diff --git a/src/main/repository/NoteRepository.ts b/src/main/repository/NoteRepository.ts
index e50bc2d..782bc86 100644
--- a/src/main/repository/NoteRepository.ts
+++ b/src/main/repository/NoteRepository.ts
@@ -11,6 +11,10 @@ export interface CreateNoteInput {
    * 미지정 시 기존 'pending' default + pending_jobs enqueue (backward compat).
    */
   aiStatus?: AiStatus;
+  /**
+   * v0.4 — 미지정 시 가장 오래된 notebook (default notebook) 의 id 자동 사용.
+   */
+  notebookId?: string;
 }
 
 export interface NewMediaRow {
@@ -83,11 +87,12 @@ export class NoteRepository {
     const id = uuidv7();
     const ts = now.toISOString();
     const aiStatus: AiStatus = input.aiStatus ?? 'pending';
+    const notebookId = input.notebookId ?? this.getDefaultNotebookId();
     const tx = this.db.transaction(() => {
       this.db
-        .prepare(`INSERT INTO notes (id, raw_text, ai_status, created_at, updated_at)
-                  VALUES (?, ?, ?, ?, ?)`)
-        .run(id, input.rawText, aiStatus, ts, ts);
+        .prepare(`INSERT INTO notes (id, raw_text, ai_status, created_at, updated_at, notebook_id)
+                  VALUES (?, ?, ?, ?, ?, ?)`)
+        .run(id, input.rawText, aiStatus, ts, ts, notebookId);
       this.db
         .prepare(`INSERT INTO note_revisions (note_id, raw_text, edited_at, edited_by)
                   VALUES (?, ?, ?, 'capture')`)
@@ -104,6 +109,16 @@ export class NoteRepository {
     return { id };
   }
 
+  private getDefaultNotebookId(): string {
+    const r = this.db
+      .prepare(`SELECT id FROM notebooks ORDER BY created_at ASC LIMIT 1`)
+      .get() as { id: string } | undefined;
+    if (!r) {
+      throw new Error('No default notebook found — m008 migration may not have run');
+    }
+    return r.id;
+  }
+
   insertMedia(rows: NewMediaRow[]): void {
     if (rows.length === 0) return;
     const now = new Date().toISOString();
@@ -897,14 +912,15 @@ export class NoteRepository {
       finalId = uuidv7();
       status = 'forked';
     }
+    const notebookId = this.getDefaultNotebookId();
     const tx = this.db.transaction(() => {
       this.db
         .prepare(
           `INSERT INTO notes
              (id, raw_text, ai_title, ai_summary, ai_status, ai_provider, ai_generated_at,
               title_edited_by_user, summary_edited_by_user,
-              user_intent, intent_prompted_at, deleted_at, created_at, updated_at)
-           VALUES (?, ?, ?, ?, 'done', ?, ?, ?, ?, ?, ?, ?, ?, ?)`
+              user_intent, intent_prompted_at, deleted_at, created_at, updated_at, notebook_id)
+           VALUES (?, ?, ?, ?, 'done', ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
         )
         .run(
           finalId,
@@ -919,7 +935,8 @@ export class NoteRepository {
           input.intentPromptedAt,
           input.deletedAt ?? null,
           input.createdAt,
-          input.updatedAt
+          input.updatedAt,
+          notebookId
         );
       this.db
         .prepare(
@@ -970,6 +987,7 @@ export class NoteRepository {
 
     if (!existing) {
       // INSERT path
+      const notebookId = this.getDefaultNotebookId();
       const tx = this.db.transaction(() => {
         this.db
           .prepare(
@@ -979,8 +997,8 @@ export class NoteRepository {
                 user_intent, intent_prompted_at,
                 created_at, updated_at,
                 due_date, due_date_edited_by_user,
-                status, status_changed_at, move_reason)
-             VALUES (?, ?, ?, ?, 'done', ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
+                status, status_changed_at, move_reason, notebook_id)
+             VALUES (?, ?, ?, ?, 'done', ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
           )
           .run(
             input.id,
@@ -999,7 +1017,8 @@ export class NoteRepository {
             input.dueDateEditedByUser ? 1 : 0,
             input.status,
             input.statusChangedAt,
-            input.moveReason
+            input.moveReason,
+            notebookId
           );
         this.db
           .prepare(
@@ -1223,7 +1242,8 @@ export class NoteRepository {
       createdAt: row.created_at as string,
       updatedAt: row.updated_at as string,
       tags: tags as NoteTag[],
-      media
+      media,
+      notebookId: row.notebook_id as string
     };
   }
 }
diff --git a/src/shared/types.ts b/src/shared/types.ts
index 1ad2a02..7a09150 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -92,6 +92,8 @@ export interface Note {
   updatedAt: string;
   tags: NoteTag[];
   media: NoteMedia[];
+  // v0.4 — m008 마이그레이션 보장 (notebook_id NOT NULL, default notebook 자동 할당).
+  notebookId: string;
 }
 
 // v0.4 — Notebook: 노트 묶음 단위. noteCount = status='active' 노트 수.
diff --git a/tests/unit/NoteCard.test.tsx b/tests/unit/NoteCard.test.tsx
index 106877c..f8d8f15 100644
--- a/tests/unit/NoteCard.test.tsx
+++ b/tests/unit/NoteCard.test.tsx
@@ -69,7 +69,8 @@ const baseNote: Note = {
   media: [
     { id: 'm1', kind: 'image', relPath: 'media/n1/img1.png', mime: 'image/png', bytes: 100 },
     { id: 'm2', kind: 'image', relPath: 'media/n1/img2.jpg', mime: 'image/jpeg', bytes: 200 }
-  ]
+  ],
+  notebookId: 'nb-default'
 };
 
 describe('NoteCard — image rendering', () => {
diff --git a/tests/unit/NoteRepository.test.ts b/tests/unit/NoteRepository.test.ts
index 05ad736..f5289a6 100644
--- a/tests/unit/NoteRepository.test.ts
+++ b/tests/unit/NoteRepository.test.ts
@@ -1222,3 +1222,36 @@ describe('NoteRepository — notes_fts tags sync (v0.2.11 Cut D)', () => {
     expect(row.tags).toBe('결재');
   });
 });
+
+describe('NoteRepository.create with notebook', () => {
+  let db: Database.Database;
+  let repo: NoteRepository;
+  let defaultId: string;
+
+  beforeEach(() => {
+    db = new Database(':memory:');
+    db.pragma('foreign_keys = ON');
+    runMigrations(db);
+    repo = new NoteRepository(db);
+    defaultId = (db.prepare(`SELECT id FROM notebooks`).get() as { id: string }).id;
+  });
+
+  it('notebook_id 미지정 시 default notebook 으로 들어감', () => {
+    const { id } = repo.create({ rawText: 'hello' });
+    const r = repo.findById(id);
+    expect(r?.notebookId).toBe(defaultId);
+  });
+
+  it('notebook_id 지정 시 그 값 보존', () => {
+    db.prepare(`INSERT INTO notebooks(id,name,created_at,updated_at) VALUES('nb-other','회사','2026-05-14','2026-05-14')`).run();
+    const { id } = repo.create({ rawText: 'hi', notebookId: 'nb-other' });
+    expect(repo.findById(id)?.notebookId).toBe('nb-other');
+  });
+
+  it('hydrate 가 notebookId 필드 반환', () => {
+    const { id } = repo.create({ rawText: 'hi' });
+    const r = repo.findById(id);
+    expect(typeof r?.notebookId).toBe('string');
+    expect(r?.notebookId).toBe(defaultId);
+  });
+});
diff --git a/tests/unit/store.expired.test.ts b/tests/unit/store.expired.test.ts
index 7f2406d..d6169e6 100644
--- a/tests/unit/store.expired.test.ts
+++ b/tests/unit/store.expired.test.ts
@@ -34,7 +34,7 @@ const noteStub = (id: string): Note => ({
   deletedAt: null, lastRecalledAt: null, recallDismissedAt: null,
   status: 'active', statusChangedAt: null, moveReason: null,
   createdAt: '2026-05-01T00:00:00Z', updatedAt: '2026-05-01T00:00:00Z',
-  tags: [], media: []
+  tags: [], media: [], notebookId: 'nb-default'
 });
 
 describe('useInbox — expired state (v0.2.3 #5)', () => {
diff --git a/tests/unit/store.recall.test.ts b/tests/unit/store.recall.test.ts
index 43e636a..8102358 100644
--- a/tests/unit/store.recall.test.ts
+++ b/tests/unit/store.recall.test.ts
@@ -38,7 +38,8 @@ const note = (id: string): Note => ({
   userIntent: null, intentPromptedAt: null,
   createdAt: new Date().toISOString(), updatedAt: new Date().toISOString(),
   deletedAt: null, lastRecalledAt: null, recallDismissedAt: null,
-  status: 'active', statusChangedAt: null, moveReason: null
+  status: 'active', statusChangedAt: null, moveReason: null,
+  notebookId: 'nb-default'
 });
 
 describe('store recall actions', () => {
diff --git a/tests/unit/store.tagFilter.test.ts b/tests/unit/store.tagFilter.test.ts
index 19d1329..4d5350f 100644
--- a/tests/unit/store.tagFilter.test.ts
+++ b/tests/unit/store.tagFilter.test.ts
@@ -27,7 +27,8 @@ function sample(id: string, tags: string[]): Note {
     createdAt: '2026-04-26T00:00:00Z',
     updatedAt: '2026-04-26T00:00:00Z',
     tags: tags.map((name) => ({ name, source: 'ai' as const })),
-    media: []
+    media: [],
+    notebookId: 'nb-default'
   };
 }
 
diff --git a/tests/unit/store.trash.test.ts b/tests/unit/store.trash.test.ts
index e124365..e52b7dd 100644
--- a/tests/unit/store.trash.test.ts
+++ b/tests/unit/store.trash.test.ts
@@ -32,7 +32,7 @@ const noteStub = (id: string, deletedAt: string | null = null): Note => ({
   deletedAt, lastRecalledAt: null, recallDismissedAt: null,
   status: deletedAt ? 'trashed' : 'active', statusChangedAt: deletedAt, moveReason: null,
   createdAt: '2026-05-01T00:00:00Z', updatedAt: '2026-05-01T00:00:00Z',
-  tags: [], media: []
+  tags: [], media: [], notebookId: 'nb-default'
 });
 
 describe('useInbox — trash state (v0.2.3 #4)', () => {