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/tests/common/mcp_process.rs

@@ -50,6 +50,7 @@ use codex_app_server_protocol::SendUserTurnParams;
 use codex_app_server_protocol::ServerRequest;
 use codex_app_server_protocol::SetDefaultModelParams;
 use codex_app_server_protocol::ThreadArchiveParams;
+use codex_app_server_protocol::ThreadCompactStartParams;
 use codex_app_server_protocol::ThreadForkParams;
 use codex_app_server_protocol::ThreadListParams;
 use codex_app_server_protocol::ThreadLoadedListParams;
@@ -418,6 +419,15 @@ impl McpProcess {
         self.send_request("thread/unarchive", params).await
     }
 
+    /// Send a `thread/compact/start` JSON-RPC request.
+    pub async fn send_thread_compact_start_request(
+        &mut self,
+        params: ThreadCompactStartParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("thread/compact/start", params).await
+    }
+
     /// Send a `thread/rollback` JSON-RPC request.
     pub async fn send_thread_rollback_request(
         &mut self,