fix(scanner): resolve case-insensitive path identity to prevent duplicate books

When library items are scanned or moved on case-insensitive filesystems, paths with non-standard author or folder capitalization point to the same physical disk entries. Treating previous path spellings as distinct caused scanner, upload, dock, and rename services to fail path-reuse lookups and create duplicate book records.

Introduce path identity helpers to check whether paths resolve to the same underlying filesystem entry, treating matching entries as path updates rather than creating duplicate books.

Closes #1012

server/src/modules/upload/upload.service.test.ts

@@ -1,6 +1,6 @@
 vi.mock('fs/promises', async () => {
   const actual = await vi.importActual('fs/promises');
-  return { ...actual, access: vi.fn(), stat: vi.fn() };
+  return { ...actual, access: vi.fn(), lstat: vi.fn(), readdir: vi.fn(), stat: vi.fn() };
 });
 
 vi.mock('../scanner/lib/hash', () => ({ computeFileHash: vi.fn() }));
@@ -10,7 +10,7 @@ vi.mock('../metadata/lib/cbz-metadata', () => ({ extractCbzMetadata: vi.fn(), ex
 vi.mock('../metadata/lib/mobi-parser', () => ({ parseMobiFile: vi.fn() }));
 vi.mock('../metadata/lib/pdf-parser', () => ({ parsePdfFile: vi.fn() }));
 
-import { access as fsAccess, stat } from 'fs/promises';
+import { access as fsAccess, lstat, readdir, stat } from 'fs/promises';
 import { BadRequestException, ConflictException, ForbiddenException, Logger, NotFoundException, ServiceUnavailableException } from '@nestjs/common';
 import { extractEpubMetadata } from '../metadata/lib/epub';
 import { extractCbzMetadata } from '../metadata/lib/cbz-metadata';
@@ -22,6 +22,8 @@ import { books } from '../../db/schema';
 import { UploadService } from './upload.service';
 
 const mockFsAccess = fsAccess as MockedFunction<typeof fsAccess>;
+const mockLstat = lstat as MockedFunction<typeof lstat>;
+const mockReaddir = readdir as MockedFunction<typeof readdir>;
 const mockStat = stat as MockedFunction<typeof stat>;
 const mockExtractEpubMetadata = extractEpubMetadata as MockedFunction<typeof extractEpubMetadata>;
 const mockExtractCbzMetadata = extractCbzMetadata as MockedFunction<typeof extractCbzMetadata>;
@@ -133,6 +135,8 @@ describe('UploadService', () => {
     appSettings.getUploadPatternBookPerFolder.mockResolvedValue(null);
     appSettings.isCrossPlatformPathSanitizationEnabled.mockResolvedValue(false);
     mockFsAccess.mockRejectedValue(Object.assign(new Error('not found'), { code: 'ENOENT' }));
+    mockLstat.mockRejectedValue(Object.assign(new Error('not found'), { code: 'ENOENT' }));
+    mockReaddir.mockResolvedValue([]);
     mockExtractEpubMetadata.mockResolvedValue(null);
 
     // addFileToBook defaults
@@ -201,6 +205,50 @@ describe('UploadService', () => {
     expect(processor.processNewBookImportAsync).toHaveBeenCalledWith(99, 1, '/library/Frank Herbert/Dune.epub', 'epub');
   });
 
+  it('stores the directory-entry spelling when an upload targets a case-insensitive parent path', async () => {
+    db.select
+      .mockReturnValueOnce(selectChain([{ id: 1, allowedFormats: ['epub'], fileNamingPattern: '{authors:first}/{title}.{extension}' }]))
+      .mockReturnValueOnce(selectChain([{ id: 2, libraryId: 1, path: '/library' }]));
+    mockExtractEpubMetadata.mockResolvedValue({
+      title: 'Dune',
+      subtitle: null,
+      publisher: null,
+      publishedYear: null,
+      language: null,
+      seriesName: null,
+      seriesIndex: null,
+      isbn13: null,
+      authors: [{ name: 'Bell Hooks' }],
+      tags: [],
+      description: null,
+      isbn10: null,
+    });
+    mockLstat.mockResolvedValue({} as never);
+    mockReaddir.mockImplementation((path) => {
+      const entriesByPath: Record<string, string[]> = {
+        '/': ['library'],
+        '/library': ['bell hooks'],
+        '/library/bell hooks': ['Dune.epub'],
+      };
+      return Promise.resolve(entriesByPath[String(path)] ?? []) as never;
+    });
+
+    await service.upload(1, 2, 'raw.epub', {} as any, user);
+
+    expect(mockReaddir.mock.calls.map((call) => call[0])).toEqual(['/library', '/library/bell hooks']);
+    expect(storage.moveToPath).toHaveBeenCalledWith('/tmp/upload.bin', '/library/Bell Hooks/Dune.epub');
+    expect(processor.createBookRecord).toHaveBeenCalledWith(
+      1,
+      2,
+      '/library/bell hooks',
+      '/library/bell hooks/Dune.epub',
+      'bell hooks/Dune.epub',
+      'epub',
+      456,
+    );
+    expect(processor.processNewBookImportAsync).toHaveBeenCalledWith(99, 1, '/library/bell hooks/Dune.epub', 'epub');
+  });
+
   it('only extracts metadata when an upload adds a file to an existing book', async () => {
     processor.createBookRecord.mockResolvedValue({ bookId: 99, created: false });
     db.select