Fix thread/list cwd filtering for Windows verbatim paths (#17414)

Addresses #17302

Problem: `thread/list` compared cwd filters with raw path equality, so
`resume --last` could miss Windows sessions when the saved cwd used a
verbatim path form and the current cwd did not.

Solution: Normalize cwd comparisons through the existing path comparison
utilities before falling back to direct equality, and add Windows
regression coverage for verbatim paths. I made this a general utility
function and replaced all of the duplicated instance of it across the
code base.

codex-rs/utils/path-utils/src/lib.rs

@@ -16,6 +16,19 @@ pub fn normalize_for_path_comparison(path: impl AsRef<Path>) -> std::io::Result<
     Ok(normalize_for_wsl(canonical))
 }
 
+/// Compare paths after applying Codex's filesystem normalization.
+///
+/// If either path cannot be normalized, this falls back to direct path equality.
+pub fn paths_match_after_normalization(left: impl AsRef<Path>, right: impl AsRef<Path>) -> bool {
+    if let (Ok(left), Ok(right)) = (
+        normalize_for_path_comparison(left.as_ref()),
+        normalize_for_path_comparison(right.as_ref()),
+    ) {
+        return left == right;
+    }
+    left.as_ref() == right.as_ref()
+}
+
 pub fn normalize_for_native_workdir(path: impl AsRef<Path>) -> PathBuf {
     normalize_for_native_workdir_with_flag(path.as_ref().to_path_buf(), cfg!(windows))
 }