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/path_utils_tests.rs

@@ -78,3 +78,38 @@ mod native_workdir {
         assert_eq!(normalized, path);
     }
 }
+
+mod path_comparison {
+    use super::super::paths_match_after_normalization;
+    use std::path::PathBuf;
+
+    #[test]
+    fn matches_identical_existing_paths() -> std::io::Result<()> {
+        let dir = tempfile::tempdir()?;
+
+        assert!(paths_match_after_normalization(dir.path(), dir.path()));
+        Ok(())
+    }
+
+    #[test]
+    fn falls_back_to_raw_equality_when_paths_cannot_be_normalized() {
+        assert!(paths_match_after_normalization(
+            PathBuf::from("missing"),
+            PathBuf::from("missing"),
+        ));
+        assert!(!paths_match_after_normalization(
+            PathBuf::from("missing-a"),
+            PathBuf::from("missing-b"),
+        ));
+    }
+
+    #[cfg(windows)]
+    #[test]
+    fn matches_windows_verbatim_paths() -> std::io::Result<()> {
+        let dir = tempfile::tempdir()?;
+        let verbatim_dir = PathBuf::from(format!(r"\\?\{}", dir.path().display()));
+
+        assert!(paths_match_after_normalization(verbatim_dir, dir.path()));
+        Ok(())
+    }
+}