diff --git a/src/main/infra/db.test.ts b/src/main/infra/db.test.ts
index 6577918..544a8c1 100644
--- a/src/main/infra/db.test.ts
+++ b/src/main/infra/db.test.ts
@@ -72,6 +72,24 @@ describe('openDatabase', () => {
         expect(c?.c).toBe(2);
     });
 
+    test('chunk_index table accepts insert + UNIQUE(item_id, chunk_seq)', () => {
+        db = openDatabase(path.join(tmpDir, 'chunk.db'));
+        db.run(
+            'INSERT INTO chunk_index(item_id, chunk_seq, sha1_hex, bytes) VALUES (?, ?, ?, ?)',
+            ['item1', 0, 'abc123', 1024]
+        );
+        const handle = db;
+        expect(() => {
+            handle.run(
+                'INSERT INTO chunk_index(item_id, chunk_seq, sha1_hex, bytes) VALUES (?, ?, ?, ?)',
+                ['item1', 0, 'different', 2048]
+            );
+        }).toThrow(); // UNIQUE violation
+        const rows = handle.all<{ sha1_hex: string }>('SELECT sha1_hex FROM chunk_index WHERE item_id = ?', ['item1']);
+        expect(rows).toHaveLength(1);
+        expect(rows[0].sha1_hex).toBe('abc123');
+    });
+
     test('oauth_accounts table exists and accepts insert', () => {
         db = openDatabase(path.join(tmpDir, 'oauth.db'));
         db.run(
diff --git a/src/main/infra/schema-v5.ts b/src/main/infra/schema-v5.ts
index 0df1612..72c1a61 100644
--- a/src/main/infra/schema-v5.ts
+++ b/src/main/infra/schema-v5.ts
@@ -64,6 +64,19 @@ CREATE TABLE IF NOT EXISTS archive_files (
 
 CREATE INDEX IF NOT EXISTS idx_archive_streamer ON archive_files(streamer_login);
 
+CREATE TABLE IF NOT EXISTS chunk_index (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    item_id TEXT NOT NULL,
+    chunk_seq INTEGER NOT NULL,
+    sha1_hex TEXT NOT NULL,
+    bytes INTEGER NOT NULL,
+    created_at INTEGER NOT NULL DEFAULT (strftime('%s','now')),
+    UNIQUE(item_id, chunk_seq)
+);
+
+CREATE INDEX IF NOT EXISTS idx_chunk_item ON chunk_index(item_id);
+CREATE INDEX IF NOT EXISTS idx_chunk_sha1 ON chunk_index(sha1_hex);
+
 CREATE TABLE IF NOT EXISTS oauth_accounts (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
     provider TEXT NOT NULL,