diff --git a/codex-rs/utils/path-uri/src/lib.rs b/codex-rs/utils/path-uri/src/lib.rs
index a788fdc9b4d0..444af1ea28c3 100644
--- a/codex-rs/utils/path-uri/src/lib.rs
+++ b/codex-rs/utils/path-uri/src/lib.rs
@@ -9,6 +9,8 @@ use serde::Deserializer;
 use serde::Serialize;
 use serde::Serializer;
 use std::fmt;
+use std::io;
+use std::path::Path;
 use std::str::FromStr;
 use thiserror::Error;
 use ts_rs::TS;
@@ -25,7 +27,7 @@ pub const FILE_SCHEME: &str = "file";
 ///
 /// `file:` paths retain their URI spelling so they can be parsed independently
 /// of the current host. In particular, `/C:/src` remains ambiguous between a
-/// Windows drive path and a valid POSIX path until [`Self::to_native_path`]
+/// Windows drive path and a valid POSIX path until [`Self::to_abs_path`]
 /// applies the current host's rules. A local POSIX `file:` URI can also retain
 /// percent-encoded non-UTF-8 bytes for lossless native round trips.
 ///
@@ -55,15 +57,27 @@ impl PathUri {
 
     /// Converts an absolute path on the current host to a `file:` URI.
     ///
-    /// On Unix, [`AbsolutePathBuf`]'s absolute-path invariant is sufficient for
-    /// `url` to represent the path. On Windows, conversion can still fail for
-    /// absolute paths whose prefix has no `file:` URI representation, including
-    /// `\\.\` device paths and generic `\\?\` verbatim namespaces. Those cases
-    /// return [`PathUriParseError::InvalidFileUriPath`].
-    pub fn from_file_path(path: &AbsolutePathBuf) -> Result<Self, PathUriParseError> {
-        let url = Url::from_file_path(path.as_path())
-            .map_err(|()| PathUriParseError::InvalidFileUriPath)?;
-        Self::try_from(url)
+    /// On Windows, paths without a URI representation, including `\\.\` device
+    /// paths and generic `\\?\` verbatim namespaces, are reported as invalid
+    /// input.
+    pub fn from_abs_path(path: &AbsolutePathBuf) -> io::Result<Self> {
+        let url = Url::from_file_path(path.as_path()).map_err(|()| {
+            io::Error::new(
+                io::ErrorKind::InvalidInput,
+                PathUriParseError::InvalidFileUriPath,
+            )
+        })?;
+        Self::try_from(url).map_err(|err| io::Error::new(io::ErrorKind::InvalidInput, err))
+    }
+
+    /// Converts a path on the current host to a `file:` URI.
+    ///
+    /// Relative paths and paths without a URI representation are reported as
+    /// invalid input.
+    pub fn from_path(path: impl AsRef<Path>) -> io::Result<Self> {
+        let path = AbsolutePathBuf::from_absolute_path_checked(path)
+            .map_err(|err| io::Error::new(io::ErrorKind::InvalidInput, err))?;
+        Self::from_abs_path(&path)
     }
 
     /// Returns the percent-encoded URI path.
@@ -149,13 +163,15 @@ impl PathUri {
     /// on POSIX or a POSIX root on Windows. Because a `file:` URI does not record
     /// its source operating system, callers should only use this method when the
     /// URI is known to identify a path on the current host.
-    pub fn to_native_path(&self) -> Result<AbsolutePathBuf, PathUriParseError> {
-        let path = self
-            .0
-            .to_file_path()
-            .map_err(|()| PathUriParseError::InvalidFileUriPath)?;
+    pub fn to_abs_path(&self) -> io::Result<AbsolutePathBuf> {
+        let path = self.0.to_file_path().map_err(|()| {
+            io::Error::new(
+                io::ErrorKind::InvalidInput,
+                PathUriParseError::InvalidFileUriPath,
+            )
+        })?;
         AbsolutePathBuf::from_absolute_path_checked(path)
-            .map_err(|_| PathUriParseError::InvalidFileUriPath)
+            .map_err(|err| io::Error::new(io::ErrorKind::InvalidInput, err))
     }
 
     /// Returns a clone of the canonical URL.
@@ -216,7 +232,7 @@ impl<'de> Deserialize<'de> for PathUri {
                     .map_or_else(|| path_error.to_string(), |error| error.to_string()),
             )
         })?;
-        Self::from_file_path(&path).map_err(serde::de::Error::custom)
+        Self::from_abs_path(&path).map_err(serde::de::Error::custom)
     }
 }
 
diff --git a/codex-rs/utils/path-uri/src/tests.rs b/codex-rs/utils/path-uri/src/tests.rs
index 6a237a8c1efc..4fb2ba5b452c 100644
--- a/codex-rs/utils/path-uri/src/tests.rs
+++ b/codex-rs/utils/path-uri/src/tests.rs
@@ -12,7 +12,7 @@ fn file_uri_round_trips_an_absolute_path() {
         .expect("current directory")
         .join("a path/file.rs");
 
-    let uri = PathUri::from_file_path(&path).expect("path should convert to a file URI");
+    let uri = PathUri::from_abs_path(&path).expect("path should convert to a file URI");
 
     let uri_string = uri.to_string();
     assert!(uri_string.starts_with("file:"));
@@ -22,12 +22,26 @@ fn file_uri_round_trips_an_absolute_path() {
         uri
     );
     assert_eq!(
-        uri.to_native_path()
+        uri.to_abs_path()
             .expect("local file URI should convert to a native path"),
         path
     );
 }
 
+#[test]
+fn non_native_uri_io_conversion_is_invalid_input() {
+    #[cfg(unix)]
+    let uri = PathUri::parse("file://server/share/file.txt").expect("valid file URI");
+    #[cfg(windows)]
+    let uri = PathUri::parse("file:///usr/local/file.txt").expect("valid file URI");
+
+    let error = uri
+        .to_abs_path()
+        .expect_err("URI should not be host-native");
+
+    assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
+}
+
 #[test]
 fn file_uri_parses_a_windows_path_on_any_host() {
     let uri = PathUri::parse("file:///C:/Users/Alice%20Smith/src/main.rs")
@@ -52,8 +66,10 @@ fn file_uri_rejects_windows_prefixes_without_a_uri_representation() {
             .expect("Windows namespace path should be absolute");
 
         assert_eq!(
-            PathUri::from_file_path(&path),
-            Err(PathUriParseError::InvalidFileUriPath),
+            PathUri::from_abs_path(&path)
+                .expect_err("Windows namespace path should not convert")
+                .kind(),
+            io::ErrorKind::InvalidInput,
             "converting {native_path}"
         );
     }
@@ -85,9 +101,9 @@ fn file_uri_accepts_non_utf8_posix_paths() {
     let path = PathBuf::from(std::ffi::OsString::from_vec(b"/tmp/non-utf8-\xff".to_vec()));
     let path = AbsolutePathBuf::from_absolute_path_checked(path).expect("absolute POSIX path");
 
-    let uri = PathUri::from_file_path(&path).expect("non-UTF-8 path should convert to a file URI");
+    let uri = PathUri::from_abs_path(&path).expect("non-UTF-8 path should convert to a file URI");
     assert_eq!(
-        uri.to_native_path()
+        uri.to_abs_path()
             .expect("URI should convert to native path"),
         path
     );
@@ -111,10 +127,10 @@ fn file_uri_round_trips_literal_percent_characters() {
 fn file_uri_round_trips_windows_unc_paths() {
     let path = AbsolutePathBuf::from_absolute_path_checked(r"\\server\share\src\main.rs")
         .expect("absolute UNC path");
-    let uri = PathUri::from_file_path(&path).expect("UNC path should convert to a file URI");
+    let uri = PathUri::from_abs_path(&path).expect("UNC path should convert to a file URI");
 
     assert_eq!(uri.encoded_path(), "/share/src/main.rs");
-    assert_eq!(uri.to_native_path().expect("UNC URI should convert"), path);
+    assert_eq!(uri.to_abs_path().expect("UNC URI should convert"), path);
 }
 
 #[test]
@@ -184,10 +200,17 @@ fn path_uri_deserializes_legacy_absolute_paths() {
 
     assert_eq!(
         uri,
-        PathUri::from_file_path(&path).expect("expected file URI")
+        PathUri::from_abs_path(&path).expect("expected file URI")
     );
 }
 
+#[test]
+fn path_uri_rejects_relative_native_paths() {
+    let error = PathUri::from_path("src/lib.rs").expect_err("relative path should be rejected");
+
+    assert_eq!(error.kind(), io::ErrorKind::InvalidInput);
+}
+
 #[test]
 fn path_uri_rejects_legacy_relative_paths_with_absolute_path_guard() {
     let base = AbsolutePathBuf::current_dir().expect("current directory");