Add backend remember-context RPC

Load source rollouts, extract visible conversation, persist a hidden remembered-context packet, and expose the v2 thread/remember RPC for UI integration.

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

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

@@ -2923,6 +2923,24 @@
         }
       ]
     },
+    "ThreadRememberParams": {
+      "properties": {
+        "sourceThreadIds": {
+          "items": {
+            "type": "string"
+          },
+          "type": "array"
+        },
+        "threadId": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "sourceThreadIds",
+        "threadId"
+      ],
+      "type": "object"
+    },
     "ThreadResumeParams": {
       "description": "There are three ways to resume a thread: 1. By thread_id: load the thread from disk by thread_id and resume it. 2. By history: instantiate the thread from memory and resume it. 3. By path: load the thread from disk by path and resume it.\n\nThe precedence is: history > path > thread_id. If using history or path, the thread_id param will be ignored.\n\nPrefer using thread_id whenever possible.",
       "properties": {
@@ -3905,6 +3923,30 @@
       "title": "Thread/readRequest",
       "type": "object"
     },
+    {
+      "properties": {
+        "id": {
+          "$ref": "#/definitions/RequestId"
+        },
+        "method": {
+          "enum": [
+            "thread/remember"
+          ],
+          "title": "Thread/rememberRequestMethod",
+          "type": "string"
+        },
+        "params": {
+          "$ref": "#/definitions/ThreadRememberParams"
+        }
+      },
+      "required": [
+        "id",
+        "method",
+        "params"
+      ],
+      "title": "Thread/rememberRequest",
+      "type": "object"
+    },
     {
       "properties": {
         "id": {