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/tui/src/lib.rs

@@ -1524,13 +1524,7 @@ async fn read_latest_turn_context(path: &Path) -> Option<TurnContextItem> {
 }
 
 pub(crate) fn cwds_differ(current_cwd: &Path, session_cwd: &Path) -> bool {
-    match (
-        path_utils::normalize_for_path_comparison(current_cwd),
-        path_utils::normalize_for_path_comparison(session_cwd),
-    ) {
-        (Ok(current), Ok(session)) => current != session,
-        _ => current_cwd != session_cwd,
-    }
+    !path_utils::paths_match_after_normalization(current_cwd, session_cwd)
 }
 
 pub(crate) enum ResolveCwdOutcome {

codex-rs/tui/src/resume_picker.rs

@@ -1148,13 +1148,7 @@ fn thread_list_params(
 }
 
 fn paths_match(a: &Path, b: &Path) -> bool {
-    if let (Ok(ca), Ok(cb)) = (
-        path_utils::normalize_for_path_comparison(a),
-        path_utils::normalize_for_path_comparison(b),
-    ) {
-        return ca == cb;
-    }
-    a == b
+    path_utils::paths_match_after_normalization(a, b)
 }
 
 #[cfg_attr(not(test), allow(dead_code))]