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/protocol/src/protocol.rs

@@ -773,6 +773,71 @@ pub enum EventMsg {
     AgentMessageContentDelta(AgentMessageContentDeltaEvent),
     ReasoningContentDelta(ReasoningContentDeltaEvent),
     ReasoningRawContentDelta(ReasoningRawContentDeltaEvent),
+
+    /// Collab interaction: agent spawn begin.
+    CollabAgentSpawnBegin(CollabAgentSpawnBeginEvent),
+    /// Collab interaction: agent spawn end.
+    CollabAgentSpawnEnd(CollabAgentSpawnEndEvent),
+    /// Collab interaction: agent interaction begin.
+    CollabAgentInteractionBegin(CollabAgentInteractionBeginEvent),
+    /// Collab interaction: agent interaction end.
+    CollabAgentInteractionEnd(CollabAgentInteractionEndEvent),
+    /// Collab interaction: waiting begin.
+    CollabWaitingBegin(CollabWaitingBeginEvent),
+    /// Collab interaction: waiting end.
+    CollabWaitingEnd(CollabWaitingEndEvent),
+    /// Collab interaction: close begin.
+    CollabCloseBegin(CollabCloseBeginEvent),
+    /// Collab interaction: close end.
+    CollabCloseEnd(CollabCloseEndEvent),
+}
+
+impl From<CollabAgentSpawnBeginEvent> for EventMsg {
+    fn from(event: CollabAgentSpawnBeginEvent) -> Self {
+        EventMsg::CollabAgentSpawnBegin(event)
+    }
+}
+
+impl From<CollabAgentSpawnEndEvent> for EventMsg {
+    fn from(event: CollabAgentSpawnEndEvent) -> Self {
+        EventMsg::CollabAgentSpawnEnd(event)
+    }
+}
+
+impl From<CollabAgentInteractionBeginEvent> for EventMsg {
+    fn from(event: CollabAgentInteractionBeginEvent) -> Self {
+        EventMsg::CollabAgentInteractionBegin(event)
+    }
+}
+
+impl From<CollabAgentInteractionEndEvent> for EventMsg {
+    fn from(event: CollabAgentInteractionEndEvent) -> Self {
+        EventMsg::CollabAgentInteractionEnd(event)
+    }
+}
+
+impl From<CollabWaitingBeginEvent> for EventMsg {
+    fn from(event: CollabWaitingBeginEvent) -> Self {
+        EventMsg::CollabWaitingBegin(event)
+    }
+}
+
+impl From<CollabWaitingEndEvent> for EventMsg {
+    fn from(event: CollabWaitingEndEvent) -> Self {
+        EventMsg::CollabWaitingEnd(event)
+    }
+}
+
+impl From<CollabCloseBeginEvent> for EventMsg {
+    fn from(event: CollabCloseBeginEvent) -> Self {
+        EventMsg::CollabCloseBegin(event)
+    }
+}
+
+impl From<CollabCloseEndEvent> for EventMsg {
+    fn from(event: CollabCloseEndEvent) -> Self {
+        EventMsg::CollabCloseEnd(event)
+    }
 }
 
 /// Agent lifecycle status, derived from emitted events.
@@ -2023,6 +2088,105 @@ pub enum TurnAbortReason {
     ReviewEnded,
 }
 
+#[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,
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;