Skip area version-only extract churn (#28)

## Summary
- skip overwriting existing `.are.json` files when only the root GFF `Version` differs
- keep real extraction changes writing normally
- add regression coverage for version-only area extraction

## Test Plan
- `nix develop --command make check`
- sample extraction in a clean temp `sow-module` clone using the patched `crucible` binary

Reviewed-on: #28
Reviewed-by: xtul <mpiasecki720@protonmail.com>
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

internal/pipeline/extract.go

@@ -501,6 +501,9 @@ func writeManagedFile(path string, data []byte) (writeState, error) {
 		if bytes.Equal(existing, data) {
 			return writeSkipped, nil
 		}
+		if areaGFFJSONEqualIgnoringRootVersion(path, existing, data) {
+			return writeSkipped, nil
+		}
 		if err := os.WriteFile(path, data, 0o644); err != nil {
 			return writeSkipped, fmt.Errorf("overwrite %s: %w", path, err)
 		}
@@ -516,6 +519,38 @@ func writeManagedFile(path string, data []byte) (writeState, error) {
 	return writeNew, nil
 }
 
+func areaGFFJSONEqualIgnoringRootVersion(path string, existing, extracted []byte) bool {
+	if !strings.HasSuffix(strings.ToLower(filepath.Base(path)), ".are.json") {
+		return false
+	}
+
+	var left, right gff.Document
+	if err := json.Unmarshal(existing, &left); err != nil {
+		return false
+	}
+	if err := json.Unmarshal(extracted, &right); err != nil {
+		return false
+	}
+	removeRootField(&left.Root, "Version")
+	removeRootField(&right.Root, "Version")
+
+	leftRaw, err := json.Marshal(left)
+	if err != nil {
+		return false
+	}
+	rightRaw, err := json.Marshal(right)
+	if err != nil {
+		return false
+	}
+	return bytes.Equal(leftRaw, rightRaw)
+}
+
+func removeRootField(s *gff.Struct, label string) {
+	s.Fields = slices.DeleteFunc(s.Fields, func(field gff.Field) bool {
+		return field.Label == label
+	})
+}
+
 func cleanupStaleFiles(p *project.Project, desired map[string]struct{}, scope extractionScope) (int, []error) {
 	candidates := make([]string, 0, len(p.Inventory.SourceFiles)+len(p.Inventory.ScriptFiles)+len(p.Inventory.AssetFiles))
 	if scope.Source && safeCleanupRoot(p.SourceDir(), p.Root) {

internal/pipeline/pipeline_test.go

@@ -134,6 +134,113 @@ func TestBuildThenExtract(t *testing.T) {
 	}
 }
 
+func TestExtractSkipsAreaWhenOnlyRootVersionChanges(t *testing.T) {
+	root := t.TempDir()
+	mustMkdir(t, filepath.Join(root, "src", "module"))
+	mustMkdir(t, filepath.Join(root, "src", "areas"))
+	mustMkdir(t, filepath.Join(root, "assets"))
+	mustMkdir(t, filepath.Join(root, "build"))
+
+	mustWriteFile(t, filepath.Join(root, "nwn-tool.json"), `{
+  "module": {
+    "name": "Test Module",
+    "resref": "testmod"
+  },
+  "paths": {
+    "source": "src",
+    "assets": "assets",
+    "build": "build"
+  }
+}
+`)
+	mustWriteFile(t, filepath.Join(root, "src", "module", "module.ifo.json"), `{
+  "file_type": "IFO ",
+  "file_version": "V3.2",
+  "root": {
+    "struct_type": 0,
+    "fields": [
+      {
+        "label": "Mod_Name",
+        "type": "CExoString",
+        "value": "Test Module"
+      }
+    ]
+  }
+}
+`)
+	mustWriteFile(t, filepath.Join(root, "src", "areas", "area001.are.json"), `{
+  "file_type": "ARE ",
+  "file_version": "V3.2",
+  "root": {
+    "struct_type": 0,
+    "fields": [
+      {
+        "label": "Version",
+        "type": "DWord",
+        "value": 2
+      },
+      {
+        "label": "Tag",
+        "type": "CExoString",
+        "value": "area001"
+      }
+    ]
+  }
+}
+`)
+
+	p, err := project.Load(root)
+	if err != nil {
+		t.Fatalf("load project: %v", err)
+	}
+	if err := p.ValidateLayout(); err != nil {
+		t.Fatalf("validate layout: %v", err)
+	}
+	if err := p.Scan(); err != nil {
+		t.Fatalf("scan: %v", err)
+	}
+	if _, err := BuildModule(p); err != nil {
+		t.Fatalf("build module: %v", err)
+	}
+
+	mustWriteFile(t, filepath.Join(root, "src", "areas", "area001.are.json"), `{
+  "file_type": "ARE ",
+  "file_version": "V3.2",
+  "root": {
+    "struct_type": 0,
+    "fields": [
+      {
+        "label": "Version",
+        "type": "DWord",
+        "value": 1
+      },
+      {
+        "label": "Tag",
+        "type": "CExoString",
+        "value": "area001"
+      }
+    ]
+  }
+}
+`)
+	if err := p.Scan(); err != nil {
+		t.Fatalf("rescan: %v", err)
+	}
+
+	result, err := Extract(p)
+	if err != nil {
+		t.Fatalf("extract: %v", err)
+	}
+	if result.Overwritten != 0 {
+		t.Fatalf("Version-only area extraction must not overwrite, got %d overwritten", result.Overwritten)
+	}
+
+	document := readGFFJSON(t, filepath.Join(root, "src", "areas", "area001.are.json"))
+	if got, want := fieldValue(t, document.Root, "Version"), gff.DWordValue(1); got != want {
+		t.Fatalf("expected existing Version %#v to remain, got %#v", want, got)
+	}
+}
+
 func TestExtractReadsHAKAssets(t *testing.T) {
 	root := t.TempDir()
 	mustMkdir(t, filepath.Join(root, "src"))