fix(project): a module resref names a file, not a resource

module.resref is the name of the built .mod on disk, so the 16-byte resref
limit never applied to it — NWN:EE module file names are routinely longer.
The blanket check rejected ShadowsOverWestgate (19 characters) and blocked
sow-module#60.

It is now validated as a file name instead, which still rejects a resref
that is a path or an empty string.

The limit is kept where the value really does become a resref: a project
with paths.assets and no haks[] names its single generated HAK after the
module resref, and a HAK name is a resref the engine loads. That case now
says what to do about it rather than refusing every long module name.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/project/project_test.go

@@ -1093,6 +1093,78 @@ func TestValidateLayoutAllowsMissingAssetsDir(t *testing.T) {
 	}
 }
 
+// module.resref names the built .mod FILE, not a resource inside an archive, so the
+// 16-byte resref limit does not apply to it. NWN:EE module file names are commonly
+// longer (ShadowsOverWestgate.mod is 19). The limit still binds everywhere a resref
+// really is a resref — see TestValidateLayoutRejectsLongResRefWhenItNamesAHAK.
+func TestValidateLayoutAllowsLongModuleResRef(t *testing.T) {
+	root := t.TempDir()
+	mkdirAll(t, filepath.Join(root, "src"))
+	mkdirAll(t, filepath.Join(root, "build"))
+
+	proj := &Project{
+		Root: root,
+		Config: Config{
+			Module: ModuleConfig{Name: "Shadows Over Westgate", ResRef: "ShadowsOverWestgate"},
+			Paths:  PathConfig{Source: "src", Build: "build"},
+		},
+	}
+
+	if err := proj.ValidateLayout(); err != nil {
+		t.Fatalf("ValidateLayout rejected a 19-character module file name: %v", err)
+	}
+	if got, want := filepath.Base(proj.ModuleArchivePath()), "ShadowsOverWestgate.mod"; got != want {
+		t.Fatalf("ModuleArchivePath() = %q, want %q", got, want)
+	}
+}
+
+// A module.resref that is not a usable file name is still rejected.
+func TestValidateLayoutRejectsModuleResRefThatIsAPath(t *testing.T) {
+	root := t.TempDir()
+	mkdirAll(t, filepath.Join(root, "src"))
+
+	proj := &Project{
+		Root: root,
+		Config: Config{
+			Module: ModuleConfig{Name: "Test", ResRef: "../escape/mod"},
+			Paths:  PathConfig{Source: "src", Build: "build"},
+		},
+	}
+
+	err := proj.ValidateLayout()
+	if err == nil {
+		t.Fatal("ValidateLayout accepted a module.resref containing a path")
+	}
+	if !strings.Contains(err.Error(), "module.resref") {
+		t.Fatalf("error does not name the offending field: %v", err)
+	}
+}
+
+// When a project declares no haks, the module resref becomes the name of the single
+// generated HAK — and a HAK name IS a resref the engine loads. The limit applies
+// there, so a long name is only allowed for projects that build no HAKs.
+func TestValidateLayoutRejectsLongResRefWhenItNamesAHAK(t *testing.T) {
+	root := t.TempDir()
+	mkdirAll(t, filepath.Join(root, "src"))
+	mkdirAll(t, filepath.Join(root, "assets"))
+
+	proj := &Project{
+		Root: root,
+		Config: Config{
+			Module: ModuleConfig{Name: "Shadows Over Westgate", ResRef: "ShadowsOverWestgate"},
+			Paths:  PathConfig{Source: "src", Assets: "assets", Build: "build"},
+		},
+	}
+
+	err := proj.ValidateLayout()
+	if err == nil {
+		t.Fatal("ValidateLayout accepted a 19-character name for a generated HAK")
+	}
+	if !strings.Contains(err.Error(), "16") {
+		t.Fatalf("error does not explain the resref limit: %v", err)
+	}
+}
+
 // paths.build is an OUTPUT dir the builder creates (MkdirAll) before writing, so
 // a bare clone with no build dir yet must still validate/build with no pre-step
 // (R2/parity). Only a build path that exists but is not a directory is an error.