feat: emit events around collab tools (#9095)

Emit the following events around the collab tools. On the `app-server`
this will be under `item/started` and `item/completed`
```
#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabAgentSpawnBeginEvent {
    /// Identifier for the collab tool call.
    pub call_id: String,
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Initial prompt sent to the agent. Can be empty to prevent CoT leaking at the
    /// beginning.
    pub prompt: String,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabAgentSpawnEndEvent {
    /// Identifier for the collab tool call.
    pub call_id: String,
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the newly spawned agent, if it was created.
    pub new_thread_id: Option<ThreadId>,
    /// Initial prompt sent to the agent. Can be empty to prevent CoT leaking at the
    /// beginning.
    pub prompt: String,
    /// Last known status of the new agent reported to the sender agent.
    pub status: AgentStatus,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabAgentInteractionBeginEvent {
    /// Identifier for the collab tool call.
    pub call_id: String,
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the receiver.
    pub receiver_thread_id: ThreadId,
    /// Prompt sent from the sender to the receiver. Can be empty to prevent CoT
    /// leaking at the beginning.
    pub prompt: String,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabAgentInteractionEndEvent {
    /// Identifier for the collab tool call.
    pub call_id: String,
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the receiver.
    pub receiver_thread_id: ThreadId,
    /// Prompt sent from the sender to the receiver. Can be empty to prevent CoT
    /// leaking at the beginning.
    pub prompt: String,
    /// Last known status of the receiver agent reported to the sender agent.
    pub status: AgentStatus,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabWaitingBeginEvent {
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the receiver.
    pub receiver_thread_id: ThreadId,
    /// ID of the waiting call.
    pub call_id: String,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabWaitingEndEvent {
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the receiver.
    pub receiver_thread_id: ThreadId,
    /// ID of the waiting call.
    pub call_id: String,
    /// Last known status of the receiver agent reported to the sender agent.
    pub status: AgentStatus,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabCloseBeginEvent {
    /// Identifier for the collab tool call.
    pub call_id: String,
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the receiver.
    pub receiver_thread_id: ThreadId,
}

#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, JsonSchema, TS)]
pub struct CollabCloseEndEvent {
    /// Identifier for the collab tool call.
    pub call_id: String,
    /// Thread ID of the sender.
    pub sender_thread_id: ThreadId,
    /// Thread ID of the receiver.
    pub receiver_thread_id: ThreadId,
    /// Last known status of the receiver agent reported to the sender agent before
    /// the close.
    pub status: AgentStatus,
}
```

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -571,6 +571,16 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             EventMsg::ContextCompacted(_) => {
                 ts_msg!(self, "context compacted");
             }
+            EventMsg::CollabAgentSpawnBegin(_)
+            | EventMsg::CollabAgentSpawnEnd(_)
+            | EventMsg::CollabAgentInteractionBegin(_)
+            | EventMsg::CollabAgentInteractionEnd(_)
+            | EventMsg::CollabWaitingBegin(_)
+            | EventMsg::CollabWaitingEnd(_)
+            | EventMsg::CollabCloseBegin(_)
+            | EventMsg::CollabCloseEnd(_) => {
+                // TODO(jif) handle collab tools.
+            }
             EventMsg::ShutdownComplete => return CodexStatus::Shutdown,
             EventMsg::WebSearchBegin(_)
             | EventMsg::ExecApprovalRequest(_)