More assistant events (#18032)

Release Notes:

- N/A

crates/telemetry_events/src/telemetry_events.rs

@@ -44,7 +44,6 @@ pub enum AssistantKind {
     Panel,
     Inline,
 }
-
 impl Display for AssistantKind {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(
@@ -58,6 +57,31 @@ impl Display for AssistantKind {
     }
 }
 
+#[derive(Default, Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum AssistantPhase {
+    #[default]
+    Response,
+    Invoked,
+    Accepted,
+    Rejected,
+}
+
+impl Display for AssistantPhase {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            match self {
+                Self::Response => "response",
+                Self::Invoked => "invoked",
+                Self::Accepted => "accepted",
+                Self::Rejected => "rejected",
+            }
+        )
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 #[serde(tag = "type")]
 pub enum Event {
@@ -121,6 +145,8 @@ pub struct AssistantEvent {
     pub conversation_id: Option<String>,
     /// The kind of assistant (Panel, Inline)
     pub kind: AssistantKind,
+    #[serde(default)]
+    pub phase: AssistantPhase,
     /// Name of the AI model used (gpt-4o, claude-3-5-sonnet, etc)
     pub model: String,
     pub response_latency: Option<Duration>,