feat: move exec-server ownership (#16344)

This introduces session-scoped ownership for exec-server so ws
disconnects no longer immediately kill running remote exec processes,
and it prepares the protocol for reconnect-based resume.
- add session_id / resume_session_id to the exec-server initialize
handshake
  - move process ownership under a shared session registry
- detach sessions on websocket disconnect and expire them after a TTL
instead of killing processes immediately (we will resume based on this)
- allow a new connection to resume an existing session and take over
notifications/ownership
- I use UUID to make them not predictable as we don't have auth for now
- make detached-session expiry authoritative at resume time so teardown
wins at the TTL boundary
- reject long-poll process/read calls that get resumed out from under an
older attachment

---------

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

codex-rs/exec-server/src/server/registry.rs

@@ -30,18 +30,18 @@ use crate::server::ExecServerHandler;
 
 pub(crate) fn build_router() -> RpcRouter<ExecServerHandler> {
     let mut router = RpcRouter::new();
-    router.request(
-        INITIALIZE_METHOD,
-        |handler: Arc<ExecServerHandler>, _params: InitializeParams| async move {
-            handler.initialize()
-        },
-    );
     router.notification(
         INITIALIZED_METHOD,
         |handler: Arc<ExecServerHandler>, _params: serde_json::Value| async move {
             handler.initialized()
         },
     );
+    router.request(
+        INITIALIZE_METHOD,
+        |handler: Arc<ExecServerHandler>, params: InitializeParams| async move {
+            handler.initialize(params).await
+        },
+    );
     router.request(
         EXEC_METHOD,
         |handler: Arc<ExecServerHandler>, params: ExecParams| async move { handler.exec(params).await },