app-server: expose loaded thread status via read/list and notifications (#11786)

Motivation
- Today, a newly connected client has no direct way to determine the
current runtime status of threads from read/list responses alone.
- This forces clients to infer state from transient events, which can
lead to stale or inconsistent UI when reconnecting or attaching late.

Changes
- Add `status` to `thread/read` responses.
- Add `statuses` to `thread/list` responses.
- Emit `thread/status/changed` notifications with `threadId` and the new
status.
- Track runtime status for all loaded threads and default unknown
threads to `idle`.
- Update protocol/docs/tests/schema fixtures for the revised API.

Testing
- Validated protocol API changes with automated protocol tests and
regenerated schema/type fixtures.
- Validated app-server behavior with unit and integration test suites,
including status transitions and notifications.

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

@@ -794,6 +794,14 @@
           ],
           "description": "Origin of the thread (CLI, VSCode, codex exec, codex app-server, etc.)."
         },
+        "status": {
+          "allOf": [
+            {
+              "$ref": "#/definitions/ThreadStatus"
+            }
+          ],
+          "description": "Current runtime status for the thread."
+        },
         "turns": {
           "description": "Only populated on `thread/resume`, `thread/rollback`, `thread/fork`, and `thread/read` (when `includeTurns` is true) responses. For all other responses and notifications returning a Thread, the turns field will be an empty list.",
           "items": {
@@ -815,11 +823,19 @@
         "modelProvider",
         "preview",
         "source",
+        "status",
         "turns",
         "updatedAt"
       ],
       "type": "object"
     },
+    "ThreadActiveFlag": {
+      "enum": [
+        "waitingOnApproval",
+        "waitingOnUserInput"
+      ],
+      "type": "string"
+    },
     "ThreadId": {
       "type": "string"
     },
@@ -1306,6 +1322,81 @@
         }
       ]
     },
+    "ThreadStatus": {
+      "oneOf": [
+        {
+          "properties": {
+            "type": {
+              "enum": [
+                "notLoaded"
+              ],
+              "title": "NotLoadedThreadStatusType",
+              "type": "string"
+            }
+          },
+          "required": [
+            "type"
+          ],
+          "title": "NotLoadedThreadStatus",
+          "type": "object"
+        },
+        {
+          "properties": {
+            "type": {
+              "enum": [
+                "idle"
+              ],
+              "title": "IdleThreadStatusType",
+              "type": "string"
+            }
+          },
+          "required": [
+            "type"
+          ],
+          "title": "IdleThreadStatus",
+          "type": "object"
+        },
+        {
+          "properties": {
+            "type": {
+              "enum": [
+                "systemError"
+              ],
+              "title": "SystemErrorThreadStatusType",
+              "type": "string"
+            }
+          },
+          "required": [
+            "type"
+          ],
+          "title": "SystemErrorThreadStatus",
+          "type": "object"
+        },
+        {
+          "properties": {
+            "activeFlags": {
+              "items": {
+                "$ref": "#/definitions/ThreadActiveFlag"
+              },
+              "type": "array"
+            },
+            "type": {
+              "enum": [
+                "active"
+              ],
+              "title": "ActiveThreadStatusType",
+              "type": "string"
+            }
+          },
+          "required": [
+            "activeFlags",
+            "type"
+          ],
+          "title": "ActiveThreadStatus",
+          "type": "object"
+        }
+      ]
+    },
     "Turn": {
       "properties": {
         "error": {