config: Default() returns error

Default() now returns (*Config, error) so callers can detect TOML parse
failures rather than silently falling back to zero values.

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

2 files changed, 35 insertions, 3 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index da7f264..12adf68 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -1,6 +1,8 @@
 package config
 
 import (
+	"errors"
+	"fmt"
 	"os"
 	"path/filepath"
 )
@@ -16,8 +18,14 @@ type Config struct {
 	WebhookURL       string `toml:"webhook_url"`
 }
 
-func Default() *Config {
-	home, _ := os.UserHomeDir()
+func Default() (*Config, error) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return nil, fmt.Errorf("cannot determine home directory: %w", err)
+	}
+	if home == "" {
+		return nil, errors.New("cannot determine home directory: HOME is empty")
+	}
 	dataDir := filepath.Join(home, ".claudomator")
 	return &Config{
 		DataDir:          dataDir,
@@ -27,7 +35,7 @@ func Default() *Config {
 		MaxConcurrent:    3,
 		DefaultTimeout:   "15m",
 		ServerAddr:       ":8484",
-	}
+	}, nil
 }
 
 // EnsureDirs creates the data directory structure.
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
new file mode 100644
index 0000000..766b856
--- /dev/null
+++ b/internal/config/config_test.go
@@ -0,0 +1,24 @@
+package config
+
+import (
+	"testing"
+)
+
+func TestDefault_EmptyHome_ReturnsError(t *testing.T) {
+	t.Setenv("HOME", "")
+	_, err := Default()
+	if err == nil {
+		t.Fatal("expected error when HOME is empty, got nil")
+	}
+}
+
+func TestDefault_ValidHome_ReturnsConfig(t *testing.T) {
+	t.Setenv("HOME", "/tmp/testhome")
+	cfg, err := Default()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if cfg.DataDir != "/tmp/testhome/.claudomator" {
+		t.Errorf("DataDir = %q, want /tmp/testhome/.claudomator", cfg.DataDir)
+	}
+}