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/thread-store/src/live_thread.rs

@@ -125,7 +125,7 @@ impl LiveThread {
                 }
             }
         }
-        let metadata_sync = ThreadMetadataSync::for_resume(&params);
+        let metadata_sync = ThreadMetadataSync::for_resume(&params)?;
         Ok(Self {
             thread_id,
             thread_store,
@@ -151,7 +151,7 @@ impl LiveThread {
             .metadata_sync
             .lock()
             .await
-            .observe_appended_items(canonical_items.as_slice());
+            .observe_appended_items(canonical_items.as_slice())?;
         if let Some(update) = update {
             self.thread_store
                 .update_thread_metadata(UpdateThreadMetadataParams {