fix: guard drive-letter fallback with IS_WINDOWS to prevent Unix regression

The fallback path in cwdFromSlug() produced Windows-style `D:/...` paths
on Unix for slugs starting with a single letter (e.g. `D-Workspace-...`).
Gate the drive-letter fallback behind `IS_WINDOWS` so Unix correctly
returns `/D/Workspace/...`.

Also fix the test: make the Windows drive-letter fallback assertion
Windows-only (itWindows) and add a Unix counterpart asserting the
correct `/D/Workspace/project/alpha` result.

Author: yigitkonur

src/__tests__/cwd-from-slug.test.ts

@@ -21,10 +21,15 @@ describe('cwdFromSlug', () => {
     fs.rmSync(base, { recursive: true, force: true });
   });
 
-  it('falls back to drive-letter path format when no candidate exists', () => {
+  itWindows('falls back to drive-letter path format when no candidate exists', () => {
     expect(cwdFromSlug('D-Workspace-project-alpha')).toBe('D:/Workspace/project/alpha');
   });
 
+  it('falls back to Unix path format for drive-letter-like slugs on non-Windows', () => {
+    if (process.platform === 'win32') return;
+    expect(cwdFromSlug('D-Workspace-project-alpha')).toBe('/D/Workspace/project/alpha');
+  });
+
   it('keeps Unix fallback behavior for non-drive slugs', () => {
     expect(cwdFromSlug('Users-alice-my-project')).toBe('/Users/alice/my/project');
   });

src/utils/slug.ts

@@ -61,7 +61,7 @@ export function cwdFromSlug(slug: string): string {
   resolve(0, []);
   if (best) return best;
 
-  if (isDriveSlug) {
+  if (isDriveSlug && IS_WINDOWS) {
     const drive = parts[0].toUpperCase();
     const rest = parts.slice(1).join('/');
     return rest ? `${drive}:/${rest}` : `${drive}:/`;