feat(agents): add watchdog and forked-agent support

Add watchdog scheduling and forked-agent spawn/resume support across the agent control plane, schemas, rollout metadata, and TUI surfaces.

Rolls up follow-up fixes for watchdog lifecycle behavior and guidance: helper cleanup/one-shot enforcement, wait semantics for watchdog check-in agents, and clarified tool descriptions so models align with runtime behavior.

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

@@ -1286,6 +1286,14 @@
       ],
       "type": "object"
     },
+    "CollabAgentSpawnMode": {
+      "enum": [
+        "spawn",
+        "fork",
+        "watchdog"
+      ],
+      "type": "string"
+    },
     "CommandExecutionApprovalDecision": {
       "oneOf": [
         {
@@ -3844,6 +3852,15 @@
               ],
               "description": "Thread ID of the sender."
             },
+            "spawn_mode": {
+              "allOf": [
+                {
+                  "$ref": "#/definitions/CollabAgentSpawnMode"
+                }
+              ],
+              "default": "spawn",
+              "description": "Spawn mode used for this agent."
+            },
             "status": {
               "allOf": [
                 {