Scope runtime workspace roots to execution environments (#32952)

## Why

Multi-environment turns can run against different filesystems, so a single
thread-wide workspace-root list cannot accurately describe every selected
environment.

## What changed

- Add optional `runtimeWorkspaceRoots` to each app-server environment selection.
  Omitted roots default to that environment's `cwd`, while an empty list selects
  no roots.
- Carry environment-native roots through turn selection, model-visible context,
  permission materialization, and tool sandboxing.
- Keep the top-level `runtimeWorkspaceRoots` field as a compatibility input when
  constructing default environment selections; explicit selections use their
  own roots.

## Testing

- Cover thread and turn API defaults, overrides, empty roots, and schema
  round-tripping.
- Verify foreign roots remain model-visible and remote execution applies the
  target environment's roots before sandbox selection.

GitOrigin-RevId: c6e7a62883c45c676c153055f46a55ee15a323a4

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -4227,13 +4227,15 @@ fn turn_start_params_round_trip_environments() {
     let raw_cwd = r"C:\workspace";
     let cwd: LegacyAppPathString =
         serde_json::from_value(json!(raw_cwd)).expect("API path should deserialize");
+    let workspace_root = cwd.clone();
     let params: TurnStartParams = serde_json::from_value(json!({
         "threadId": "thread_123",
         "input": [],
         "environments": [
             {
                 "environmentId": "local",
-                "cwd": cwd
+                "cwd": cwd,
+                "runtimeWorkspaceRoots": [workspace_root]
             }
         ],
     }))
@@ -4244,6 +4246,7 @@ fn turn_start_params_round_trip_environments() {
         Some(vec![TurnEnvironmentParams {
             environment_id: "local".to_string(),
             cwd: cwd.clone(),
+            runtime_workspace_roots: Some(vec![workspace_root.clone()]),
         }])
     );
     assert_eq!(
@@ -4257,7 +4260,8 @@ fn turn_start_params_round_trip_environments() {
         Some(&json!([
             {
                 "environmentId": "local",
-                "cwd": cwd
+                "cwd": cwd,
+                "runtimeWorkspaceRoots": [workspace_root]
             }
         ]))
     );

codex-rs/app-server-protocol/src/protocol/v2/turn.rs

@@ -41,6 +41,9 @@ pub enum TurnStatus {
 pub struct TurnEnvironmentParams {
     pub environment_id: String,
     pub cwd: LegacyAppPathString,
+    /// Environment-native runtime workspace roots. Omitted defaults to `cwd`.
+    #[ts(optional = nullable)]
+    pub runtime_workspace_roots: Option<Vec<LegacyAppPathString>>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]