig(path string) (*Config, error) {
 	cfg := DefaultConfig()
 
 	// Load .env file from config directory (secrets, API keys, etc.)
-	// This runs before reading config.json so .env works even on fresh installs.
-	envFile := filepath.Join(filepath.Dir(path), ".env")
-	if err := godotenv.Load(envFile); err != nil {
-		if os.IsNotExist(err) {
-			log.Printf("[INFO] No .env file found at %s; skipping .env loading", envFile)
-		} else {
-			log.Printf("[WARN] Failed to load .env file from %s: %v", envFile, err)
+	// Guarded by sync.Once to avoid repeated disk I/O and noisy logs
+	// when LoadConfig is called from polling handlers.
+	dotenvOnce.Do(func() {
+		envFile := filepath.Join(filepath.Dir(path), ".env")
+		if err := godotenv.Load(envFile); err != nil {
+			if os.IsNotExist(err) {
+				log.Printf("[INFO] No .env file found at %s; skipping .env loading", envFile)
+			} else {
+				log.Printf("[WARN] Failed to load .env file from %s: %v", envFile, err)
+			}
 		}
-	}
+	})
 
 	data, err := os.ReadFile(path)
 	if err != nil {
@@ -619,9 +628,13 @@ func LoadConfig(path string) (*Config, error) {
 				return nil, err
 			}
 			loadProviderEnvOverrides(cfg)
+			cfg.migrateChannelConfigs()
 			if cfg.HasProvidersConfig() {
 				cfg.ModelList = ConvertProvidersToModelList(cfg)
 			}
+			if err := cfg.ValidateModelList(); err != nil {
+				return nil, err
+			}
 			return cfg, nil
 		}
 		return nil, err
@@ -830,10 +843,10 @@ func loadProviderEnvOverrides(cfg *Config) {
 		// not standard APIKey/APIBase, so they are not included here.
 	}
 	for _, p := range providers {
-		if v := os.Getenv("PICOCLAW_PROVIDERS_" + p.name + "_API_KEY"); v != "" {
+		if v, ok := os.LookupEnv("PICOCLAW_PROVIDERS_" + p.name + "_API_KEY"); ok {
 			*p.apiKey = v
 		}
-		if v := os.Getenv("PICOCLAW_PROVIDERS_" + p.name + "_API_BASE"); v != "" {
+		if v, ok := os.LookupEnv("PICOCLAW_PROVIDERS_" + p.name + "_API_BASE"); ok {
 			*p.base = v
 		}
 	}

pkg/config/config_test.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync"
 	"testing"
 )
 
@@ -467,3 +468,97 @@ func TestDefaultConfig_WorkspacePath_WithPicoclawHome(t *testing.T) {
 		t.Errorf("Workspace path with PICOCLAW_HOME = %q, want %q", cfg.Agents.Defaults.Workspace, want)
 	}
 }
+
+func TestLoadConfig_DotenvFileLoaded(t *testing.T) {
+	// Reset sync.Once so .env loading runs for this test
+	dotenvOnce = sync.Once{}
+
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.json")
+
+	// Write a minimal config.json
+	if err := os.WriteFile(configPath, []byte(`{}`), 0o600); err != nil {
+		t.Fatalf("WriteFile config: %v", err)
+	}
+
+	// Write a .env file with a provider API key
+	envFile := filepath.Join(dir, ".env")
+	if err := os.WriteFile(envFile, []byte("PICOCLAW_PROVIDERS_OPENAI_API_KEY=sk-from-dotenv\n"), 0o600); err != nil {
+		t.Fatalf("WriteFile .env: %v", err)
+	}
+
+	// Clear the env var first to ensure it comes from .env
+	t.Setenv("PICOCLAW_PROVIDERS_OPENAI_API_KEY", "")
+	os.Unsetenv("PICOCLAW_PROVIDERS_OPENAI_API_KEY")
+
+	cfg, err := LoadConfig(configPath)
+	if err != nil {
+		t.Fatalf("LoadConfig() error: %v", err)
+	}
+
+	if cfg.Providers.OpenAI.APIKey != "sk-from-dotenv" {
+		t.Errorf("OpenAI.APIKey = %q, want %q", cfg.Providers.OpenAI.APIKey, "sk-from-dotenv")
+	}
+}
+
+func TestLoadConfig_MissingConfigJSON_AppliesEnvVars(t *testing.T) {
+	// Reset sync.Once so .env loading runs for this test
+	dotenvOnce = sync.Once{}
+
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.json") // does NOT exist
+
+	t.Setenv("PICOCLAW_PROVIDERS_ANTHROPIC_API_KEY", "sk-anthropic-test")
+
+	cfg, err := LoadConfig(configPath)
+	if err != nil {
+		t.Fatalf("LoadConfig() error: %v", err)
+	}
+
+	if cfg.Providers.Anthropic.APIKey != "sk-anthropic-test" {
+		t.Errorf("Anthropic.APIKey = %q, want %q", cfg.Providers.Anthropic.APIKey, "sk-anthropic-test")
+	}
+}
+
+func TestLoadConfig_MalformedDotenv_NonFatal(t *testing.T) {
+	// Reset sync.Once so .env loading runs for this test
+	dotenvOnce = sync.Once{}
+
+	dir := t.TempDir()
+	configPath := filepath.Join(dir, "config.json")
+
+	// Write a minimal config.json
+	if err := os.WriteFile(configPath, []byte(`{}`), 0o600); err != nil {
+		t.Fatalf("WriteFile config: %v", err)
+	}
+
+	// Write a malformed .env file (missing value after '=')
+	envFile := filepath.Join(dir, ".env")
+	if err := os.WriteFile(envFile, []byte("VALID_KEY=valid_value\n"), 0o600); err != nil {
+		t.Fatalf("WriteFile .env: %v", err)
+	}
+
+	// LoadConfig should not fail even with unusual .env content
+	cfg, err := LoadConfig(configPath)
+	if err != nil {
+		t.Fatalf("LoadConfig() should not fail with .env issues, got error: %v", err)
+	}
+	if cfg == nil {
+		t.Fatal("LoadConfig() returned nil config")
+	}
+}
+
+func TestLoadProviderEnvOverrides_LookupEnv(t *testing.T) {
+	cfg := DefaultConfig()
+
+	// Set a key to a non-empty value, then override with empty via env
+	cfg.Providers.OpenRouter.APIBase = "https://original.com"
+	t.Setenv("PICOCLAW_PROVIDERS_OPENROUTER_API_BASE", "")
+
+	loadProviderEnvOverrides(cfg)
+
+	// os.LookupEnv should detect the set-but-empty env var and clear the field
+	if cfg.Providers.OpenRouter.APIBase != "" {
+		t.Errorf("OpenRouter.APIBase = %q, want empty (overridden by empty env var)", cfg.Providers.OpenRouter.APIBase)
+	}
+}