fix: Backslash incorrectly decoded (#3962)

Author: DreierF

packages/router-core/src/path.ts

@@ -348,12 +348,7 @@ function baseParsePathname(
       // Handle regular pathname segment
       return {
         type: SEGMENT_TYPE_PATHNAME,
-        value: partToMatch.includes('%25')
-          ? partToMatch
-              .split('%25')
-              .map((segment) => decodeURI(segment))
-              .join('%25')
-          : decodeURI(partToMatch),
+        value: partToMatch,
       }
     }),
   )

packages/router-core/tests/path.test.ts

@@ -345,6 +345,12 @@ describe('interpolatePath', () => {
         params: { _splat: 'sean/cassiere' },
         result: '/users/sean/cassiere',
       },
+      {
+        name: 'should preserve backslashes in path parameters',
+        path: '/b/$postId',
+        params: { postId: 'test[s\\%2F.\\%2Fparameter]' },
+        result: '/b/test%5Bs%5C%252F.%5C%252Fparameter%5D',
+      },
     ])('$name', ({ path, params, decodeCharMap, result }) => {
       expect(
         interpolatePath({