fix(project): a module resref names a file, not a resource (#93)

`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:

```
crucible module build
  module.resref "ShadowsOverWestgate" exceeds 16 characters
```

## What changed

`internal/project/project.go` — `module.resref` is validated as a **file name** now, which still rejects a resref that is a path or empty.

The 16-character 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 (`build.go:1144`), and a HAK name is a resref the engine loads. That case now says what to do about it instead of refusing every long module name.

## Verified

- 3 new tests in `internal/project`: a long module name validates and produces `ShadowsOverWestgate.mod`; a resref containing a path is rejected; a long resref that would name a generated HAK is still rejected.
- `make check` green.
- `crucible module build` in sow-module writes `module/ShadowsOverWestgate.mod` (70 resources).
- `crucible topdata validate` in sow-topdata still passes — its assets live under `topdata.assets`, not `paths.assets`, so the HAK guard does not bite.

Merge this **first**: sow-module's rename PR cannot go green in CI until this lands and its `flake.lock` is bumped.

Refs ShadowsOverWestgate/sow-module#60

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #93

Co-authored-by: vickydotbat <vickydotbat@tutamail.com>

internal/project/project.go

@@ -560,8 +560,18 @@ func (p *Project) ValidateLayout() error {
 	if strings.TrimSpace(p.Config.Module.ResRef) == "" {
 		failures = append(failures, errors.New("module.resref is required"))
 	}
-	if len(p.Config.Module.ResRef) > 16 {
-		failures = append(failures, fmt.Errorf("module.resref %q exceeds 16 characters", p.Config.Module.ResRef))
+	// module.resref names the built .mod FILE, so the 16-byte resref limit does not
+	// apply to it — NWN:EE module file names are routinely longer. It is validated as
+	// a file name instead. The limit still binds when the same value has to be a real
+	// resref: with no haks configured, an asset project names its single generated HAK
+	// after it, and a HAK name is a resref the engine loads.
+	if err := validateOutputFileName("module.resref", p.Config.Module.ResRef+".mod", ".mod"); err != nil {
+		failures = append(failures, err)
+	}
+	if len(p.Config.Module.ResRef) > 16 && strings.TrimSpace(p.Config.Paths.Assets) != "" && len(p.Config.HAKs) == 0 {
+		failures = append(failures, fmt.Errorf(
+			"module.resref %q exceeds 16 characters and would name this project's generated HAK; configure haks[] with a shorter name",
+			p.Config.Module.ResRef))
 	}
 	if strings.TrimSpace(p.Config.Paths.Source) == "" && strings.TrimSpace(p.Config.Paths.Assets) == "" && !p.HasTopData() {
 		failures = append(failures, errors.New("at least one of paths.source, paths.assets, or topdata.source is required"))

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.