Add turn-scoped environment selections (#18416)

## Summary
- add experimental turn/start.environments params for per-turn
environment id + cwd selections
- pass selections through core protocol ops and resolve them with
EnvironmentManager before TurnContext creation
- treat omitted selections as default behavior, empty selections as no
environment, and non-empty selections as first environment/cwd as the
turn primary

## Testing
- ran `just fmt`
- ran `just write-app-server-schema`
- not run: unit tests for this stacked PR

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -3706,6 +3706,21 @@
       ],
       "type": "object"
     },
+    "TurnEnvironmentParams": {
+      "properties": {
+        "cwd": {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        },
+        "environmentId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "cwd",
+        "environmentId"
+      ],
+      "type": "object"
+    },
     "TurnInterruptParams": {
       "properties": {
         "threadId": {

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -16260,6 +16260,21 @@
         "title": "TurnDiffUpdatedNotification",
         "type": "object"
       },
+      "TurnEnvironmentParams": {
+        "properties": {
+          "cwd": {
+            "$ref": "#/definitions/v2/AbsolutePathBuf"
+          },
+          "environmentId": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "cwd",
+          "environmentId"
+        ],
+        "type": "object"
+      },
       "TurnError": {
         "properties": {
           "additionalDetails": {

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -14154,6 +14154,21 @@
       "title": "TurnDiffUpdatedNotification",
       "type": "object"
     },
+    "TurnEnvironmentParams": {
+      "properties": {
+        "cwd": {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        },
+        "environmentId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "cwd",
+        "environmentId"
+      ],
+      "type": "object"
+    },
     "TurnError": {
       "properties": {
         "additionalDetails": {

codex-rs/app-server-protocol/schema/json/v2/TurnStartParams.json

@@ -377,6 +377,21 @@
       ],
       "type": "object"
     },
+    "TurnEnvironmentParams": {
+      "properties": {
+        "cwd": {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        },
+        "environmentId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "cwd",
+        "environmentId"
+      ],
+      "type": "object"
+    },
     "UserInput": {
       "oneOf": [
         {

codex-rs/app-server-protocol/schema/typescript/v2/TurnEnvironmentParams.ts

@@ -0,0 +1,6 @@
+// GENERATED CODE! DO NOT MODIFY BY HAND!
+
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+import type { AbsolutePathBuf } from "../AbsolutePathBuf";
+
+export type TurnEnvironmentParams = { environmentId: string, cwd: AbsolutePathBuf, };

codex-rs/app-server-protocol/schema/typescript/v2/index.ts

@@ -372,6 +372,7 @@ export type { ToolsV2 } from "./ToolsV2";
 export type { Turn } from "./Turn";
 export type { TurnCompletedNotification } from "./TurnCompletedNotification";
 export type { TurnDiffUpdatedNotification } from "./TurnDiffUpdatedNotification";
+export type { TurnEnvironmentParams } from "./TurnEnvironmentParams";
 export type { TurnError } from "./TurnError";
 export type { TurnInterruptParams } from "./TurnInterruptParams";
 export type { TurnInterruptResponse } from "./TurnInterruptResponse";