fix: allow skill_manage companion files

Squash merge PR #104 after validation.

internal/http/skills_versions_test.go

@@ -3,6 +3,7 @@ package http
 import (
 	"os"
 	"path/filepath"
+	"slices"
 	"testing"
 )
 
@@ -32,3 +33,37 @@ func TestReadableSkillRootsDoesNotFallbackForCustomSkill(t *testing.T) {
 		t.Fatalf("roots = %#v, want no custom fallback", roots)
 	}
 }
+
+func TestSkillVersionReadbackListsAndReadsCompanionReferenceFiles(t *testing.T) {
+	t.Parallel()
+	tmp := t.TempDir()
+	versionDir := filepath.Join(tmp, "managed", "demo", "2")
+	referencePath := filepath.Join(versionDir, "references", "ship-workflow.md")
+	if err := os.MkdirAll(filepath.Dir(referencePath), 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(versionDir, "SKILL.md"), []byte("---\nname: Demo\n---\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(referencePath, []byte("# Ship\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	files := walkSkillFiles(versionDir)
+	if !slices.ContainsFunc(files, func(entry fileEntry) bool {
+		return entry.Path == filepath.Join("references", "ship-workflow.md") && !entry.IsDir && entry.Size == int64(len("# Ship\n"))
+	}) {
+		t.Fatalf("files = %#v, want references/ship-workflow.md", files)
+	}
+
+	data, info, err := readSkillFile(referencePath)
+	if err != nil {
+		t.Fatalf("readSkillFile: %v", err)
+	}
+	if string(data) != "# Ship\n" {
+		t.Fatalf("content = %q", data)
+	}
+	if info.Size() != int64(len("# Ship\n")) {
+		t.Fatalf("size = %d", info.Size())
+	}
+}