diff --git a/codex-rs/utils/path-uri/src/api_path_string.rs b/codex-rs/utils/path-uri/src/api_path_string.rs
index bc63990679..2a8f4564d2 100644
--- a/codex-rs/utils/path-uri/src/api_path_string.rs
+++ b/codex-rs/utils/path-uri/src/api_path_string.rs
@@ -30,7 +30,7 @@ use ts_rs::TS;
 /// `String` and is instead encouraged to convert through [`PathUri`] or
 /// [`AbsolutePathBuf`]. Relative path text remains valid until an operation
 /// such as [`Self::to_path_uri`] requires an absolute path.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, Deserialize, TS)]
+#[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Deserialize, TS)]
 #[serde(transparent)]
 #[ts(type = "string")]
 pub struct LegacyAppPathString(String);
@@ -81,6 +81,28 @@ impl LegacyAppPathString {
         })
     }
 
+    /// Parses this API string as an absolute path native to the current host.
+    ///
+    /// Host-specific path namespaces are normalized before the path is converted
+    /// to a URI. Relative and foreign-platform paths are rejected.
+    pub fn to_host_path_uri(&self) -> Result<PathUri, LegacyAppPathStringError> {
+        self.to_path_uri(PathConvention::native())
+    }
+
+    /// Parses this API string as an absolute path native to the current host.
+    ///
+    /// Host-specific path namespaces are normalized. Relative and
+    /// foreign-platform paths are rejected.
+    pub fn to_host_abs_path(&self) -> Result<AbsolutePathBuf, LegacyAppPathStringError> {
+        let convention = PathConvention::native();
+        self.to_path_uri(convention)?.to_abs_path().map_err(|_| {
+            LegacyAppPathStringError::InvalidNativePath {
+                path: self.0.clone(),
+                convention: Some(convention),
+            }
+        })
+    }
+
     /// Parses this API string as an absolute path using the convention inferred from its spelling.
     pub fn to_inferred_path_uri(&self) -> Option<PathUri> {
         PathUri::try_from(self.clone()).ok()
diff --git a/codex-rs/utils/path-uri/src/lib.rs b/codex-rs/utils/path-uri/src/lib.rs
index ccc9cfd79b..5686ddea24 100644
--- a/codex-rs/utils/path-uri/src/lib.rs
+++ b/codex-rs/utils/path-uri/src/lib.rs
@@ -263,24 +263,50 @@ impl PathUri {
         if self.0.host_str() != base.0.host_str() {
             return false;
         }
-
-        let Some(path_segments) = containment_path_segments(
-            &self.0,
-            self.infer_path_convention()
-                .unwrap_or(PathConvention::Posix),
-        ) else {
+        let Some(convention) = self.infer_path_convention() else {
             return false;
         };
-        let Some(base_segments) = containment_path_segments(
-            &base.0,
-            base.infer_path_convention()
-                .unwrap_or(PathConvention::Posix),
-        ) else {
+        if base.infer_path_convention() != Some(convention) {
+            return false;
+        }
+
+        let Some(path_segments) = containment_path_segments(&self.0, convention) else {
+            return false;
+        };
+        let Some(base_segments) = containment_path_segments(&base.0, convention) else {
             return false;
         };
         path_segments.starts_with(&base_segments)
     }
 
+    /// Returns this path relative to `base` using `/` as the separator.
+    ///
+    /// Both paths are compared lexically in URI space, without consulting the
+    /// host filesystem. `None` is returned when the paths use different native
+    /// conventions or authorities, when this path is outside `base`, or when an
+    /// encoded native separator makes containment ambiguous.
+    pub fn relative_path_from(&self, base: &Self) -> Option<String> {
+        if self == base {
+            return Some(String::new());
+        }
+
+        let convention = self.infer_path_convention()?;
+        if base.infer_path_convention()? != convention || self.0.host_str() != base.0.host_str() {
+            return None;
+        }
+
+        let path_segments = containment_path_segments(&self.0, convention)?;
+        let base_segments = containment_path_segments(&base.0, convention)?;
+        let relative_segments = path_segments.strip_prefix(base_segments.as_slice())?;
+        Some(
+            relative_segments
+                .iter()
+                .map(|segment| decode_uri_path(segment))
+                .collect::<Vec<_>>()
+                .join("/"),
+        )
+    }
+
     /// Lexically resolves native absolute or relative path text against this URI.
     ///
     /// Path text is interpreted using the POSIX or Windows convention inferred