Add thread/compact v2 (#10445)

- add `thread/compact` as a trigger-only v2 RPC that submits
`Op::Compact` and returns `{}` immediately.
- add v2 compaction e2e coverage for success and invalid/unknown thread
ids, and update protocol schemas/docs.

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

@@ -598,6 +598,30 @@
           "title": "Thread/unarchiveRequest",
           "type": "object"
         },
+        {
+          "properties": {
+            "id": {
+              "$ref": "#/definitions/RequestId"
+            },
+            "method": {
+              "enum": [
+                "thread/compact/start"
+              ],
+              "title": "Thread/compact/startRequestMethod",
+              "type": "string"
+            },
+            "params": {
+              "$ref": "#/definitions/v2/ThreadCompactStartParams"
+            }
+          },
+          "required": [
+            "id",
+            "method",
+            "params"
+          ],
+          "title": "Thread/compact/startRequest",
+          "type": "object"
+        },
         {
           "properties": {
             "id": {
@@ -13855,6 +13879,24 @@
         "title": "ThreadArchiveResponse",
         "type": "object"
       },
+      "ThreadCompactStartParams": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "properties": {
+          "threadId": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "threadId"
+        ],
+        "title": "ThreadCompactStartParams",
+        "type": "object"
+      },
+      "ThreadCompactStartResponse": {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "title": "ThreadCompactStartResponse",
+        "type": "object"
+      },
       "ThreadForkParams": {
         "$schema": "http://json-schema.org/draft-07/schema#",
         "description": "There are two ways to fork a thread: 1. By thread_id: load the thread from disk by thread_id and fork it into a new thread. 2. By path: load the thread from disk by path and fork it into a new thread.\n\nIf using path, the thread_id param will be ignored.\n\nPrefer using thread_id whenever possible.",