core: render remote environment cwd natively (#28152)

## Why

Model-visible `<environment_context>` should match the environment of
the executor, not of the app server.

Stacked on #28146.

## What

- Keep selected environment cwd values as `PathUri` while building
environment context.
- Render cwd text using the path convention represented by the URI, with
the canonical URI as a fallback.
- Preserve compatibility with legacy `TurnContextItem.cwd` values when
reconstructing and diffing context.
- Extend the Wine-backed remote Windows test to assert that the model
sees `powershell` and `C:\windows`.

codex-rs/core/src/codex_thread.rs

@@ -458,7 +458,7 @@ impl CodexThread {
             self.codex
                 .session
                 .record_context_updates_and_set_reference_context_item(turn_context.as_ref())
-                .await;
+                .await?;
         }
         self.codex
             .session