feat: add wait tool implementation for collab (#9088)

Add implementation for the `wait` tool.

For this we consider all status different from `PendingInit` and
`Running` as terminal. The `wait` tool call will return either after a
given timeout or when the tool reaches a non-terminal status.

A few points to note:
* The usage of a channel is preferred to prevent some races (just
looping on `get_status()` could "miss" a terminal status)
* The order of operations is very important, we need to first subscribe
and then check the last known status to prevent race conditions
* If the channel gets dropped, we return an error on purpose

codex-rs/core/src/codex_thread.rs

@@ -5,6 +5,7 @@ use crate::protocol::Event;
 use crate::protocol::Op;
 use crate::protocol::Submission;
 use std::path::PathBuf;
+use tokio::sync::watch;
 
 pub struct CodexThread {
     codex: Codex,
@@ -38,6 +39,10 @@ impl CodexThread {
         self.codex.agent_status().await
     }
 
+    pub(crate) fn subscribe_status(&self) -> watch::Receiver<AgentStatus> {
+        self.codex.agent_status.clone()
+    }
+
     pub fn rollout_path(&self) -> PathBuf {
         self.rollout_path.clone()
     }