fix: phase 8 refactoring

REFACTOR_DUPLICATION.md

@@ -262,7 +262,7 @@ Move color contrast logic into a shared renderer utility.
 2. Phase 2 (finish TagEngine workflow dedup)
 3. Phase 3 (finish PostMedia single/batch dedup)
 4. ~~Phase 7 (WxrParser repeated parse blocks)~~ ✅ Completed
-5. Phase 8 (MetaEngine ↔ TagEngine overlap)
+5. ~~Phase 8 (MetaEngine ↔ TagEngine overlap)~~ ✅ Completed
 6. Phase 9 (renderer tag event subscription helper)
 7. Phase 10 (local UI repeated blocks in component files)
 
@@ -307,6 +307,8 @@ Extract shared `parsePubDate` and/or shared item base builder helper to avoid dr
 
 ## Phase 8 — Merge Shared Taxonomy/Metadata Logic (MetaEngine + TagEngine)
 
+Status: ✅ Completed
+
 ### Problem
 A medium-sized duplicate block appears across `MetaEngine` and `TagEngine` for taxonomy/tag-style handling.
 
@@ -323,6 +325,10 @@ Extract a shared helper module or internal utility used by both engines.
 - Equivalent behavior in both engines.
 - Single implementation for overlapping logic.
 
+### Progress Check
+- Completed: extracted shared taxonomy normalization/collection helper and adopted it in both engines.
+- Completed: added cross-engine normalization tests (including empty/whitespace filtering parity).
+
 ### Coverage & Test Quality (fresh run: `npm run test:coverage`)
 - `src/main/engine/MetaEngine.ts`: 95.03% statements, 96.55% functions, 77.59% branches.
 - `src/main/engine/TagEngine.ts`: 95.98% statements, 98.00% functions, 77.89% branches.

src/main/engine/MetaEngine.ts

@@ -5,6 +5,11 @@ import { app } from 'electron';
 import { eq } from 'drizzle-orm';
 import { getDatabase } from '../database';
 import { posts, projects } from '../database/schema';
+import {
+  normalizeTaxonomyTerm,
+  normalizeNonEmptyTaxonomyTerm,
+  collectNormalizedTermsFromJsonValues,
+} from './taxonomyUtils';
 
 /**
  * Project metadata stored in meta/project.json
@@ -144,7 +149,7 @@ export class MetaEngine extends EventEmitter {
    * Note: Tag persistence is handled by TagEngine.
    */
   async addTag(tag: string): Promise<void> {
-    const normalizedTag = tag.trim().toLowerCase();
+    const normalizedTag = normalizeTaxonomyTerm(tag);
     if (normalizedTag && !this.tags.has(normalizedTag)) {
       this.tags.add(normalizedTag);
       this.emit('tagsChanged', await this.getTags());
@@ -156,7 +161,7 @@ export class MetaEngine extends EventEmitter {
    * Note: Tag persistence is handled by TagEngine.
    */
   async removeTag(tag: string): Promise<void> {
-    const normalizedTag = tag.trim().toLowerCase();
+    const normalizedTag = normalizeTaxonomyTerm(tag);
     if (this.tags.delete(normalizedTag)) {
       this.emit('tagsChanged', await this.getTags());
     }
@@ -166,7 +171,7 @@ export class MetaEngine extends EventEmitter {
    * Add a new category to the available categories list.
    */
   async addCategory(category: string): Promise<void> {
-    const normalizedCategory = category.trim().toLowerCase();
+    const normalizedCategory = normalizeTaxonomyTerm(category);
     if (normalizedCategory && !this.categories.has(normalizedCategory)) {
       this.categories.add(normalizedCategory);
       this.emit('categoriesChanged', await this.getCategories());
@@ -178,7 +183,7 @@ export class MetaEngine extends EventEmitter {
    * Remove a category from the available categories list.
    */
   async removeCategory(category: string): Promise<void> {
-    const normalizedCategory = category.trim().toLowerCase();
+    const normalizedCategory = normalizeTaxonomyTerm(category);
     if (this.categories.delete(normalizedCategory)) {
       this.emit('categoriesChanged', await this.getCategories());
       await this.saveCategories();
@@ -244,7 +249,10 @@ export class MetaEngine extends EventEmitter {
       const parsed = JSON.parse(content) as string[];
       this.categories.clear();
       for (const cat of parsed) {
-        this.categories.add(cat.trim().toLowerCase());
+        const normalizedCategory = normalizeNonEmptyTaxonomyTerm(cat);
+        if (normalizedCategory) {
+          this.categories.add(normalizedCategory);
+        }
       }
     } catch (error) {
       if ((error as NodeJS.ErrnoException).code !== 'ENOENT') {
@@ -266,21 +274,7 @@ export class MetaEngine extends EventEmitter {
       .where(eq(posts.projectId, this.currentProjectId))
       .all();
 
-    const allTags = new Set<string>();
-    for (const row of dbPosts) {
-      if (row.tags) {
-        try {
-          const parsed: string[] = JSON.parse(row.tags);
-          for (const tag of parsed) {
-            allTags.add(tag.trim().toLowerCase());
-          }
-        } catch {
-          // Invalid JSON, skip
-        }
-      }
-    }
-
-    return Array.from(allTags).sort();
+    return collectNormalizedTermsFromJsonValues(dbPosts.map((row) => row.tags));
   }
 
   /**
@@ -294,21 +288,7 @@ export class MetaEngine extends EventEmitter {
       .where(eq(posts.projectId, this.currentProjectId))
       .all();
 
-    const allCategories = new Set<string>();
-    for (const row of dbPosts) {
-      if (row.categories) {
-        try {
-          const parsed: string[] = JSON.parse(row.categories);
-          for (const cat of parsed) {
-            allCategories.add(cat.trim().toLowerCase());
-          }
-        } catch {
-          // Invalid JSON, skip
-        }
-      }
-    }
-
-    return Array.from(allCategories).sort();
+    return collectNormalizedTermsFromJsonValues(dbPosts.map((row) => row.categories));
   }
 
   /**

src/main/engine/TagEngine.ts

@@ -8,6 +8,7 @@ import { getDatabase } from '../database';
 import { tags, posts } from '../database/schema';
 import { taskManager } from './TaskManager';
 import { getPostEngine } from './PostEngine';
+import { normalizeTaxonomyTerm, normalizeNonEmptyTaxonomyTerm } from './taxonomyUtils';
 
 /**
  * Tag data stored in the database
@@ -325,7 +326,7 @@ export class TagEngine extends EventEmitter {
   async createTag(input: CreateTagInput): Promise<TagData> {
     const db = this.getDb();
 
-    const name = input.name.trim().toLowerCase();
+    const name = normalizeTaxonomyTerm(input.name);
     if (!name) {
       throw new Error('Tag name is required');
     }
@@ -574,7 +575,7 @@ export class TagEngine extends EventEmitter {
   async renameTag(id: string, newName: string): Promise<RenameTagResult> {
     const db = this.getDb();
 
-    newName = newName.trim().toLowerCase();
+    newName = normalizeTaxonomyTerm(newName);
     if (!newName) {
       throw new Error('New name is required');
     }
@@ -678,7 +679,7 @@ export class TagEngine extends EventEmitter {
    */
   async getTagByName(name: string): Promise<TagData | null> {
     const db = this.getDb();
-    const normalizedName = name.trim().toLowerCase();
+    const normalizedName = normalizeTaxonomyTerm(name);
 
     const rows = await db
       .select()
@@ -763,8 +764,9 @@ export class TagEngine extends EventEmitter {
     for (const row of postRows) {
       const postTags: string[] = JSON.parse(row.tags || '[]');
       for (const tag of postTags) {
-        if (tag.trim()) {
-          discoveredTags.add(tag.trim().toLowerCase());
+        const normalizedTag = normalizeNonEmptyTaxonomyTerm(tag);
+        if (normalizedTag) {
+          discoveredTags.add(normalizedTag);
         }
       }
     }
@@ -861,7 +863,7 @@ export class TagEngine extends EventEmitter {
 
       for (const tag of rawTags) {
         // Support both portable format { name, color? } and legacy format with id
-        const name = (tag.name || '').trim().toLowerCase();
+        const name = normalizeTaxonomyTerm(tag.name || '');
         if (!name) continue;
 
         const color = tag.color || null;

src/main/engine/taxonomyUtils.ts

@@ -0,0 +1,42 @@
+export function normalizeTaxonomyTerm(term: string): string {
+  return term.trim().toLowerCase();
+}
+
+export function normalizeNonEmptyTaxonomyTerm(term: string): string | null {
+  const normalized = normalizeTaxonomyTerm(term);
+  return normalized ? normalized : null;
+}
+
+export function collectNormalizedTermsFromJsonValues(
+  values: Array<string | null | undefined>
+): string[] {
+  const terms = new Set<string>();
+
+  for (const value of values) {
+    if (!value) {
+      continue;
+    }
+
+    try {
+      const parsed = JSON.parse(value) as unknown;
+      if (!Array.isArray(parsed)) {
+        continue;
+      }
+
+      for (const entry of parsed) {
+        if (typeof entry !== 'string') {
+          continue;
+        }
+
+        const normalized = normalizeNonEmptyTaxonomyTerm(entry);
+        if (normalized) {
+          terms.add(normalized);
+        }
+      }
+    } catch {
+      // Invalid JSON: skip
+    }
+  }
+
+  return Array.from(terms).sort();
+}

tests/engine/MetaEngine.test.ts

@@ -372,6 +372,21 @@ describe('MetaEngine', () => {
       const categories = await metaEngine.collectCategoriesFromPosts();
       expect(categories).toEqual(['valid-cat']);
     });
+
+    it('should ignore empty and whitespace-only taxonomy entries from posts', async () => {
+      mockPosts = [
+        {
+          tags: JSON.stringify([' valid-tag ', '', '   ']),
+          categories: JSON.stringify([' valid-cat ', '', '   ']),
+        },
+      ];
+
+      const tags = await metaEngine.collectTagsFromPosts();
+      const categories = await metaEngine.collectCategoriesFromPosts();
+
+      expect(tags).toEqual(['valid-tag']);
+      expect(categories).toEqual(['valid-cat']);
+    });
   });
 
   describe('Event Emission', () => {

tests/engine/TagEngine.test.ts

@@ -634,6 +634,18 @@ describe('TagEngine', () => {
 
       expect(result.discovered).toBeGreaterThanOrEqual(0);
     });
+
+    it('should ignore empty and whitespace-only tags discovered from posts', async () => {
+      mockSelectDataQueue = [
+        [{ tags: '[" valid-tag ", "", "   "]' }],
+        [],
+      ];
+
+      const result = await tagEngine.syncTagsFromPosts();
+
+      expect(result.discovered).toBe(1);
+      expect(result.added).toEqual(['valid-tag']);
+    });
   });
 
   describe('loadTagsFromFile', () => {