diff --git a/src/main/ai/AiWorker.ts b/src/main/ai/AiWorker.ts
index 76718dc..ecf47c3 100644
--- a/src/main/ai/AiWorker.ts
+++ b/src/main/ai/AiWorker.ts
@@ -186,9 +186,9 @@ export class AiWorker {
           }).catch(() => {});
           // v0.2.3 #3 — per-tag vocab hit/miss 분류 (updateAiResult 후 → tagId 보장)
           // dedup: AI 응답에 같은 태그 중복 가능 — INSERT OR IGNORE 와 정합한 1-emit/태그 보장
-          const vocabSet = new Set(vocab);
+          const vocabSet = new Set(vocab.map((v) => v.toLowerCase()));
           for (const tagName of new Set(res.tags)) {
-            if (vocabSet.has(tagName)) {
+            if (vocabSet.has(tagName.toLowerCase())) {
               const tagId = this.repo.getTagIdByName(tagName);
               if (tagId !== null) {
                 await this.telemetry.emit({
diff --git a/tests/unit/AiWorker.test.ts b/tests/unit/AiWorker.test.ts
index 7b63311..93ec987 100644
--- a/tests/unit/AiWorker.test.ts
+++ b/tests/unit/AiWorker.test.ts
@@ -560,3 +560,91 @@ describe('AiWorker — vocab fetch + per-tag hit/miss (v0.2.3 #3 T7)', () => {
     expect(miss).toHaveLength(1);  // 'meeting' 1 miss
   });
 });
+
+describe('vocab COLLATE NOCASE', () => {
+  let db: Database.Database;
+  let repo: NoteRepository;
+
+  beforeEach(() => {
+    db = new Database(':memory:');
+    runMigrations(db);
+    repo = new NoteRepository(db);
+  });
+
+  it('hits when vocab has lowercase and AI returns capital', async () => {
+    // Pre-seed: 'design' in vocab (lowercase)
+    const seed = repo.create({ rawText: 'seed' }).id;
+    repo.updateAiResult(seed, { title: 't', summary: 'a\nb\nc', tags: ['design'], provider: 'p' });
+
+    const { id } = repo.create({ rawText: 'x' });
+    const provider = makeProvider({
+      generate: vi.fn(async () => ({
+        title: 't', summary: 'a\nb\nc',
+        tags: ['Design'],  // AI returns capitalized — DB COLLATE NOCASE matches 'design'
+        dueDate: null
+      }))
+    });
+    const emits: EmittedEvent[] = [];
+    const w = new AiWorker(repo, new ProviderHolder(provider), {
+      backoffsMs: [0, 0, 0],
+      telemetry: { emit: vi.fn(async (input) => { emits.push(input); }) }
+    });
+    await w.enqueue(id);
+    await w.drain();
+    expect(emits.filter((e) => e.kind === 'tag_vocab_hit')).toHaveLength(1);
+    expect(emits.filter((e) => e.kind === 'tag_vocab_miss')).toHaveLength(0);
+  });
+
+  it('hits when vocab has capital and AI returns lowercase', async () => {
+    // Scenario: vocab contains 'Design' (capital), AI returns 'design' (lowercase).
+    // getTopUsedTags filters via KEBAB_CASE_RE (/^[a-z0-9-]+$/) so 'Design' would be
+    // stripped in production. We stub getTopUsedTags to inject the capital vocab directly,
+    // and pre-seed the DB so getTagIdByName (COLLATE NOCASE) can resolve 'design' → tagId.
+    const seed = repo.create({ rawText: 'seed' }).id;
+    repo.updateAiResult(seed, { title: 't', summary: 'a\nb\nc', tags: ['Design'], provider: 'p' });
+    // Inject capital vocab bypassing the kebab filter
+    vi.spyOn(repo, 'getTopUsedTags').mockReturnValueOnce(['Design']);
+
+    const { id } = repo.create({ rawText: 'x' });
+    const provider = makeProvider({
+      generate: vi.fn(async () => ({
+        title: 't', summary: 'a\nb\nc',
+        tags: ['design'],  // AI returns lowercase — DB COLLATE NOCASE matches 'Design'
+        dueDate: null
+      }))
+    });
+    const emits: EmittedEvent[] = [];
+    const w = new AiWorker(repo, new ProviderHolder(provider), {
+      backoffsMs: [0, 0, 0],
+      telemetry: { emit: vi.fn(async (input) => { emits.push(input); }) }
+    });
+    await w.enqueue(id);
+    await w.drain();
+    expect(emits.filter((e) => e.kind === 'tag_vocab_hit')).toHaveLength(1);
+    expect(emits.filter((e) => e.kind === 'tag_vocab_miss')).toHaveLength(0);
+  });
+
+  it('still hits when both vocab and AI tag are same lowercase (regression)', async () => {
+    // Pre-seed: 'design' in vocab (lowercase)
+    const seed = repo.create({ rawText: 'seed' }).id;
+    repo.updateAiResult(seed, { title: 't', summary: 'a\nb\nc', tags: ['design'], provider: 'p' });
+
+    const { id } = repo.create({ rawText: 'x' });
+    const provider = makeProvider({
+      generate: vi.fn(async () => ({
+        title: 't', summary: 'a\nb\nc',
+        tags: ['design'],  // same lowercase — should still hit
+        dueDate: null
+      }))
+    });
+    const emits: EmittedEvent[] = [];
+    const w = new AiWorker(repo, new ProviderHolder(provider), {
+      backoffsMs: [0, 0, 0],
+      telemetry: { emit: vi.fn(async (input) => { emits.push(input); }) }
+    });
+    await w.enqueue(id);
+    await w.drain();
+    expect(emits.filter((e) => e.kind === 'tag_vocab_hit')).toHaveLength(1);
+    expect(emits.filter((e) => e.kind === 'tag_vocab_miss')).toHaveLength(0);
+  });
+});