Add campaign configuration support

internal/app/campaign_config_path_test.go

@@ -0,0 +1,49 @@
+package app
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestResolveCampaignConfigPathExplicitWins(t *testing.T) {
+	explicit := filepath.Join(t.TempDir(), "custom-campaign.yml")
+	got, err := resolveCampaignConfigPathWithCandidates(explicit, []string{filepath.Join(t.TempDir(), "campaign.yml")})
+	if err != nil {
+		t.Fatalf("resolveCampaignConfigPathWithCandidates() error = %v", err)
+	}
+	if got != explicit {
+		t.Fatalf("path = %q, want explicit path %q", got, explicit)
+	}
+}
+
+func TestResolveCampaignConfigPathUsesFirstExistingDefault(t *testing.T) {
+	dir := t.TempDir()
+	missing := filepath.Join(dir, "missing.yml")
+	found := filepath.Join(dir, "campaign.yml")
+	if err := os.WriteFile(found, []byte("campaign: sample-campaign\n"), 0o644); err != nil {
+		t.Fatalf("write campaign.yml: %v", err)
+	}
+
+	got, err := resolveCampaignConfigPathWithCandidates("", []string{missing, found})
+	if err != nil {
+		t.Fatalf("resolveCampaignConfigPathWithCandidates() error = %v", err)
+	}
+	if got != filepath.Clean(found) {
+		t.Fatalf("path = %q, want %q", got, filepath.Clean(found))
+	}
+}
+
+func TestResolveCampaignConfigPathErrorIncludesSearchedPaths(t *testing.T) {
+	_, err := resolveCampaignConfigPathWithCandidates("", []string{"./campaign.yml", "/usr/local/etc/narratio/campaign.yml", "/etc/narratio/campaign.yml"})
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+	if !strings.Contains(err.Error(), "searched") {
+		t.Fatalf("error = %q, want searched paths", err.Error())
+	}
+	if !strings.Contains(err.Error(), "pass --campaign") {
+		t.Fatalf("error = %q, want explicit-campaign guidance", err.Error())
+	}
+}