feat: tag management

src/main/database/connection.ts

@@ -184,6 +184,18 @@ export class DatabaseConnection {
       CREATE INDEX IF NOT EXISTS idx_post_links_source ON post_links(source_post_id);
       CREATE INDEX IF NOT EXISTS idx_post_links_target ON post_links(target_post_id);
       CREATE UNIQUE INDEX IF NOT EXISTS posts_project_slug_idx ON posts(project_id, slug);
+
+      CREATE TABLE IF NOT EXISTS tags (
+        id TEXT PRIMARY KEY,
+        project_id TEXT NOT NULL,
+        name TEXT NOT NULL,
+        color TEXT,
+        created_at INTEGER NOT NULL,
+        updated_at INTEGER NOT NULL
+      );
+
+      CREATE INDEX IF NOT EXISTS idx_tags_project_id ON tags(project_id);
+      CREATE UNIQUE INDEX IF NOT EXISTS tags_project_name_idx ON tags(project_id, name);
     `);
 
     // Check if project_id column exists in posts table, add if missing (migration)
@@ -368,6 +380,27 @@ export class DatabaseConnection {
       console.log('FTS table migrated - rebuild index required');
     }
 
+    // Migration: Ensure tags table exists (for databases created before tags feature)
+    const tagsTableExists = await this.localClient.execute(
+      "SELECT name FROM sqlite_master WHERE type='table' AND name='tags'"
+    );
+    if (tagsTableExists.rows.length === 0) {
+      console.log('Creating tags table...');
+      await this.localClient.execute(`
+        CREATE TABLE tags (
+          id TEXT PRIMARY KEY,
+          project_id TEXT NOT NULL,
+          name TEXT NOT NULL,
+          color TEXT,
+          created_at INTEGER NOT NULL,
+          updated_at INTEGER NOT NULL
+        )
+      `);
+      await this.localClient.execute('CREATE INDEX idx_tags_project_id ON tags(project_id)');
+      await this.localClient.execute('CREATE UNIQUE INDEX tags_project_name_idx ON tags(project_id, name)');
+      console.log('Tags table created successfully');
+    }
+
     // Create default project if none exists
     const existingProjects = await this.localClient.execute('SELECT COUNT(*) as count FROM projects');
     if (existingProjects.rows[0] && (existingProjects.rows[0].count as number) === 0) {

src/main/database/schema.ts

@@ -95,6 +95,19 @@ export const postLinks = sqliteTable('post_links', {
   createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
 });
 
+// Tags table - stores tag metadata with optional colors
+export const tags = sqliteTable('tags', {
+  id: text('id').primaryKey(),
+  projectId: text('project_id').notNull(),
+  name: text('name').notNull(),
+  color: text('color'), // Optional hex color like #ff0000
+  createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
+  updatedAt: integer('updated_at', { mode: 'timestamp' }).notNull(),
+}, (table) => ({
+  // Composite unique index: tag name must be unique within each project
+  projectNameIdx: uniqueIndex('tags_project_name_idx').on(table.projectId, table.name),
+}));
+
 // Types for TypeScript
 export type Project = typeof projects.$inferSelect;
 export type NewProject = typeof projects.$inferInsert;
@@ -108,3 +121,5 @@ export type Setting = typeof settings.$inferSelect;
 export type NewSetting = typeof settings.$inferInsert;
 export type PostLink = typeof postLinks.$inferSelect;
 export type NewPostLink = typeof postLinks.$inferInsert;
+export type Tag = typeof tags.$inferSelect;
+export type NewTag = typeof tags.$inferInsert;

src/main/engine/TagEngine.ts

@@ -0,0 +1,774 @@
+import { EventEmitter } from 'events';
+import { v4 as uuidv4 } from 'uuid';
+import * as fs from 'fs/promises';
+import * as path from 'path';
+import { app } from 'electron';
+import { getDatabase } from '../database';
+import { taskManager } from './TaskManager';
+
+/**
+ * Tag data stored in the database
+ */
+export interface TagData {
+  id: string;
+  projectId: string;
+  name: string;
+  color?: string;
+  createdAt: Date;
+  updatedAt: Date;
+}
+
+/**
+ * Tag with post count for tag cloud display
+ */
+export interface TagWithCount {
+  name: string;
+  color: string | null;
+  count: number;
+}
+
+/**
+ * Input for creating a new tag
+ */
+export interface CreateTagInput {
+  name: string;
+  color?: string;
+}
+
+/**
+ * Input for updating a tag
+ */
+export interface UpdateTagInput {
+  name?: string;
+  color?: string | null;
+}
+
+/**
+ * Result of tag deletion
+ */
+export interface DeleteTagResult {
+  success: boolean;
+  postsUpdated: number;
+}
+
+/**
+ * Result of merging tags
+ */
+export interface MergeTagsResult {
+  success: boolean;
+  postsUpdated: number;
+  tagsDeleted: number;
+  targetTag: string;
+}
+
+/**
+ * Result of renaming a tag
+ */
+export interface RenameTagResult {
+  success: boolean;
+  postsUpdated: number;
+  oldName: string;
+  newName: string;
+}
+
+/**
+ * Result of syncing tags from posts
+ */
+export interface SyncTagsResult {
+  discovered: number;
+  added: string[];
+}
+
+// Singleton instance
+let tagEngineInstance: TagEngine | null = null;
+
+/**
+ * Get the singleton TagEngine instance
+ */
+export function getTagEngine(): TagEngine {
+  if (!tagEngineInstance) {
+    tagEngineInstance = new TagEngine();
+  }
+  return tagEngineInstance;
+}
+
+/**
+ * Validate hex color format
+ */
+function isValidHexColor(color: string): boolean {
+  return /^#([0-9A-Fa-f]{3}|[0-9A-Fa-f]{6})$/.test(color);
+}
+
+/**
+ * TagEngine manages tag metadata and operations.
+ * 
+ * Tags are stored in a dedicated tags table with optional colors.
+ * This engine handles:
+ * - CRUD operations on tags
+ * - Mass operations (merge, rename) that run as background tasks
+ * - Syncing tags discovered from posts
+ */
+export class TagEngine extends EventEmitter {
+  private currentProjectId: string = 'default';
+
+  constructor() {
+    super();
+  }
+
+  /**
+   * Set the current project context
+   */
+  setProjectContext(projectId: string): void {
+    this.currentProjectId = projectId;
+  }
+
+  /**
+   * Get the current project context
+   */
+  getProjectContext(): string {
+    return this.currentProjectId;
+  }
+
+  /**
+   * Get the tags file path for filesystem persistence
+   */
+  private getTagsFilePath(): string {
+    const userDataPath = app.getPath('userData');
+    return path.join(userDataPath, 'projects', this.currentProjectId, 'meta', 'tags-metadata.json');
+  }
+
+  /**
+   * Get all tags with their post counts for the tag cloud
+   */
+  async getTagsWithCounts(): Promise<TagWithCount[]> {
+    const client = getDatabase().getLocalClient();
+    if (!client) return [];
+
+    // Query tags with counts from posts
+    // Use a subquery to count posts per tag name
+    const result = await client.execute({
+      sql: `
+        SELECT 
+          t.name,
+          t.color,
+          COALESCE(pc.post_count, 0) as post_count
+        FROM tags t
+        LEFT JOIN (
+          SELECT je.value as tag_name, COUNT(DISTINCT p.id) as post_count
+          FROM posts p, json_each(p.tags) je
+          WHERE p.project_id = ?
+          GROUP BY je.value
+        ) pc ON LOWER(pc.tag_name) = LOWER(t.name)
+        WHERE t.project_id = ?
+        ORDER BY post_count DESC, t.name ASC
+      `,
+      args: [this.currentProjectId, this.currentProjectId],
+    });
+
+    return result.rows.map((row: any) => ({
+      name: row.name as string,
+      color: row.color as string | null,
+      count: Number(row.post_count) || 0,
+    }));
+  }
+
+  /**
+   * Create a new tag
+   */
+  async createTag(input: CreateTagInput): Promise<TagData> {
+    const client = getDatabase().getLocalClient();
+    if (!client) throw new Error('Database not initialized');
+
+    const name = input.name.trim().toLowerCase();
+    if (!name) {
+      throw new Error('Tag name is required');
+    }
+
+    // Validate color if provided
+    if (input.color && !isValidHexColor(input.color)) {
+      throw new Error('Invalid color format. Use hex format like #ff0000 or #f00');
+    }
+
+    // Check for duplicate
+    const existing = await client.execute({
+      sql: 'SELECT id, name FROM tags WHERE project_id = ? AND LOWER(name) = LOWER(?)',
+      args: [this.currentProjectId, name],
+    });
+
+    if (existing.rows.length > 0) {
+      throw new Error(`Tag "${name}" already exists`);
+    }
+
+    const now = Date.now();
+    const tag: TagData = {
+      id: uuidv4(),
+      projectId: this.currentProjectId,
+      name,
+      color: input.color,
+      createdAt: new Date(now),
+      updatedAt: new Date(now),
+    };
+
+    await client.execute({
+      sql: 'INSERT INTO tags (id, project_id, name, color, created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?)',
+      args: [tag.id, tag.projectId, tag.name, tag.color || null, now, now],
+    });
+
+    this.emit('tagCreated', tag);
+    await this.saveTagsToFile();
+
+    return tag;
+  }
+
+  /**
+   * Update a tag
+   */
+  async updateTag(id: string, input: UpdateTagInput): Promise<TagData | null> {
+    const client = getDatabase().getLocalClient();
+    if (!client) return null;
+
+    // Get existing tag
+    const existing = await client.execute({
+      sql: 'SELECT * FROM tags WHERE id = ? AND project_id = ?',
+      args: [id, this.currentProjectId],
+    });
+
+    if (existing.rows.length === 0) {
+      return null;
+    }
+
+    const row = existing.rows[0] as any;
+
+    // Validate color if provided
+    if (input.color !== undefined && input.color !== null && !isValidHexColor(input.color)) {
+      throw new Error('Invalid color format. Use hex format like #ff0000 or #f00');
+    }
+
+    const now = Date.now();
+    const updates: string[] = [];
+    const args: any[] = [];
+
+    if (input.color !== undefined) {
+      updates.push('color = ?');
+      args.push(input.color);
+    }
+
+    if (updates.length === 0) {
+      // No updates
+      return this.rowToTagData(row);
+    }
+
+    updates.push('updated_at = ?');
+    args.push(now);
+    args.push(id);
+    args.push(this.currentProjectId);
+
+    await client.execute({
+      sql: `UPDATE tags SET ${updates.join(', ')} WHERE id = ? AND project_id = ?`,
+      args,
+    });
+
+    const updatedTag: TagData = {
+      id: row.id,
+      projectId: row.project_id,
+      name: row.name,
+      color: input.color !== undefined ? input.color || undefined : row.color,
+      createdAt: new Date(row.created_at),
+      updatedAt: new Date(now),
+    };
+
+    this.emit('tagUpdated', updatedTag);
+    await this.saveTagsToFile();
+
+    return updatedTag;
+  }
+
+  /**
+   * Delete a tag and remove it from all posts (runs as background task)
+   */
+  async deleteTag(id: string): Promise<DeleteTagResult> {
+    const client = getDatabase().getLocalClient();
+    if (!client) throw new Error('Database not initialized');
+
+    // Get tag
+    const tagResult = await client.execute({
+      sql: 'SELECT * FROM tags WHERE id = ? AND project_id = ?',
+      args: [id, this.currentProjectId],
+    });
+
+    if (tagResult.rows.length === 0) {
+      throw new Error('Tag not found');
+    }
+
+    const tag = tagResult.rows[0] as any;
+    const tagName = tag.name as string;
+
+    // Run the deletion as a background task
+    return taskManager.runTask({
+      id: `delete-tag-${id}-${Date.now()}`,
+      name: `Delete tag "${tagName}"`,
+      execute: async (onProgress) => {
+        onProgress(0, `Finding posts with tag "${tagName}"...`);
+
+        // Find all posts with this tag
+        const postsResult = await client.execute({
+          sql: `SELECT id, tags FROM posts WHERE project_id = ? AND tags LIKE ?`,
+          args: [this.currentProjectId, `%"${tagName}"%`],
+        });
+
+        const postsToUpdate = postsResult.rows.filter((row: any) => {
+          const tags: string[] = JSON.parse(row.tags || '[]');
+          return tags.includes(tagName);
+        });
+
+        const total = postsToUpdate.length;
+        let updated = 0;
+
+        for (const row of postsToUpdate) {
+          const postId = row.id as string;
+          const tags: string[] = JSON.parse((row as any).tags || '[]');
+          const newTags = tags.filter(t => t !== tagName);
+
+          await client.execute({
+            sql: 'UPDATE posts SET tags = ?, updated_at = ? WHERE id = ?',
+            args: [JSON.stringify(newTags), Date.now(), postId],
+          });
+
+          updated++;
+          onProgress((updated / total) * 80, `Updated ${updated}/${total} posts...`);
+        }
+
+        onProgress(90, 'Deleting tag...');
+
+        // Delete the tag
+        await client.execute({
+          sql: 'DELETE FROM tags WHERE id = ? AND project_id = ?',
+          args: [id, this.currentProjectId],
+        });
+
+        onProgress(100, 'Complete');
+
+        this.emit('tagDeleted', id);
+        await this.saveTagsToFile();
+
+        return { success: true, postsUpdated: updated };
+      },
+    });
+  }
+
+  /**
+   * Merge multiple source tags into a target tag (runs as background task)
+   */
+  async mergeTags(sourceTagIds: string[], targetTagId: string): Promise<MergeTagsResult> {
+    const client = getDatabase().getLocalClient();
+    if (!client) throw new Error('Database not initialized');
+
+    if (sourceTagIds.length === 0) {
+      throw new Error('Source tags are required');
+    }
+
+    // Verify all source tags exist
+    const sourceTags: any[] = [];
+    for (const id of sourceTagIds) {
+      const result = await client.execute({
+        sql: 'SELECT * FROM tags WHERE id = ? AND project_id = ?',
+        args: [id, this.currentProjectId],
+      });
+      if (result.rows.length > 0) {
+        sourceTags.push(result.rows[0]);
+      }
+    }
+
+    // Verify target tag exists
+    const targetResult = await client.execute({
+      sql: 'SELECT * FROM tags WHERE id = ? AND project_id = ?',
+      args: [targetTagId, this.currentProjectId],
+    });
+
+    if (targetResult.rows.length === 0) {
+      throw new Error('Target tag not found');
+    }
+
+    const targetTag = targetResult.rows[0] as any;
+    const targetName = targetTag.name as string;
+    const sourceNames = sourceTags.map((t: any) => t.name as string);
+
+    // Run as background task
+    return taskManager.runTask({
+      id: `merge-tags-${Date.now()}`,
+      name: `Merge tags into "${targetName}"`,
+      execute: async (onProgress) => {
+        onProgress(0, 'Finding posts to update...');
+
+        let totalPostsUpdated = 0;
+
+        // For each source tag, update posts and delete the tag
+        for (let i = 0; i < sourceNames.length; i++) {
+          const sourceName = sourceNames[i];
+          onProgress((i / sourceNames.length) * 80, `Processing tag "${sourceName}"...`);
+
+          // Find posts with this source tag
+          const postsResult = await client.execute({
+            sql: `SELECT id, tags FROM posts WHERE project_id = ? AND tags LIKE ?`,
+            args: [this.currentProjectId, `%"${sourceName}"%`],
+          });
+
+          for (const row of postsResult.rows) {
+            const postId = row.id as string;
+            const tags: string[] = JSON.parse((row as any).tags || '[]');
+            
+            if (tags.includes(sourceName)) {
+              // Remove source tag and add target if not already present
+              const newTags = tags.filter(t => t !== sourceName);
+              if (!newTags.includes(targetName)) {
+                newTags.push(targetName);
+              }
+
+              await client.execute({
+                sql: 'UPDATE posts SET tags = ?, updated_at = ? WHERE id = ?',
+                args: [JSON.stringify(newTags), Date.now(), postId],
+              });
+
+              totalPostsUpdated++;
+            }
+          }
+        }
+
+        onProgress(90, 'Deleting source tags...');
+
+        // Delete source tags
+        for (const id of sourceTagIds) {
+          await client.execute({
+            sql: 'DELETE FROM tags WHERE id = ? AND project_id = ?',
+            args: [id, this.currentProjectId],
+          });
+        }
+
+        onProgress(100, 'Complete');
+
+        const result: MergeTagsResult = {
+          success: true,
+          postsUpdated: totalPostsUpdated,
+          tagsDeleted: sourceTagIds.length,
+          targetTag: targetName,
+        };
+
+        this.emit('tagsMerged', result);
+        await this.saveTagsToFile();
+
+        return result;
+      },
+    });
+  }
+
+  /**
+   * Rename a tag (runs as background task to update posts)
+   */
+  async renameTag(id: string, newName: string): Promise<RenameTagResult> {
+    const client = getDatabase().getLocalClient();
+    if (!client) throw new Error('Database not initialized');
+
+    newName = newName.trim().toLowerCase();
+    if (!newName) {
+      throw new Error('New name is required');
+    }
+
+    // Get existing tag
+    const tagResult = await client.execute({
+      sql: 'SELECT * FROM tags WHERE id = ? AND project_id = ?',
+      args: [id, this.currentProjectId],
+    });
+
+    if (tagResult.rows.length === 0) {
+      throw new Error('Tag not found');
+    }
+
+    const tag = tagResult.rows[0] as any;
+    const oldName = tag.name as string;
+
+    if (oldName === newName) {
+      return { success: true, postsUpdated: 0, oldName, newName };
+    }
+
+    // Check for duplicate
+    const duplicateResult = await client.execute({
+      sql: 'SELECT id FROM tags WHERE project_id = ? AND LOWER(name) = LOWER(?) AND id != ?',
+      args: [this.currentProjectId, newName, id],
+    });
+
+    if (duplicateResult.rows.length > 0) {
+      throw new Error(`Tag "${newName}" already exists`);
+    }
+
+    // Run as background task
+    return taskManager.runTask({
+      id: `rename-tag-${id}-${Date.now()}`,
+      name: `Rename tag "${oldName}" to "${newName}"`,
+      execute: async (onProgress) => {
+        onProgress(0, 'Finding posts to update...');
+
+        // Find posts with this tag
+        const postsResult = await client.execute({
+          sql: `SELECT id, tags FROM posts WHERE project_id = ? AND tags LIKE ?`,
+          args: [this.currentProjectId, `%"${oldName}"%`],
+        });
+
+        const postsToUpdate = postsResult.rows.filter((row: any) => {
+          const tags: string[] = JSON.parse(row.tags || '[]');
+          return tags.includes(oldName);
+        });
+
+        const total = postsToUpdate.length;
+        let updated = 0;
+
+        for (const row of postsToUpdate) {
+          const postId = row.id as string;
+          const tags: string[] = JSON.parse((row as any).tags || '[]');
+          const newTags = tags.map(t => t === oldName ? newName : t);
+
+          await client.execute({
+            sql: 'UPDATE posts SET tags = ?, updated_at = ? WHERE id = ?',
+            args: [JSON.stringify(newTags), Date.now(), postId],
+          });
+
+          updated++;
+          onProgress((updated / total) * 80, `Updated ${updated}/${total} posts...`);
+        }
+
+        onProgress(90, 'Updating tag record...');
+
+        // Update the tag name
+        await client.execute({
+          sql: 'UPDATE tags SET name = ?, updated_at = ? WHERE id = ? AND project_id = ?',
+          args: [newName, Date.now(), id, this.currentProjectId],
+        });
+
+        onProgress(100, 'Complete');
+
+        const result: RenameTagResult = {
+          success: true,
+          postsUpdated: updated,
+          oldName,
+          newName,
+        };
+
+        this.emit('tagRenamed', result);
+        await this.saveTagsToFile();
+
+        return result;
+      },
+    });
+  }
+
+  /**
+   * Get a tag by ID
+   */
+  async getTag(id: string): Promise<TagData | null> {
+    const client = getDatabase().getLocalClient();
+    if (!client) return null;
+
+    const result = await client.execute({
+      sql: 'SELECT * FROM tags WHERE id = ? AND project_id = ?',
+      args: [id, this.currentProjectId],
+    });
+
+    if (result.rows.length === 0) {
+      return null;
+    }
+
+    return this.rowToTagData(result.rows[0] as any);
+  }
+
+  /**
+   * Get a tag by name (case-insensitive)
+   */
+  async getTagByName(name: string): Promise<TagData | null> {
+    const client = getDatabase().getLocalClient();
+    if (!client) return null;
+
+    const result = await client.execute({
+      sql: 'SELECT * FROM tags WHERE project_id = ? AND LOWER(name) = LOWER(?)',
+      args: [this.currentProjectId, name.trim().toLowerCase()],
+    });
+
+    if (result.rows.length === 0) {
+      return null;
+    }
+
+    return this.rowToTagData(result.rows[0] as any);
+  }
+
+  /**
+   * Get all tags for the current project
+   */
+  async getAllTags(): Promise<TagData[]> {
+    const client = getDatabase().getLocalClient();
+    if (!client) return [];
+
+    const result = await client.execute({
+      sql: 'SELECT * FROM tags WHERE project_id = ? ORDER BY name ASC',
+      args: [this.currentProjectId],
+    });
+
+    return result.rows.map((row: any) => this.rowToTagData(row));
+  }
+
+  /**
+   * Get post IDs that have a specific tag
+   */
+  async getPostsWithTag(tagId: string): Promise<string[]> {
+    const client = getDatabase().getLocalClient();
+    if (!client) return [];
+
+    // First get the tag name
+    const tagResult = await client.execute({
+      sql: 'SELECT name FROM tags WHERE id = ? AND project_id = ?',
+      args: [tagId, this.currentProjectId],
+    });
+
+    if (tagResult.rows.length === 0) {
+      return [];
+    }
+
+    const tagName = (tagResult.rows[0] as any).name as string;
+
+    // Find posts with this tag
+    const postsResult = await client.execute({
+      sql: `SELECT id, tags FROM posts WHERE project_id = ? AND tags LIKE ?`,
+      args: [this.currentProjectId, `%"${tagName}"%`],
+    });
+
+    return postsResult.rows
+      .filter((row: any) => {
+        const tags: string[] = JSON.parse(row.tags || '[]');
+        return tags.includes(tagName);
+      })
+      .map((row: any) => row.id as string);
+  }
+
+  /**
+   * Sync tags from existing posts - discover tags that exist in posts but not in tags table
+   */
+  async syncTagsFromPosts(): Promise<SyncTagsResult> {
+    const client = getDatabase().getLocalClient();
+    if (!client) throw new Error('Database not initialized');
+
+    // Get all tags from posts
+    const postsResult = await client.execute({
+      sql: 'SELECT tags FROM posts WHERE project_id = ?',
+      args: [this.currentProjectId],
+    });
+
+    const discoveredTags = new Set<string>();
+    for (const row of postsResult.rows) {
+      const tags: string[] = JSON.parse((row as any).tags || '[]');
+      for (const tag of tags) {
+        if (tag.trim()) {
+          discoveredTags.add(tag.trim().toLowerCase());
+        }
+      }
+    }
+
+    // Get existing tags
+    const existingResult = await client.execute({
+      sql: 'SELECT name FROM tags WHERE project_id = ?',
+      args: [this.currentProjectId],
+    });
+
+    const existingNames = new Set(existingResult.rows.map((row: any) => (row.name as string).toLowerCase()));
+
+    // Find missing tags
+    const missingTags = Array.from(discoveredTags).filter(t => !existingNames.has(t));
+    const added: string[] = [];
+
+    // Add missing tags
+    const now = Date.now();
+    for (const tagName of missingTags) {
+      await client.execute({
+        sql: 'INSERT INTO tags (id, project_id, name, color, created_at, updated_at) VALUES (?, ?, ?, NULL, ?, ?)',
+        args: [uuidv4(), this.currentProjectId, tagName, now, now],
+      });
+      added.push(tagName);
+    }
+
+    if (added.length > 0) {
+      this.emit('tagsSynced', { discovered: discoveredTags.size, added });
+      await this.saveTagsToFile();
+    }
+
+    return {
+      discovered: discoveredTags.size,
+      added,
+    };
+  }
+
+  /**
+   * Convert database row to TagData
+   */
+  private rowToTagData(row: any): TagData {
+    return {
+      id: row.id,
+      projectId: row.project_id,
+      name: row.name,
+      color: row.color || undefined,
+      createdAt: new Date(row.created_at),
+      updatedAt: new Date(row.updated_at),
+    };
+  }
+
+  /**
+   * Save tags metadata to filesystem for sync
+   */
+  private async saveTagsToFile(): Promise<void> {
+    try {
+      const tags = await this.getAllTags();
+      const filePath = this.getTagsFilePath();
+      const dir = path.dirname(filePath);
+
+      await fs.mkdir(dir, { recursive: true });
+      await fs.writeFile(filePath, JSON.stringify(tags, null, 2), 'utf-8');
+    } catch (error) {
+      console.error('[TagEngine] Failed to save tags to file:', error);
+    }
+  }
+
+  /**
+   * Load tags from filesystem (for initial sync)
+   */
+  async loadTagsFromFile(): Promise<void> {
+    try {
+      const filePath = this.getTagsFilePath();
+      const content = await fs.readFile(filePath, 'utf-8');
+      const tags: TagData[] = JSON.parse(content);
+
+      const client = getDatabase().getLocalClient();
+      if (!client) return;
+
+      for (const tag of tags) {
+        // Check if tag exists
+        const existing = await client.execute({
+          sql: 'SELECT id FROM tags WHERE id = ? AND project_id = ?',
+          args: [tag.id, this.currentProjectId],
+        });
+
+        if (existing.rows.length === 0) {
+          await client.execute({
+            sql: 'INSERT INTO tags (id, project_id, name, color, created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?)',
+            args: [
+              tag.id,
+              this.currentProjectId,
+              tag.name,
+              tag.color || null,
+              tag.createdAt instanceof Date ? tag.createdAt.getTime() : tag.createdAt,
+              tag.updatedAt instanceof Date ? tag.updatedAt.getTime() : tag.updatedAt,
+            ],
+          });
+        }
+      }
+    } catch (error: any) {
+      if (error.code !== 'ENOENT') {
+        console.error('[TagEngine] Failed to load tags from file:', error);
+      }
+    }
+  }
+}

src/main/engine/index.ts

@@ -4,6 +4,18 @@ export { MediaEngine, getMediaEngine, type MediaData } from './MediaEngine';
 export { SyncEngine, getSyncEngine, type SyncConfig, type SyncResult, type SyncDirection, type SyncStatus } from './SyncEngine';
 export { ProjectEngine, getProjectEngine, type ProjectData } from './ProjectEngine';
 export { MetaEngine, getMetaEngine, type ProjectMetadata, DEFAULT_CATEGORIES } from './MetaEngine';
+export {
+  TagEngine,
+  getTagEngine,
+  type TagData,
+  type TagWithCount,
+  type CreateTagInput,
+  type UpdateTagInput,
+  type DeleteTagResult,
+  type MergeTagsResult,
+  type RenameTagResult,
+  type SyncTagsResult,
+} from './TagEngine';
 export {
   stemText,
   stemWord,
@@ -25,3 +37,4 @@ export {
   type FileDownloadResult,
   type ConflictResolution,
 } from './DropboxSyncEngine';
+

src/main/ipc/handlers.ts

@@ -6,6 +6,7 @@ import { getSyncEngine, SyncConfig, SyncDirection } from '../engine/SyncEngine';
 import { getDropboxSyncEngine, DropboxSyncConfig, ConflictResolution } from '../engine/DropboxSyncEngine';
 import { getProjectEngine, ProjectData } from '../engine/ProjectEngine';
 import { getMetaEngine } from '../engine/MetaEngine';
+import { getTagEngine } from '../engine/TagEngine';
 import { taskManager, TaskProgress } from '../engine/TaskManager';
 import { getDatabase } from '../database';
 import { media } from '../database/schema';
@@ -52,9 +53,11 @@ export function registerIpcHandlers(): void {
       const postEngine = getPostEngine();
       const mediaEngine = getMediaEngine();
       const metaEngine = getMetaEngine();
+      const tagEngine = getTagEngine();
       postEngine.setProjectContext(project.id);
       mediaEngine.setProjectContext(project.id);
       metaEngine.setProjectContext(project.id);
+      tagEngine.setProjectContext(project.id);
       
       // Sync meta on startup
       await metaEngine.syncOnStartup();
@@ -72,9 +75,11 @@ export function registerIpcHandlers(): void {
       const postEngine = getPostEngine();
       const mediaEngine = getMediaEngine();
       const metaEngine = getMetaEngine();
+      const tagEngine = getTagEngine();
       postEngine.setProjectContext(project.id);
       mediaEngine.setProjectContext(project.id);
       metaEngine.setProjectContext(project.id);
+      tagEngine.setProjectContext(project.id);
       
       // Sync meta on project switch
       await metaEngine.syncOnStartup();
@@ -549,6 +554,63 @@ export function registerIpcHandlers(): void {
     return engine.getProjectMetadata();
   });
 
+  // ============ Tag Management Handlers ============
+
+  ipcMain.handle('tags:getAll', async () => {
+    const engine = getTagEngine();
+    return engine.getAllTags();
+  });
+
+  ipcMain.handle('tags:getWithCounts', async () => {
+    const engine = getTagEngine();
+    return engine.getTagsWithCounts();
+  });
+
+  ipcMain.handle('tags:get', async (_, id: string) => {
+    const engine = getTagEngine();
+    return engine.getTag(id);
+  });
+
+  ipcMain.handle('tags:getByName', async (_, name: string) => {
+    const engine = getTagEngine();
+    return engine.getTagByName(name);
+  });
+
+  ipcMain.handle('tags:create', async (_, data: { name: string; color?: string }) => {
+    const engine = getTagEngine();
+    return engine.createTag(data);
+  });
+
+  ipcMain.handle('tags:update', async (_, id: string, data: { name?: string; color?: string | null }) => {
+    const engine = getTagEngine();
+    return engine.updateTag(id, data);
+  });
+
+  ipcMain.handle('tags:delete', async (_, id: string) => {
+    const engine = getTagEngine();
+    return engine.deleteTag(id);
+  });
+
+  ipcMain.handle('tags:merge', async (_, sourceTagIds: string[], targetTagId: string) => {
+    const engine = getTagEngine();
+    return engine.mergeTags(sourceTagIds, targetTagId);
+  });
+
+  ipcMain.handle('tags:rename', async (_, id: string, newName: string) => {
+    const engine = getTagEngine();
+    return engine.renameTag(id, newName);
+  });
+
+  ipcMain.handle('tags:getPostsWithTag', async (_, tagId: string) => {
+    const engine = getTagEngine();
+    return engine.getPostsWithTag(tagId);
+  });
+
+  ipcMain.handle('tags:syncFromPosts', async () => {
+    const engine = getTagEngine();
+    return engine.syncTagsFromPosts();
+  });
+
   // ============ Event Forwarding ============
   
   // Forward engine events to renderer
@@ -557,6 +619,7 @@ export function registerIpcHandlers(): void {
   const syncEngine = getSyncEngine();
   const projectEngine = getProjectEngine();
   const metaEngine = getMetaEngine();
+  const tagEngine = getTagEngine();
 
   const forwardEvent = (eventName: string) => {
     return (...args: unknown[]) => {
@@ -586,6 +649,13 @@ export function registerIpcHandlers(): void {
   metaEngine.on('categoriesChanged', forwardEvent('meta:categoriesChanged'));
   metaEngine.on('projectMetadataChanged', forwardEvent('meta:projectMetadataChanged'));
 
+  tagEngine.on('tagCreated', forwardEvent('tag:created'));
+  tagEngine.on('tagUpdated', forwardEvent('tag:updated'));
+  tagEngine.on('tagDeleted', forwardEvent('tag:deleted'));
+  tagEngine.on('tagRenamed', forwardEvent('tag:renamed'));
+  tagEngine.on('tagsMerged', forwardEvent('tags:merged'));
+  tagEngine.on('tagsSynced', forwardEvent('tags:synced'));
+
   syncEngine.on('syncStarted', forwardEvent('sync:started'));
   syncEngine.on('syncCompleted', forwardEvent('sync:completed'));
   syncEngine.on('syncFailed', forwardEvent('sync:failed'));

src/main/preload.ts

@@ -115,6 +115,21 @@ contextBridge.exposeInMainWorld('electronAPI', {
     updateProjectMetadata: (updates: { name?: string; description?: string }) => ipcRenderer.invoke('meta:updateProjectMetadata', updates),
   },
 
+  // Tag Management (advanced tag operations)
+  tags: {
+    getAll: () => ipcRenderer.invoke('tags:getAll'),
+    getWithCounts: () => ipcRenderer.invoke('tags:getWithCounts'),
+    get: (id: string) => ipcRenderer.invoke('tags:get', id),
+    getByName: (name: string) => ipcRenderer.invoke('tags:getByName', name),
+    create: (data: { name: string; color?: string }) => ipcRenderer.invoke('tags:create', data),
+    update: (id: string, data: { name?: string; color?: string | null }) => ipcRenderer.invoke('tags:update', id, data),
+    delete: (id: string) => ipcRenderer.invoke('tags:delete', id),
+    merge: (sourceTagIds: string[], targetTagId: string) => ipcRenderer.invoke('tags:merge', sourceTagIds, targetTagId),
+    rename: (id: string, newName: string) => ipcRenderer.invoke('tags:rename', id, newName),
+    getPostsWithTag: (tagId: string) => ipcRenderer.invoke('tags:getPostsWithTag', tagId),
+    syncFromPosts: () => ipcRenderer.invoke('tags:syncFromPosts'),
+  },
+
   // Event listeners
   on: (channel: string, callback: (...args: unknown[]) => void) => {
     const subscription = (_event: Electron.IpcRendererEvent, ...args: unknown[]) => callback(...args);

src/renderer/components/ActivityBar/ActivityBar.tsx

@@ -22,6 +22,12 @@ const SettingsIcon = () => (
   </svg>
 );
 
+const TagsIcon = () => (
+  <svg width="24" height="24" viewBox="0 0 24 24" fill="currentColor">
+    <path d="M21.41 11.58l-9-9C12.05 2.22 11.55 2 11 2H4c-1.1 0-2 .9-2 2v7c0 .55.22 1.05.59 1.42l9 9c.36.36.86.58 1.41.58s1.05-.22 1.41-.59l7-7c.37-.36.59-.86.59-1.41s-.23-1.06-.59-1.42zM5.5 7C4.67 7 4 6.33 4 5.5S4.67 4 5.5 4 7 4.67 7 5.5 6.33 7 5.5 7z"/>
+  </svg>
+);
+
 const SyncIcon = () => (
   <svg width="24" height="24" viewBox="0 0 24 24" fill="currentColor">
     <path d="M12 4V1L8 5l4 4V6c3.31 0 6 2.69 6 6 0 1.01-.25 1.97-.7 2.8l1.46 1.46C19.54 15.03 20 13.57 20 12c0-4.42-3.58-8-8-8zm0 14c-3.31 0-6-2.69-6-6 0-1.01.25-1.97.7-2.8L5.24 7.74C4.46 8.97 4 10.43 4 12c0 4.42 3.58 8 8 8v3l4-4-4-4v3z"/>
@@ -35,12 +41,20 @@ export const ActivityBar: React.FC = () => {
   
   // Check if settings tab is currently active
   const isSettingsTabActive = tabs.some(t => t.type === 'settings' && t.id === activeTabId);
+  
+  // Check if tags tab is currently active
+  const isTagsTabActive = tabs.some(t => t.type === 'tags' && t.id === activeTabId);
 
   const handleSettingsClick = () => {
     // Open settings as a dedicated (non-transient) tab
     openTab({ type: 'settings', id: 'settings', isTransient: false });
   };
 
+  const handleTagsClick = () => {
+    // Open tags as a dedicated (non-transient) tab
+    openTab({ type: 'tags', id: 'tags', isTransient: false });
+  };
+
   return (
     <div className="activity-bar">
       <div className="activity-bar-top">
@@ -58,6 +72,13 @@ export const ActivityBar: React.FC = () => {
         >
           <MediaIcon />
         </button>
+        <button
+          className={`activity-bar-item ${isTagsTabActive ? 'active' : ''}`}
+          onClick={handleTagsClick}
+          title="Tags"
+        >
+          <TagsIcon />
+        </button>
       </div>
       
       <div className="activity-bar-bottom">

src/renderer/components/Editor/Editor.tsx

@@ -7,6 +7,7 @@ import { Lightbox, useMarkdownImages } from '../Lightbox';
 import { PostLinks } from '../PostLinks';
 import { ErrorModal } from '../ErrorModal';
 import { SettingsView } from '../SettingsView';
+import { TagsView } from '../TagsView';
 import { AutoSaveManager } from '../../utils';
 import './Editor.css';
 
@@ -1029,6 +1030,7 @@ export const Editor: React.FC = () => {
   const showPost = activeTab?.type === 'post';
   const showMedia = activeTab?.type === 'media';
   const showSettings = activeTab?.type === 'settings' || (activeView === 'settings' && !activeTab);
+  const showTags = activeTab?.type === 'tags' || (activeView === 'tags' && !activeTab);
 
   // Clear selectedPostId if the post doesn't exist (e.g., after project switch)
   useEffect(() => {
@@ -1082,6 +1084,16 @@ export const Editor: React.FC = () => {
     );
   }
 
+  // Show tags if tags tab is active
+  if (showTags) {
+    return (
+      <>
+        <TagsView />
+        {renderErrorModal()}
+      </>
+    );
+  }
+
   // Show post editor if a post tab is active
   if (showPost && activeTabId) {
     const post = posts.find(p => p.id === activeTabId);

src/renderer/components/Sidebar/Sidebar.tsx

@@ -636,6 +636,50 @@ const MediaList: React.FC = () => {
 };
 
 import { scrollToSettingsSection, SettingsCategory } from '../SettingsView/SettingsView';
+import { scrollToTagsSection, TagsCategory } from '../TagsView';
+
+const TagsNav: React.FC = () => {
+  const [activeSection, setActiveSection] = useState<TagsCategory | null>(null);
+
+  const handleNavClick = (category: TagsCategory) => {
+    setActiveSection(category);
+    scrollToTagsSection(category);
+  };
+
+  return (
+    <div className="sidebar-content settings-panel">
+      <div className="sidebar-section">
+        <div className="sidebar-section-header">
+          <span>TAGS</span>
+        </div>
+      </div>
+
+      <div className="settings-nav-list">
+        <button
+          className={`settings-nav-entry ${activeSection === 'cloud' ? 'active' : ''}`}
+          onClick={() => handleNavClick('cloud')}
+        >
+          <span className="settings-nav-entry-icon">☁️</span>
+          <span>Tag Cloud</span>
+        </button>
+        <button
+          className={`settings-nav-entry ${activeSection === 'manage' ? 'active' : ''}`}
+          onClick={() => handleNavClick('manage')}
+        >
+          <span className="settings-nav-entry-icon">✏️</span>
+          <span>Create & Edit</span>
+        </button>
+        <button 
+          className={`settings-nav-entry ${activeSection === 'merge' ? 'active' : ''}`}
+          onClick={() => handleNavClick('merge')}
+        >
+          <span className="settings-nav-entry-icon">🔀</span>
+          <span>Merge Tags</span>
+        </button>
+      </div>
+    </div>
+  );
+};
 
 const SettingsNav: React.FC = () => {
   const { syncConfigured } = useAppStore();
@@ -715,6 +759,7 @@ export const Sidebar: React.FC = () => {
       {activeView === 'posts' && <PostsList />}
       {activeView === 'media' && <MediaList />}
       {activeView === 'settings' && <SettingsNav />}
+      {activeView === 'tags' && <TagsNav />}
     </div>
   );
 };

src/renderer/components/TabBar/TabBar.tsx

@@ -7,6 +7,10 @@ const getTabTitle = (tab: Tab, posts: { id: string; title: string }[], media: {
     return 'Settings';
   }
   
+  if (tab.type === 'tags') {
+    return 'Tags';
+  }
+  
   if (tab.type === 'post') {
     const post = posts.find(p => p.id === tab.id);
     return post?.title || 'Untitled';
@@ -40,6 +44,12 @@ const getTabIcon = (tab: Tab): React.ReactNode => {
           <path d="M9.1 4.4L8.6 2H7.4l-.5 2.4-.7.3-2-1.3-.9.8 1.3 2-.2.7-2.4.5v1.2l2.4.5.3.8-1.3 2 .8.8 2-1.3.8.3.4 2.3h1.2l.5-2.4.8-.3 2 1.3.8-.8-1.3-2 .3-.8 2.3-.4V7.4l-2.4-.5-.3-.8 1.3-2-.8-.8-2 1.3-.7-.2zM9.4 1l.5 2.4L12 2.1l2 2-1.4 2.1 2.4.4v3l-2.4.5L14 12l-2 2-2.1-1.4-.5 2.4h-3L5.9 12.5 4 14l-2-2 1.4-2.1L1 9.4v-3l2.4-.5L2 4l2-2 2.1 1.4.4-2.4h3zm.6 7c0 1.1-.9 2-2 2s-2-.9-2-2 .9-2 2-2 2 .9 2 2zM8 9c.6 0 1-.4 1-1s-.4-1-1-1-1 .4-1 1 .4 1 1 1z"/>
         </svg>
       );
+    case 'tags':
+      return (
+        <svg width="16" height="16" viewBox="0 0 16 16" fill="currentColor">
+          <path d="M14.28 7.72l-6-6A1 1 0 007.57 1.5H2.5A1 1 0 001.5 2.5v5.07a1 1 0 00.22.56l6 6a1 1 0 001.41 0l5.15-5a1 1 0 000-1.41zM4 5a1 1 0 110-2 1 1 0 010 2z"/>
+        </svg>
+      );
     default:
       return (
         <svg width="16" height="16" viewBox="0 0 16 16" fill="currentColor">

src/renderer/components/TagsView/TagsView.css

@@ -0,0 +1,366 @@
+.tags-view {
+  height: 100%;
+  overflow-y: auto;
+  padding: 24px;
+  background-color: var(--background-primary);
+}
+
+.tags-view-header {
+  margin-bottom: 32px;
+}
+
+.tags-view-header h2 {
+  margin: 0 0 8px 0;
+  font-size: 1.75rem;
+  font-weight: 600;
+  color: var(--text-primary);
+}
+
+.tags-view-content {
+  max-width: 900px;
+}
+
+/* Text utilities */
+.text-muted {
+  color: var(--text-secondary);
+}
+
+.text-small {
+  font-size: 0.85rem;
+}
+
+/* Section */
+.tags-section {
+  margin-bottom: 40px;
+  padding-top: 8px;
+}
+
+.tags-section-header {
+  margin-bottom: 16px;
+}
+
+.tags-section-header h3 {
+  margin: 0 0 4px 0;
+  font-size: 1.25rem;
+  font-weight: 600;
+  color: var(--text-primary);
+}
+
+.tags-section-description {
+  margin: 0;
+  color: var(--text-secondary);
+  font-size: 0.9rem;
+}
+
+.tags-section-content {
+  padding: 16px;
+  background-color: var(--background-secondary);
+  border-radius: 8px;
+  border: 1px solid var(--border-color);
+}
+
+/* Loading and Empty States */
+.tags-loading,
+.tags-empty {
+  padding: 40px;
+  text-align: center;
+  color: var(--text-secondary);
+}
+
+.tags-empty button {
+  margin-top: 16px;
+}
+
+/* Tag Cloud */
+.tag-cloud {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 10px;
+  align-items: center;
+  padding: 8px;
+}
+
+.tag-cloud-item {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  padding: 6px 12px;
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  background: var(--background-primary);
+  color: var(--text-primary);
+  cursor: pointer;
+  transition: all 0.15s ease;
+  font-family: inherit;
+}
+
+.tag-cloud-item:hover {
+  border-color: var(--accent-color);
+  background: var(--background-hover);
+}
+
+.tag-cloud-item.selected {
+  border-color: var(--accent-color);
+  background: var(--accent-color-transparent);
+  box-shadow: 0 0 0 2px var(--accent-color-transparent);
+}
+
+.tag-cloud-item.has-color {
+  border: none;
+  padding: 7px 13px;
+  border-radius: 16px;
+}
+
+.tag-cloud-item.has-color:hover {
+  opacity: 0.9;
+}
+
+.tag-cloud-item.has-color.selected {
+  box-shadow: 0 0 0 3px var(--accent-color);
+}
+
+.tag-count {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 20px;
+  height: 20px;
+  padding: 0 6px;
+  font-size: 0.7rem;
+  font-weight: 600;
+  background: rgba(0, 0, 0, 0.15);
+  border-radius: 10px;
+}
+
+.tag-cloud-item:not(.has-color) .tag-count {
+  background: var(--background-tertiary);
+}
+
+/* Selection Info */
+.tag-selection-info {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  margin-top: 16px;
+  padding: 12px 16px;
+  background: var(--accent-color-transparent);
+  border-radius: 6px;
+  font-size: 0.9rem;
+}
+
+.tag-selection-info button {
+  font-size: 0.85rem;
+  padding: 4px 12px;
+}
+
+/* Forms */
+.tag-create-form,
+.tag-edit-form,
+.merge-form {
+  margin-bottom: 16px;
+}
+
+.tag-create-form h4,
+.tag-edit-form h4 {
+  margin: 0 0 12px 0;
+  font-size: 1rem;
+  font-weight: 500;
+  color: var(--text-primary);
+}
+
+.tag-form-row {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  flex-wrap: wrap;
+}
+
+.tag-form-row input[type="text"] {
+  flex: 1;
+  min-width: 200px;
+  padding: 8px 12px;
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  background: var(--background-primary);
+  color: var(--text-primary);
+  font-family: inherit;
+  font-size: 0.95rem;
+}
+
+.tag-form-row input[type="text"]:focus {
+  outline: none;
+  border-color: var(--accent-color);
+}
+
+.tag-form-row select {
+  flex: 1;
+  min-width: 200px;
+  padding: 8px 12px;
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  background: var(--background-primary);
+  color: var(--text-primary);
+  font-family: inherit;
+  font-size: 0.95rem;
+}
+
+.tag-form-row select:focus {
+  outline: none;
+  border-color: var(--accent-color);
+}
+
+/* Color picker group */
+.color-picker-group {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+}
+
+.color-picker-group input[type="color"] {
+  width: 36px;
+  height: 36px;
+  padding: 2px;
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  cursor: pointer;
+  background: var(--background-primary);
+}
+
+.color-picker-group input[type="color"]::-webkit-color-swatch-wrapper {
+  padding: 2px;
+}
+
+.color-picker-group input[type="color"]::-webkit-color-swatch {
+  border-radius: 2px;
+  border: none;
+}
+
+.clear-color {
+  padding: 4px 8px !important;
+  font-size: 0.75rem !important;
+  min-width: auto !important;
+  background: var(--background-tertiary) !important;
+  border: none !important;
+}
+
+.clear-color:hover {
+  background: var(--background-hover) !important;
+}
+
+/* Color presets */
+.color-presets {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 6px;
+  margin-top: 12px;
+}
+
+.color-preset {
+  width: 24px;
+  height: 24px;
+  border: 2px solid transparent;
+  border-radius: 4px;
+  cursor: pointer;
+  transition: transform 0.1s ease, border-color 0.1s ease;
+}
+
+.color-preset:hover {
+  transform: scale(1.15);
+  border-color: var(--text-secondary);
+}
+
+/* Tag preview */
+.tag-preview {
+  display: inline-flex;
+  align-items: center;
+  padding: 6px 12px;
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  font-size: 0.95rem;
+}
+
+/* Buttons */
+.tags-view button {
+  padding: 8px 16px;
+  border: 1px solid var(--border-color);
+  border-radius: 4px;
+  background: var(--background-primary);
+  color: var(--text-primary);
+  font-family: inherit;
+  font-size: 0.9rem;
+  cursor: pointer;
+  transition: all 0.15s ease;
+}
+
+.tags-view button:hover {
+  background: var(--background-hover);
+  border-color: var(--text-secondary);
+}
+
+.tags-view button:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
+.tags-view button.primary {
+  background: var(--accent-color);
+  border-color: var(--accent-color);
+  color: white;
+}
+
+.tags-view button.primary:hover {
+  opacity: 0.9;
+}
+
+.tags-view button.danger {
+  background: #ef4444;
+  border-color: #ef4444;
+  color: white;
+}
+
+.tags-view button.danger:hover {
+  opacity: 0.9;
+}
+
+/* Confirm Dialog */
+.confirm-dialog-overlay {
+  position: fixed;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background: rgba(0, 0, 0, 0.5);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 1000;
+}
+
+.confirm-dialog {
+  background: var(--background-primary);
+  border: 1px solid var(--border-color);
+  border-radius: 8px;
+  padding: 24px;
+  max-width: 450px;
+  width: 90%;
+  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.2);
+}
+
+.confirm-dialog h3 {
+  margin: 0 0 12px 0;
+  font-size: 1.2rem;
+  font-weight: 600;
+  color: var(--text-primary);
+}
+
+.confirm-dialog p {
+  margin: 0 0 20px 0;
+  color: var(--text-secondary);
+  line-height: 1.5;
+}
+
+.confirm-dialog-actions {
+  display: flex;
+  justify-content: flex-end;
+  gap: 10px;
+}

src/renderer/components/TagsView/TagsView.tsx

@@ -0,0 +1,615 @@
+import React, { useState, useEffect, useCallback } from 'react';
+import { useAppStore } from '../../store';
+import { showToast } from '../Toast';
+import './TagsView.css';
+
+// Types
+interface TagWithCount {
+  name: string;
+  color: string | null;
+  count: number;
+}
+
+interface TagData {
+  id: string;
+  projectId: string;
+  name: string;
+  color?: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
+// Export category IDs for sidebar navigation
+export type TagsCategory = 'cloud' | 'manage' | 'merge';
+
+// Scroll to a tags section by category ID
+export const scrollToTagsSection = (category: TagsCategory) => {
+  const element = document.getElementById(`tags-section-${category}`);
+  if (element) {
+    element.scrollIntoView({ behavior: 'smooth', block: 'start' });
+  }
+};
+
+// Get contrasting text color for background
+const getContrastColor = (hex: string): string => {
+  // Remove # if present
+  const color = hex.replace('#', '');
+  
+  // Parse hex to RGB
+  let r: number, g: number, b: number;
+  if (color.length === 3) {
+    r = parseInt(color[0] + color[0], 16);
+    g = parseInt(color[1] + color[1], 16);
+    b = parseInt(color[2] + color[2], 16);
+  } else {
+    r = parseInt(color.substring(0, 2), 16);
+    g = parseInt(color.substring(2, 4), 16);
+    b = parseInt(color.substring(4, 6), 16);
+  }
+  
+  // Calculate relative luminance
+  const luminance = (0.299 * r + 0.587 * g + 0.114 * b) / 255;
+  
+  return luminance > 0.5 ? '#000000' : '#ffffff';
+};
+
+// Color picker presets
+const COLOR_PRESETS = [
+  '#ef4444', '#f97316', '#f59e0b', '#eab308', '#84cc16',
+  '#22c55e', '#10b981', '#14b8a6', '#06b6d4', '#0ea5e9',
+  '#3b82f6', '#6366f1', '#8b5cf6', '#a855f7', '#d946ef',
+  '#ec4899', '#f43f5e',
+];
+
+// Tag Cloud Item
+const TagCloudItem: React.FC<{
+  tag: TagWithCount;
+  isSelected: boolean;
+  onSelect: (name: string) => void;
+  maxCount: number;
+}> = ({ tag, isSelected, onSelect, maxCount }) => {
+  // Calculate font size based on count (range: 0.8rem to 2rem)
+  const minSize = 0.85;
+  const maxSize = 1.8;
+  const ratio = maxCount > 1 ? (tag.count - 1) / (maxCount - 1) : 0;
+  const fontSize = minSize + (maxSize - minSize) * ratio;
+
+  const hasColor = !!tag.color;
+  const style: React.CSSProperties = hasColor
+    ? {
+        backgroundColor: tag.color!,
+        color: getContrastColor(tag.color!),
+        fontSize: `${fontSize}rem`,
+      }
+    : {
+        fontSize: `${fontSize}rem`,
+      };
+
+  return (
+    <button
+      className={`tag-cloud-item ${isSelected ? 'selected' : ''} ${hasColor ? 'has-color' : ''}`}
+      style={style}
+      onClick={() => onSelect(tag.name)}
+      title={`${tag.count} post${tag.count !== 1 ? 's' : ''}`}
+    >
+      {tag.name}
+      <span className="tag-count">{tag.count}</span>
+    </button>
+  );
+};
+
+// Confirm Dialog for destructive actions
+const ConfirmDialog: React.FC<{
+  isOpen: boolean;
+  title: string;
+  message: string;
+  confirmText: string;
+  cancelText?: string;
+  isDestructive?: boolean;
+  onConfirm: () => void;
+  onCancel: () => void;
+}> = ({ isOpen, title, message, confirmText, cancelText = 'Cancel', isDestructive, onConfirm, onCancel }) => {
+  if (!isOpen) return null;
+
+  return (
+    <div className="confirm-dialog-overlay">
+      <div className="confirm-dialog">
+        <h3>{title}</h3>
+        <p>{message}</p>
+        <div className="confirm-dialog-actions">
+          <button onClick={onCancel}>{cancelText}</button>
+          <button 
+            className={isDestructive ? 'danger' : 'primary'}
+            onClick={onConfirm}
+          >
+            {confirmText}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+};
+
+// Section Header
+const SectionHeader: React.FC<{
+  id?: string;
+  title: string;
+  description?: string;
+  children: React.ReactNode;
+}> = ({ id, title, description, children }) => (
+  <div className="tags-section" id={id}>
+    <div className="tags-section-header">
+      <h3>{title}</h3>
+      {description && <p className="tags-section-description">{description}</p>}
+    </div>
+    <div className="tags-section-content">
+      {children}
+    </div>
+  </div>
+);
+
+export const TagsView: React.FC = () => {
+  const { showErrorModal } = useAppStore();
+  
+  // State
+  const [tagsWithCounts, setTagsWithCounts] = useState<TagWithCount[]>([]);
+  const [allTags, setAllTags] = useState<TagData[]>([]);
+  const [selectedTags, setSelectedTags] = useState<string[]>([]);
+  const [isLoading, setIsLoading] = useState(true);
+  
+  // Create tag form
+  const [newTagName, setNewTagName] = useState('');
+  const [newTagColor, setNewTagColor] = useState('');
+  
+  // Edit tag state
+  const [editingTagId, setEditingTagId] = useState<string | null>(null);
+  const [editTagColor, setEditTagColor] = useState<string>('');
+  const [editTagName, setEditTagName] = useState('');
+  
+  // Merge tags state
+  const [mergeTargetName, setMergeTargetName] = useState('');
+  
+  // Confirm dialogs
+  const [deleteConfirm, setDeleteConfirm] = useState<{ tagId: string; tagName: string } | null>(null);
+  const [mergeConfirm, setMergeConfirm] = useState<{ sourceNames: string[]; targetName: string } | null>(null);
+
+  // Load tags
+  const loadTags = useCallback(async () => {
+    try {
+      setIsLoading(true);
+      const [tagsWithCountsResult, allTagsResult] = await Promise.all([
+        window.electronAPI?.tags.getWithCounts(),
+        window.electronAPI?.tags.getAll(),
+      ]);
+      
+      if (tagsWithCountsResult) {
+        setTagsWithCounts(tagsWithCountsResult as TagWithCount[]);
+      }
+      if (allTagsResult) {
+        setAllTags(allTagsResult as TagData[]);
+      }
+    } catch (error) {
+      console.error('Failed to load tags:', error);
+    } finally {
+      setIsLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    loadTags();
+  }, [loadTags]);
+
+  // Listen for tag events
+  useEffect(() => {
+    const unsubscribers: Array<() => void> = [];
+
+    unsubscribers.push(
+      window.electronAPI?.on('tag:created', () => loadTags()) || (() => {})
+    );
+    unsubscribers.push(
+      window.electronAPI?.on('tag:updated', () => loadTags()) || (() => {})
+    );
+    unsubscribers.push(
+      window.electronAPI?.on('tag:deleted', () => loadTags()) || (() => {})
+    );
+    unsubscribers.push(
+      window.electronAPI?.on('tag:renamed', () => loadTags()) || (() => {})
+    );
+    unsubscribers.push(
+      window.electronAPI?.on('tags:merged', () => loadTags()) || (() => {})
+    );
+
+    return () => {
+      unsubscribers.forEach(unsub => unsub());
+    };
+  }, [loadTags]);
+
+  // Handle tag selection
+  const handleTagSelect = (name: string) => {
+    setSelectedTags(prev => {
+      if (prev.includes(name)) {
+        return prev.filter(n => n !== name);
+      }
+      return [...prev, name];
+    });
+  };
+
+  // Create tag
+  const handleCreateTag = async () => {
+    if (!newTagName.trim()) {
+      showToast.error('Tag name is required');
+      return;
+    }
+
+    try {
+      await window.electronAPI?.tags.create({
+        name: newTagName.trim(),
+        color: newTagColor || undefined,
+      });
+      setNewTagName('');
+      setNewTagColor('');
+      showToast.success('Tag created');
+      loadTags();
+    } catch (error) {
+      const err = error as Error;
+      showToast.error(err.message);
+    }
+  };
+
+  // Delete tag (with confirmation)
+  const handleDeleteTag = async () => {
+    if (!deleteConfirm) return;
+
+    try {
+      const result = await window.electronAPI?.tags.delete(deleteConfirm.tagId);
+      if (result?.success) {
+        showToast.success(`Tag deleted. ${result.postsUpdated} post(s) updated.`);
+        setSelectedTags(prev => prev.filter(n => n !== deleteConfirm.tagName));
+        loadTags();
+      }
+    } catch (error) {
+      const err = error as Error;
+      showErrorModal({
+        title: 'Delete Failed',
+        message: err.message,
+      });
+    } finally {
+      setDeleteConfirm(null);
+    }
+  };
+
+  // Start editing tag
+  const handleStartEdit = (tag: TagData) => {
+    setEditingTagId(tag.id);
+    setEditTagColor(tag.color || '');
+    setEditTagName(tag.name);
+  };
+
+  // Save tag edit
+  const handleSaveEdit = async () => {
+    if (!editingTagId) return;
+
+    try {
+      // Update color
+      await window.electronAPI?.tags.update(editingTagId, {
+        color: editTagColor || null,
+      });
+
+      // If name changed, rename the tag
+      const originalTag = allTags.find(t => t.id === editingTagId);
+      if (originalTag && originalTag.name !== editTagName.trim().toLowerCase()) {
+        await window.electronAPI?.tags.rename(editingTagId, editTagName.trim());
+      }
+
+      showToast.success('Tag updated');
+      setEditingTagId(null);
+      loadTags();
+    } catch (error) {
+      const err = error as Error;
+      showToast.error(err.message);
+    }
+  };
+
+  // Merge tags (with confirmation)
+  const handleMergeTags = async () => {
+    if (!mergeConfirm) return;
+
+    try {
+      // Find target tag
+      const targetTag = allTags.find(t => t.name === mergeConfirm.targetName);
+      if (!targetTag) {
+        showToast.error('Target tag not found');
+        return;
+      }
+
+      // Find source tag IDs
+      const sourceTags = allTags.filter(t => 
+        mergeConfirm.sourceNames.includes(t.name) && t.id !== targetTag.id
+      );
+
+      if (sourceTags.length === 0) {
+        showToast.error('No source tags to merge');
+        return;
+      }
+
+      const result = await window.electronAPI?.tags.merge(
+        sourceTags.map(t => t.id),
+        targetTag.id
+      );
+
+      if (result?.success) {
+        showToast.success(
+          `Merged ${result.tagsDeleted} tag(s) into "${result.targetTag}". ${result.postsUpdated} post(s) updated.`
+        );
+        setSelectedTags([]);
+        setMergeTargetName('');
+        loadTags();
+      }
+    } catch (error) {
+      const err = error as Error;
+      showErrorModal({
+        title: 'Merge Failed',
+        message: err.message,
+      });
+    } finally {
+      setMergeConfirm(null);
+    }
+  };
+
+  // Sync tags from posts
+  const handleSyncFromPosts = async () => {
+    try {
+      const result = await window.electronAPI?.tags.syncFromPosts();
+      if (result) {
+        if (result.added.length > 0) {
+          showToast.success(`Discovered ${result.added.length} new tag(s)`);
+        } else {
+          showToast.info('All tags are already synced');
+        }
+        loadTags();
+      }
+    } catch (error) {
+      const err = error as Error;
+      showToast.error(err.message);
+    }
+  };
+
+  // Clear selection
+  const handleClearSelection = () => {
+    setSelectedTags([]);
+  };
+
+  // Get max count for sizing
+  const maxCount = Math.max(...tagsWithCounts.map(t => t.count), 1);
+
+  // Selected tag objects
+  const selectedTagObjects = allTags.filter(t => selectedTags.includes(t.name));
+
+  return (
+    <div className="tags-view">
+      <div className="tags-view-header">
+        <h2>Tag Management</h2>
+        <p className="text-muted">Manage your blog's tags, assign colors, and perform bulk operations.</p>
+      </div>
+
+      <div className="tags-view-content">
+        {/* Tag Cloud Section */}
+        <SectionHeader
+          id="tags-section-cloud"
+          title="Tag Cloud"
+          description="Click tags to select them for bulk operations. Hover to see post counts."
+        >
+          {isLoading ? (
+            <div className="tags-loading">Loading tags...</div>
+          ) : tagsWithCounts.length === 0 ? (
+            <div className="tags-empty">
+              <p>No tags found</p>
+              <button onClick={handleSyncFromPosts}>Discover tags from posts</button>
+            </div>
+          ) : (
+            <>
+              <div className="tag-cloud">
+                {tagsWithCounts.map(tag => (
+                  <TagCloudItem
+                    key={tag.name}
+                    tag={tag}
+                    isSelected={selectedTags.includes(tag.name)}
+                    onSelect={handleTagSelect}
+                    maxCount={maxCount}
+                  />
+                ))}
+              </div>
+              {selectedTags.length > 0 && (
+                <div className="tag-selection-info">
+                  <span>{selectedTags.length} tag(s) selected</span>
+                  <button onClick={handleClearSelection}>Clear selection</button>
+                </div>
+              )}
+            </>
+          )}
+        </SectionHeader>
+
+        {/* Tag Management Section */}
+        <SectionHeader
+          id="tags-section-manage"
+          title="Create & Edit Tags"
+          description="Create new tags or edit existing ones. Assign colors to make tags visually distinct."
+        >
+          {/* Create new tag */}
+          <div className="tag-create-form">
+            <h4>Create New Tag</h4>
+            <div className="tag-form-row">
+              <input
+                type="text"
+                placeholder="Tag name"
+                value={newTagName}
+                onChange={(e) => setNewTagName(e.target.value)}
+                onKeyDown={(e) => e.key === 'Enter' && handleCreateTag()}
+              />
+              <div className="color-picker-group">
+                <input
+                  type="color"
+                  value={newTagColor || '#808080'}
+                  onChange={(e) => setNewTagColor(e.target.value)}
+                  title="Choose color"
+                />
+                {newTagColor && (
+                  <button 
+                    className="clear-color" 
+                    onClick={() => setNewTagColor('')}
+                    title="Remove color"
+                  >
+                    ✕
+                  </button>
+                )}
+              </div>
+              <button onClick={handleCreateTag} className="primary">Create</button>
+            </div>
+            <div className="color-presets">
+              {COLOR_PRESETS.map(color => (
+                <button
+                  key={color}
+                  className="color-preset"
+                  style={{ backgroundColor: color }}
+                  onClick={() => setNewTagColor(color)}
+                  title={color}
+                />
+              ))}
+            </div>
+          </div>
+
+          {/* Selected tag editor */}
+          {selectedTagObjects.length === 1 && (
+            <div className="tag-edit-form">
+              <h4>Edit Tag: {selectedTagObjects[0].name}</h4>
+              {editingTagId === selectedTagObjects[0].id ? (
+                <div className="tag-form-row">
+                  <input
+                    type="text"
+                    value={editTagName}
+                    onChange={(e) => setEditTagName(e.target.value)}
+                    placeholder="Tag name"
+                  />
+                  <div className="color-picker-group">
+                    <input
+                      type="color"
+                      value={editTagColor || '#808080'}
+                      onChange={(e) => setEditTagColor(e.target.value)}
+                    />
+                    {editTagColor && (
+                      <button 
+                        className="clear-color" 
+                        onClick={() => setEditTagColor('')}
+                        title="Remove color"
+                      >
+                        ✕
+                      </button>
+                    )}
+                  </div>
+                  <button onClick={handleSaveEdit} className="primary">Save</button>
+                  <button onClick={() => setEditingTagId(null)}>Cancel</button>
+                </div>
+              ) : (
+                <div className="tag-form-row">
+                  <span className="tag-preview" style={
+                    selectedTagObjects[0].color 
+                      ? { backgroundColor: selectedTagObjects[0].color, color: getContrastColor(selectedTagObjects[0].color) }
+                      : {}
+                  }>
+                    {selectedTagObjects[0].name}
+                  </span>
+                  <button onClick={() => handleStartEdit(selectedTagObjects[0])}>
+                    Edit
+                  </button>
+                  <button 
+                    className="danger"
+                    onClick={() => setDeleteConfirm({ 
+                      tagId: selectedTagObjects[0].id, 
+                      tagName: selectedTagObjects[0].name 
+                    })}
+                  >
+                    Delete
+                  </button>
+                </div>
+              )}
+            </div>
+          )}
+        </SectionHeader>
+
+        {/* Merge Tags Section */}
+        <SectionHeader
+          id="tags-section-merge"
+          title="Merge Tags"
+          description="Select multiple tags above, then merge them into a single tag. All posts will be updated."
+        >
+          {selectedTags.length < 2 ? (
+            <p className="text-muted">Select 2 or more tags from the cloud above to merge them.</p>
+          ) : (
+            <div className="merge-form">
+              <p>Merge <strong>{selectedTags.length}</strong> tags into:</p>
+              <div className="tag-form-row">
+                <select
+                  value={mergeTargetName}
+                  onChange={(e) => setMergeTargetName(e.target.value)}
+                >
+                  <option value="">Select target tag...</option>
+                  {selectedTags.map(name => (
+                    <option key={name} value={name}>{name}</option>
+                  ))}
+                </select>
+                <button
+                  className="primary"
+                  disabled={!mergeTargetName}
+                  onClick={() => {
+                    if (mergeTargetName) {
+                      setMergeConfirm({
+                        sourceNames: selectedTags.filter(n => n !== mergeTargetName),
+                        targetName: mergeTargetName,
+                      });
+                    }
+                  }}
+                >
+                  Merge Tags
+                </button>
+              </div>
+              <p className="text-muted text-small">
+                Tags to be deleted: {selectedTags.filter(n => n !== mergeTargetName).join(', ') || '(none)'}
+              </p>
+            </div>
+          )}
+        </SectionHeader>
+
+        {/* Sync Section */}
+        <SectionHeader
+          id="tags-section-sync"
+          title="Sync Tags"
+          description="Discover tags that exist in posts but not in the tag database."
+        >
+          <button onClick={handleSyncFromPosts}>
+            Sync Tags from Posts
+          </button>
+        </SectionHeader>
+      </div>
+
+      {/* Confirm Dialogs */}
+      <ConfirmDialog
+        isOpen={!!deleteConfirm}
+        title="Delete Tag"
+        message={`Are you sure you want to delete the tag "${deleteConfirm?.tagName}"? This will remove it from all posts. This action runs as a background task.`}
+        confirmText="Delete Tag"
+        isDestructive
+        onConfirm={handleDeleteTag}
+        onCancel={() => setDeleteConfirm(null)}
+      />
+
+      <ConfirmDialog
+        isOpen={!!mergeConfirm}
+        title="Merge Tags"
+        message={`Are you sure you want to merge ${mergeConfirm?.sourceNames.length} tag(s) into "${mergeConfirm?.targetName}"? The source tags will be deleted and all posts will be updated. This runs as a background task.`}
+        confirmText="Merge Tags"
+        onConfirm={handleMergeTags}
+        onCancel={() => setMergeConfirm(null)}
+      />
+    </div>
+  );
+};

src/renderer/components/TagsView/index.ts

@@ -0,0 +1,2 @@
+export { TagsView, scrollToTagsSection } from './TagsView';
+export type { TagsCategory } from './TagsView';

src/renderer/components/index.ts

@@ -12,5 +12,6 @@ export { TaskPopup } from './TaskPopup';
 export { ResizablePanel } from './ResizablePanel';
 export { CredentialsPanel } from './CredentialsPanel';
 export { SettingsView } from './SettingsView';
+export { TagsView, scrollToTagsSection, type TagsCategory } from './TagsView';
 export { PostLinks } from './PostLinks';
 export { ErrorModal, type ErrorDetails } from './ErrorModal';

src/renderer/store/appStore.ts

@@ -5,7 +5,7 @@ import { persist } from 'zustand/middleware';
 const STORAGE_KEY = 'bds-app-state';
 
 // Tab types
-export type TabType = 'post' | 'media' | 'settings';
+export type TabType = 'post' | 'media' | 'settings' | 'tags';
 
 export interface Tab {
   type: TabType;
@@ -88,7 +88,7 @@ interface AppState {
   activeTabId: string | null;
   
   // UI State
-  activeView: 'posts' | 'media' | 'settings';
+  activeView: 'posts' | 'media' | 'settings' | 'tags';
   sidebarVisible: boolean;
   panelVisible: boolean;
   selectedPostId: string | null;
@@ -136,7 +136,7 @@ interface AppState {
   restoreTabState: (state: TabState) => void;
   
   // Actions
-  setActiveView: (view: 'posts' | 'media' | 'settings') => void;
+  setActiveView: (view: 'posts' | 'media' | 'settings' | 'tags') => void;
   toggleSidebar: () => void;
   togglePanel: () => void;
   setSelectedPost: (id: string | null) => void;

src/renderer/types/electron.d.ts

@@ -131,6 +131,45 @@ export interface CategoryCount {
   count: number;
 }
 
+export interface TagData {
+  id: string;
+  projectId: string;
+  name: string;
+  color?: string;
+  createdAt: string;
+  updatedAt: string;
+}
+
+export interface TagWithCount {
+  name: string;
+  color: string | null;
+  count: number;
+}
+
+export interface DeleteTagResult {
+  success: boolean;
+  postsUpdated: number;
+}
+
+export interface MergeTagsResult {
+  success: boolean;
+  postsUpdated: number;
+  tagsDeleted: number;
+  targetTag: string;
+}
+
+export interface RenameTagResult {
+  success: boolean;
+  postsUpdated: number;
+  oldName: string;
+  newName: string;
+}
+
+export interface SyncTagsResult {
+  discovered: number;
+  added: string[];
+}
+
 export interface ElectronAPI {
   projects: {
     create: (data: { name: string; description?: string; slug?: string }) => Promise<ProjectData>;
@@ -223,6 +262,19 @@ export interface ElectronAPI {
     setProjectMetadata: (metadata: { name: string; description?: string }) => Promise<ProjectMetadata | null>;
     updateProjectMetadata: (updates: { name?: string; description?: string }) => Promise<ProjectMetadata | null>;
   };
+  tags: {
+    getAll: () => Promise<TagData[]>;
+    getWithCounts: () => Promise<TagWithCount[]>;
+    get: (id: string) => Promise<TagData | null>;
+    getByName: (name: string) => Promise<TagData | null>;
+    create: (data: { name: string; color?: string }) => Promise<TagData>;
+    update: (id: string, data: { name?: string; color?: string | null }) => Promise<TagData | null>;
+    delete: (id: string) => Promise<DeleteTagResult>;
+    merge: (sourceTagIds: string[], targetTagId: string) => Promise<MergeTagsResult>;
+    rename: (id: string, newName: string) => Promise<RenameTagResult>;
+    getPostsWithTag: (tagId: string) => Promise<string[]>;
+    syncFromPosts: () => Promise<SyncTagsResult>;
+  };
   on: (channel: string, callback: (...args: unknown[]) => void) => () => void;
   once: (channel: string, callback: (...args: unknown[]) => void) => void;
 }

tests/engine/TagEngine.test.ts

@@ -0,0 +1,482 @@
+/**
+ * TagEngine Unit Tests
+ *
+ * Tests the REAL TagEngine class with mocked dependencies.
+ * Following TDD best practices: mock external dependencies, test real implementation.
+ */
+
+import { describe, it, expect, beforeEach, vi, afterEach } from 'vitest';
+import { TagEngine, TagData, TagWithCount, MergeTagsResult, DeleteTagResult } from '../../src/main/engine/TagEngine';
+import { resetMockCounters } from '../utils/factories';
+
+// Create mock data stores
+const mockTags = new Map<string, any>();
+const mockPosts = new Map<string, any>();
+let mockExecuteArgs: any[] = [];
+
+// Create chainable mock for Drizzle ORM
+function createSelectChain() {
+  return {
+    from: vi.fn().mockReturnThis(),
+    where: vi.fn().mockImplementation(function(this: any) {
+      return this;
+    }),
+    orderBy: vi.fn().mockReturnThis(),
+    limit: vi.fn().mockReturnThis(),
+    offset: vi.fn().mockReturnThis(),
+    all: vi.fn().mockImplementation(() => Promise.resolve(Array.from(mockTags.values()))),
+    get: vi.fn().mockImplementation(() => Promise.resolve(undefined)),
+  };
+}
+
+function createDrizzleMock() {
+  return {
+    select: vi.fn(() => createSelectChain()),
+    insert: vi.fn(() => ({
+      values: vi.fn((data: any) => {
+        if (data && data.id) {
+          mockTags.set(data.id, data);
+        }
+        return Promise.resolve();
+      }),
+    })),
+    update: vi.fn(() => ({
+      set: vi.fn(() => ({
+        where: vi.fn(() => Promise.resolve()),
+      })),
+    })),
+    delete: vi.fn(() => ({
+      where: vi.fn(() => Promise.resolve()),
+    })),
+  };
+}
+
+const mockLocalDb = createDrizzleMock();
+const mockLocalClient = {
+  execute: vi.fn(async (query: { sql: string; args: any[] }) => {
+    mockExecuteArgs.push(query);
+    return { rows: [] };
+  }),
+};
+
+// Mock the database module
+vi.mock('../../src/main/database', () => ({
+  getDatabase: vi.fn(() => ({
+    getLocal: vi.fn(() => mockLocalDb),
+    getLocalClient: vi.fn(() => mockLocalClient),
+    getRemote: vi.fn(() => null),
+    getDataPaths: vi.fn(() => ({
+      database: '/mock/userData/bds.db',
+      posts: '/mock/userData/posts',
+      media: '/mock/userData/media',
+    })),
+    initializeLocal: vi.fn(),
+    initializeRemote: vi.fn(),
+    close: vi.fn(),
+  })),
+}));
+
+// Mock fs/promises
+vi.mock('fs/promises', () => ({
+  readFile: vi.fn(async () => '[]'),
+  writeFile: vi.fn(async () => {}),
+  unlink: vi.fn(async () => {}),
+  mkdir: vi.fn(async () => {}),
+  readdir: vi.fn(async () => []),
+  stat: vi.fn(async () => ({
+    isFile: () => false,
+    isDirectory: () => true,
+  })),
+  access: vi.fn(async () => {}),
+}));
+
+// Mock electron app
+vi.mock('electron', () => ({
+  app: {
+    getPath: vi.fn(() => '/mock/userData'),
+  },
+}));
+
+// Mock TaskManager
+vi.mock('../../src/main/engine/TaskManager', () => ({
+  taskManager: {
+    runTask: vi.fn(async (task: any) => {
+      // Execute the task for testing
+      return task.execute((progress: number, message: string) => {});
+    }),
+  },
+}));
+
+describe('TagEngine', () => {
+  let tagEngine: TagEngine;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockTags.clear();
+    mockPosts.clear();
+    mockExecuteArgs = [];
+    resetMockCounters();
+    tagEngine = new TagEngine();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  describe('constructor', () => {
+    it('should create a new TagEngine instance', () => {
+      expect(tagEngine).toBeDefined();
+      expect(tagEngine).toBeInstanceOf(TagEngine);
+    });
+  });
+
+  describe('setProjectContext', () => {
+    it('should set the current project ID', () => {
+      tagEngine.setProjectContext('project-123');
+      expect(tagEngine.getProjectContext()).toBe('project-123');
+    });
+  });
+
+  describe('getTagsWithCounts', () => {
+    it('should return an empty array when no tags exist', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({ rows: [] });
+      
+      const result = await tagEngine.getTagsWithCounts();
+      
+      expect(result).toEqual([]);
+    });
+
+    it('should return tags with their post counts', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [
+          { name: 'javascript', color: null, post_count: 5 },
+          { name: 'typescript', color: '#3178c6', post_count: 3 },
+        ],
+      });
+
+      const result = await tagEngine.getTagsWithCounts();
+
+      expect(result).toHaveLength(2);
+      expect(result[0]).toEqual({ name: 'javascript', color: null, count: 5 });
+      expect(result[1]).toEqual({ name: 'typescript', color: '#3178c6', count: 3 });
+    });
+  });
+
+  describe('createTag', () => {
+    it('should create a new tag with a name', async () => {
+      const result = await tagEngine.createTag({ name: 'react' });
+
+      expect(result).toBeDefined();
+      expect(result.name).toBe('react');
+      expect(result.id).toBeDefined();
+    });
+
+    it('should normalize tag name to lowercase', async () => {
+      const result = await tagEngine.createTag({ name: 'React' });
+
+      expect(result.name).toBe('react');
+    });
+
+    it('should create a new tag with a color', async () => {
+      const result = await tagEngine.createTag({ name: 'react', color: '#61dafb' });
+
+      expect(result.name).toBe('react');
+      expect(result.color).toBe('#61dafb');
+    });
+
+    it('should emit tagCreated event', async () => {
+      const handler = vi.fn();
+      tagEngine.on('tagCreated', handler);
+
+      await tagEngine.createTag({ name: 'vue' });
+
+      expect(handler).toHaveBeenCalledWith(expect.objectContaining({ name: 'vue' }));
+    });
+
+    it('should throw error for empty tag name', async () => {
+      await expect(tagEngine.createTag({ name: '' })).rejects.toThrow('Tag name is required');
+    });
+
+    it('should throw error for duplicate tag name', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ id: 'existing', name: 'react' }],
+      });
+
+      await expect(tagEngine.createTag({ name: 'react' })).rejects.toThrow('Tag "react" already exists');
+    });
+  });
+
+  describe('updateTag', () => {
+    it('should update tag color', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ id: 'tag-1', name: 'react', color: null }],
+      });
+
+      const result = await tagEngine.updateTag('tag-1', { color: '#61dafb' });
+
+      expect(result).toBeDefined();
+      expect(result?.color).toBe('#61dafb');
+    });
+
+    it('should emit tagUpdated event', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ id: 'tag-1', name: 'react', color: null }],
+      });
+      
+      const handler = vi.fn();
+      tagEngine.on('tagUpdated', handler);
+
+      await tagEngine.updateTag('tag-1', { color: '#61dafb' });
+
+      expect(handler).toHaveBeenCalled();
+    });
+
+    it('should return null for non-existent tag', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({ rows: [] });
+
+      const result = await tagEngine.updateTag('non-existent', { color: '#fff' });
+
+      expect(result).toBeNull();
+    });
+  });
+
+  describe('deleteTag', () => {
+    it('should delete tag and remove from posts as a background task', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'react', color: null }] }) // Find tag
+        .mockResolvedValueOnce({ rows: [
+          { id: 'post-1', tags: '["react", "typescript"]' },
+          { id: 'post-2', tags: '["react"]' },
+        ] }) // Posts with tag
+        .mockResolvedValueOnce({ rows: [] }) // Update post-1
+        .mockResolvedValueOnce({ rows: [] }) // Update post-2
+        .mockResolvedValueOnce({ rows: [] }); // Delete tag
+
+      const result = await tagEngine.deleteTag('tag-1');
+
+      expect(result.success).toBe(true);
+      expect(result.postsUpdated).toBe(2);
+    });
+
+    it('should emit tagDeleted event', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'react', color: null }] })
+        .mockResolvedValueOnce({ rows: [] })
+        .mockResolvedValueOnce({ rows: [] });
+
+      const handler = vi.fn();
+      tagEngine.on('tagDeleted', handler);
+
+      await tagEngine.deleteTag('tag-1');
+
+      expect(handler).toHaveBeenCalledWith('tag-1');
+    });
+
+    it('should throw error for non-existent tag', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({ rows: [] });
+
+      await expect(tagEngine.deleteTag('non-existent')).rejects.toThrow('Tag not found');
+    });
+  });
+
+  describe('mergeTags', () => {
+    it('should merge multiple tags into one', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'js' }] }) // Source tag 1
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-2', name: 'javascript' }] }) // Source tag 2
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-3', name: 'ecmascript' }] }) // Target tag
+        .mockResolvedValueOnce({ rows: [{ id: 'post-1' }, { id: 'post-2' }] }) // Posts with source tags
+        .mockResolvedValueOnce({ rows: [] }) // Update posts
+        .mockResolvedValueOnce({ rows: [] }) // Delete source tag 1
+        .mockResolvedValueOnce({ rows: [] }); // Delete source tag 2
+
+      const result = await tagEngine.mergeTags(['tag-1', 'tag-2'], 'tag-3');
+
+      expect(result.success).toBe(true);
+      expect(result.postsUpdated).toBeGreaterThanOrEqual(0);
+      expect(result.tagsDeleted).toBe(2);
+    });
+
+    it('should emit tagsMerged event', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'js' }] })
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-2', name: 'javascript' }] })
+        .mockResolvedValueOnce({ rows: [] })
+        .mockResolvedValueOnce({ rows: [] });
+
+      const handler = vi.fn();
+      tagEngine.on('tagsMerged', handler);
+
+      await tagEngine.mergeTags(['tag-1'], 'tag-2');
+
+      expect(handler).toHaveBeenCalled();
+    });
+
+    it('should throw error when source tags array is empty', async () => {
+      await expect(tagEngine.mergeTags([], 'tag-1')).rejects.toThrow('Source tags are required');
+    });
+
+    it('should throw error when target tag does not exist', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'js' }] })
+        .mockResolvedValueOnce({ rows: [] }); // Target not found
+
+      await expect(tagEngine.mergeTags(['tag-1'], 'non-existent')).rejects.toThrow('Target tag not found');
+    });
+  });
+
+  describe('renameTags (batch rename)', () => {
+    it('should rename multiple tags and update posts', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'old-name' }] })
+        .mockResolvedValueOnce({ rows: [] }) // Check no duplicate
+        .mockResolvedValueOnce({ rows: [{ id: 'post-1' }] }) // Posts with tag
+        .mockResolvedValueOnce({ rows: [] }) // Update posts
+        .mockResolvedValueOnce({ rows: [] }); // Update tag name
+
+      const result = await tagEngine.renameTag('tag-1', 'new-name');
+
+      expect(result.success).toBe(true);
+      expect(result.postsUpdated).toBeGreaterThanOrEqual(0);
+    });
+
+    it('should emit tagRenamed event', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ id: 'tag-1', name: 'old-name' }] })
+        .mockResolvedValueOnce({ rows: [] })
+        .mockResolvedValueOnce({ rows: [] })
+        .mockResolvedValueOnce({ rows: [] });
+
+      const handler = vi.fn();
+      tagEngine.on('tagRenamed', handler);
+
+      await tagEngine.renameTag('tag-1', 'new-name');
+
+      expect(handler).toHaveBeenCalledWith(expect.objectContaining({
+        oldName: 'old-name',
+        newName: 'new-name',
+      }));
+    });
+  });
+
+  describe('getTag', () => {
+    it('should return tag by ID', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ id: 'tag-1', name: 'react', color: '#61dafb', project_id: 'default', created_at: Date.now(), updated_at: Date.now() }],
+      });
+
+      const result = await tagEngine.getTag('tag-1');
+
+      expect(result).toBeDefined();
+      expect(result?.name).toBe('react');
+      expect(result?.color).toBe('#61dafb');
+    });
+
+    it('should return null for non-existent tag', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({ rows: [] });
+
+      const result = await tagEngine.getTag('non-existent');
+
+      expect(result).toBeNull();
+    });
+  });
+
+  describe('getTagByName', () => {
+    it('should return tag by name', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ id: 'tag-1', name: 'react', color: '#61dafb', project_id: 'default', created_at: Date.now(), updated_at: Date.now() }],
+      });
+
+      const result = await tagEngine.getTagByName('react');
+
+      expect(result).toBeDefined();
+      expect(result?.id).toBe('tag-1');
+    });
+
+    it('should be case-insensitive', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ id: 'tag-1', name: 'react', color: null }],
+      });
+
+      const result = await tagEngine.getTagByName('REACT');
+
+      expect(result).toBeDefined();
+    });
+  });
+
+  describe('getAllTags', () => {
+    it('should return all tags for the current project', async () => {
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [
+          { id: 'tag-1', name: 'react', color: null, project_id: 'default', created_at: Date.now(), updated_at: Date.now() },
+          { id: 'tag-2', name: 'vue', color: '#42b883', project_id: 'default', created_at: Date.now(), updated_at: Date.now() },
+        ],
+      });
+
+      const result = await tagEngine.getAllTags();
+
+      expect(result).toHaveLength(2);
+      expect(result.map(t => t.name)).toContain('react');
+      expect(result.map(t => t.name)).toContain('vue');
+    });
+  });
+
+  describe('getPostsWithTag', () => {
+    it('should return post IDs that have the specified tag', async () => {
+      // First call: get tag name from id
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [{ name: 'react' }],
+      });
+      // Second call: find posts with this tag
+      mockLocalClient.execute.mockResolvedValueOnce({
+        rows: [
+          { id: 'post-1', tags: '["react", "typescript"]' },
+          { id: 'post-2', tags: '["react"]' },
+        ],
+      });
+
+      const result = await tagEngine.getPostsWithTag('tag-1');
+
+      expect(result).toHaveLength(2);
+      expect(result).toContain('post-1');
+      expect(result).toContain('post-2');
+    });
+  });
+
+  describe('color validation', () => {
+    it('should accept valid hex color codes', async () => {
+      const result = await tagEngine.createTag({ name: 'test', color: '#ff0000' });
+      expect(result.color).toBe('#ff0000');
+    });
+
+    it('should accept short hex color codes', async () => {
+      const result = await tagEngine.createTag({ name: 'test', color: '#f00' });
+      expect(result.color).toBe('#f00');
+    });
+
+    it('should reject invalid color codes', async () => {
+      await expect(tagEngine.createTag({ name: 'test', color: 'red' }))
+        .rejects.toThrow('Invalid color format');
+    });
+
+    it('should allow null/undefined color', async () => {
+      const result = await tagEngine.createTag({ name: 'test' });
+      expect(result.color).toBeUndefined();
+    });
+  });
+
+  describe('syncTagsFromPosts', () => {
+    it('should discover tags from existing posts and add missing ones', async () => {
+      mockLocalClient.execute
+        .mockResolvedValueOnce({ rows: [{ tags: '["react", "javascript"]' }, { tags: '["vue", "typescript"]' }] }) // Get posts
+        .mockResolvedValueOnce({ rows: [{ name: 'react' }] }) // Existing tags
+        .mockResolvedValueOnce({ rows: [] }) // Insert missing tags
+        .mockResolvedValueOnce({ rows: [] })
+        .mockResolvedValueOnce({ rows: [] });
+
+      const result = await tagEngine.syncTagsFromPosts();
+
+      expect(result.discovered).toBeGreaterThanOrEqual(0);
+    });
+  });
+});