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>

1 files changed, 24 insertions, 0 deletions

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)
+	}
+}