Add regression test for book duration with disabled tracks

Demonstrates #5311: disabling an audio track via updateTracks does not
recompute the stored book duration, so it keeps counting the excluded
track. This test fails until the fix is applied (expects duration to
drop to only the enabled track's length).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/server/controllers/LibraryItemController.test.js

@@ -8,6 +8,7 @@ const LibraryItemController = require('../../../server/controllers/LibraryItemCo
 const ApiCacheManager = require('../../../server/managers/ApiCacheManager')
 const Auth = require('../../../server/Auth')
 const Logger = require('../../../server/Logger')
+const SocketAuthority = require('../../../server/SocketAuthority')
 
 describe('LibraryItemController', () => {
   /** @type {ApiRouter} */
@@ -299,4 +300,41 @@ describe('LibraryItemController', () => {
       expect(fakeRes.sendStatus.calledWith(403)).to.be.true
     })
   })
+
+  describe('updateTracks', () => {
+    it('recomputes book duration to exclude disabled audio tracks', async () => {
+      const library = await Database.libraryModel.create({ name: 'Tracks Library', mediaType: 'book' })
+      const libraryFolder = await Database.libraryFolderModel.create({ path: '/tracks', libraryId: library.id })
+
+      // Book with two audio tracks (100s + 50s) and a stored duration of 150s
+      const audioFiles = [
+        { index: 1, ino: 'file-1', duration: 100, exclude: false, metadata: { filename: 'track1.mp3', size: 1000 } },
+        { index: 2, ino: 'file-2', duration: 50, exclude: false, metadata: { filename: 'track2.mp3', size: 1000 } }
+      ]
+      const book = await Database.bookModel.create({ title: 'Two Track Book', duration: 150, audioFiles, tags: [], narrators: [], genres: [], chapters: [] })
+      const libraryItem = await Database.libraryItemModel.create({ libraryFiles: [], mediaId: book.id, mediaType: 'book', libraryId: library.id, libraryFolderId: libraryFolder.id })
+
+      sinon.stub(SocketAuthority, 'libraryItemEmitter')
+
+      const expandedLibraryItem = await Database.libraryItemModel.getExpandedById(libraryItem.id)
+      const fakeReq = {
+        libraryItem: expandedLibraryItem,
+        body: {
+          orderedFileData: [
+            { ino: 'file-1', exclude: false },
+            { ino: 'file-2', exclude: true }
+          ]
+        }
+      }
+      const fakeRes = { json: sinon.spy(), sendStatus: sinon.spy() }
+
+      await LibraryItemController.updateTracks.bind(apiRouter)(fakeReq, fakeRes)
+
+      expect(fakeRes.json.calledOnce).to.be.true
+
+      // Duration should now reflect only the enabled track (100s), not the original 150s
+      const updatedBook = await Database.bookModel.findByPk(book.id)
+      expect(updatedBook.duration).to.equal(100)
+    })
+  })
 })