fix(settings): harden locations and site login matching

src/utils/downloadLocations.test.ts

@@ -11,9 +11,11 @@ vi.mock('@tauri-apps/api/path', () => ({
 import {
   downloadLocationEquals,
   DEFAULT_CATEGORY_SUBFOLDERS,
+  formatDerivedCategoryPath,
   normalizeCategorySubfolder,
   normalizeDownloadLocationSettings,
-  resolveCategoryDestination
+  resolveCategoryDestination,
+  subfolderFromDerivedCategoryPath
 } from './downloadLocations';
 
 describe('download locations', () => {
@@ -68,4 +70,21 @@ describe('download locations', () => {
     expect(normalizeCategorySubfolder('C:\\Media\\Movies', 'Movies')).toBe('Media/Movies');
     expect(normalizeCategorySubfolder('../../', 'Movies')).toBe('Movies');
   });
+
+  it('formats and parses derived category paths with platform path separators', () => {
+    expect(formatDerivedCategoryPath('/Users/test/Downloads', 'Video Files'))
+      .toBe('/Users/test/Downloads/Video Files');
+    expect(formatDerivedCategoryPath('D:\\Downloads', 'Video Files'))
+      .toBe('D:\\Downloads\\Video Files');
+    expect(subfolderFromDerivedCategoryPath(
+      'D:\\Downloads\\Video Files',
+      'd:\\downloads'
+    )).toBe('Video Files');
+    expect(subfolderFromDerivedCategoryPath(
+      '/Users/test/Downloads/Video Files',
+      '/Users/test/Downloads'
+    )).toBe('Video Files');
+    expect(subfolderFromDerivedCategoryPath('/Volumes/Media', '/Users/test/Downloads'))
+      .toBeNull();
+  });
 });

src/utils/downloadLocations.ts

@@ -61,6 +61,31 @@ const normalizedForComparison = (value: string): string =>
 const legacyDerivedPath = (base: string, subfolder: string): string =>
   `${normalizedForComparison(base)}/${subfolder.replace(/^[\\/]+|[\\/]+$/g, '')}`;
 
+const isWindowsLikePath = (value: string): boolean =>
+  /^[a-z]:[\\/]/i.test(value) || value.startsWith('\\\\') || value.includes('\\');
+
+export const formatDerivedCategoryPath = (base: string, subfolder: string): string => {
+  const trimmedBase = base.trim() || '~/Downloads';
+  const relative = subfolder.replace(/^[\\/]+|[\\/]+$/g, '');
+  const separator = isWindowsLikePath(trimmedBase) ? '\\' : '/';
+  return `${trimmedBase.replace(/[\\/]+$/, '')}${separator}${relative}`;
+};
+
+export const subfolderFromDerivedCategoryPath = (
+  value: string,
+  base: string
+): string | null => {
+  const normalizedValue = normalizedForComparison(value.trim());
+  const normalizedBase = normalizedForComparison((base.trim() || '~/Downloads'));
+  const isWindows = isWindowsLikePath(base);
+  const comparableValue = isWindows ? normalizedValue.toLocaleLowerCase() : normalizedValue;
+  const comparableBase = isWindows ? normalizedBase.toLocaleLowerCase() : normalizedBase;
+
+  if (comparableValue === comparableBase) return '';
+  if (!comparableValue.startsWith(`${comparableBase}/`)) return null;
+  return normalizedValue.slice(normalizedBase.length + 1);
+};
+
 export const normalizeCategorySubfolder = (
   value: string,
   fallback: string