Propagate workspace roots to exec-server sandboxes (#32214)

## What changed

- Pass configured workspace roots from core to the exec server so filesystem and process sandbox permissions are materialized against the intended roots.
- Preserve an explicitly empty workspace-root list instead of treating the sandbox working directory as an implicit root.
- Initialize filesystem sandbox contexts with their working directory as the default workspace root.

## Testing

- Add end-to-end coverage for patch and command writes inside and outside workspace roots.
- Verify remote filesystem and process sandboxes do not grant access through an empty workspace-root list.

GitOrigin-RevId: 6684c8f7de50970b45a29e2a6323df954c96f9f6

codex-rs/exec-server/src/fs_sandbox.rs

@@ -72,11 +72,7 @@ impl FileSystemSandboxRunner {
             .iter()
             .map(native_workspace_root)
             .collect::<Result<Vec<_>, _>>()?;
-        let workspace_roots = if native_workspace_roots.is_empty() {
-            std::slice::from_ref(&cwd.native)
-        } else {
-            native_workspace_roots.as_slice()
-        };
+        let workspace_roots = native_workspace_roots.as_slice();
         let native_permissions: PermissionProfile =
             sandbox.permissions.clone().try_into().map_err(|err| {
                 invalid_request(format!("invalid sandbox permission path URI: {err}"))

codex-rs/exec-server/src/process_sandbox.rs

@@ -56,11 +56,7 @@ pub(crate) fn prepare_exec_request(
         .iter()
         .map(|root| native_path(root, "sandbox workspace root"))
         .collect::<Result<Vec<_>, _>>()?;
-    let workspace_roots = if native_workspace_roots.is_empty() {
-        std::slice::from_ref(&native_sandbox_policy_cwd)
-    } else {
-        native_workspace_roots.as_slice()
-    };
+    let workspace_roots = native_workspace_roots.as_slice();
     let permissions = permissions.materialize_project_roots_with_workspace_roots(workspace_roots);
     let managed_mitm_ca_trust_bundle_path = params.managed_network.as_ref().and_then(|_| {
         CUSTOM_CA_ENV_KEYS.iter().find_map(|key| {