Rust: expose prompt-event observer configuration

rust/src/types.rs

@@ -2235,9 +2235,18 @@ pub struct SessionConfig {
     /// server OAuth requests with host-acquired token data or cancellation.
     pub mcp_auth_handler: Option<Arc<dyn McpAuthHandler>>,
     /// Optional handler for the legacy question-and-answer `ask_user` variant.
-    /// When `None`, `requestUserInput: false` goes on the wire, so this client
-    /// cannot handle legacy user-input requests.
+    /// When `None`,
+    /// `requestUserInput: false` goes on the wire. Enable
+    /// [`observe_prompt_events`](Self::observe_prompt_events) to answer through events instead.
     pub user_input_handler: Option<Arc<dyn UserInputHandler>>,
+    /// Observe pending prompt events with their runtime request IDs.
+    ///
+    /// An event-driven host can answer `user_input.requested` through
+    /// `session.rpc().ui().handle_pending_user_input(...)` and retire its UI on
+    /// `user_input.completed`, including when another client answered.
+    /// Without a callback handler, the observer is responsible for answering;
+    /// otherwise the request can remain pending.
+    pub observe_prompt_events: Option<bool>,
     /// Optional exit-plan-mode handler. When `None`,
     /// `requestExitPlanMode: false` goes on the wire.
     pub exit_plan_mode_handler: Option<Arc<dyn ExitPlanModeHandler>>,
@@ -2307,6 +2316,7 @@ impl std::fmt::Debug for SessionConfig {
             .field("reasoning_summary", &self.reasoning_summary)
             .field("context_tier", &self.context_tier)
             .field("streaming", &self.streaming)
+            .field("observe_prompt_events", &self.observe_prompt_events)
             .field("system_message", &self.system_message)
             .field("ask_user_variant", &self.ask_user_variant)
             .field("tools", &self.tools)
@@ -2522,6 +2532,7 @@ impl Default for SessionConfig {
             elicitation_handler: None,
             mcp_auth_handler: None,
             user_input_handler: None,
+            observe_prompt_events: None,
             exit_plan_mode_handler: None,
             auto_mode_switch_handler: None,
             hooks_handler: None,
@@ -2652,6 +2663,7 @@ impl SessionConfig {
             enable_session_store: self.enable_session_store,
             enable_skills: self.enable_skills,
             request_user_input,
+            observe_prompt_events: self.observe_prompt_events,
             request_permission: permission_active,
             request_exit_plan_mode,
             request_auto_mode_switch,
@@ -2753,6 +2765,12 @@ impl SessionConfig {
         self
     }
 
+    /// Enable event-driven prompt handling. See [`Self::observe_prompt_events`].
+    pub fn with_observe_prompt_events(mut self, enabled: bool) -> Self {
+        self.observe_prompt_events = Some(enabled);
+        self
+    }
+
     /// Install an [`ExitPlanModeHandler`].
     pub fn with_exit_plan_mode_handler(mut self, handler: Arc<dyn ExitPlanModeHandler>) -> Self {
         self.exit_plan_mode_handler = Some(handler);
@@ -3638,6 +3656,8 @@ pub struct ResumeSessionConfig {
     /// Optional user-input handler. See
     /// [`SessionConfig::user_input_handler`].
     pub user_input_handler: Option<Arc<dyn UserInputHandler>>,
+    /// See [`SessionConfig::observe_prompt_events`].
+    pub observe_prompt_events: Option<bool>,
     /// Optional exit-plan-mode handler. See
     /// [`SessionConfig::exit_plan_mode_handler`].
     pub exit_plan_mode_handler: Option<Arc<dyn ExitPlanModeHandler>>,
@@ -3677,6 +3697,7 @@ impl std::fmt::Debug for ResumeSessionConfig {
             .field("reasoning_summary", &self.reasoning_summary)
             .field("context_tier", &self.context_tier)
             .field("streaming", &self.streaming)
+            .field("observe_prompt_events", &self.observe_prompt_events)
             .field("system_message", &self.system_message)
             .field("ask_user_variant", &self.ask_user_variant)
             .field("tools", &self.tools)
@@ -3895,6 +3916,7 @@ impl ResumeSessionConfig {
             enable_session_store: self.enable_session_store,
             enable_skills: self.enable_skills,
             request_user_input,
+            observe_prompt_events: self.observe_prompt_events,
             request_permission: permission_active,
             request_exit_plan_mode,
             request_auto_mode_switch,
@@ -4046,6 +4068,7 @@ impl ResumeSessionConfig {
             elicitation_handler: None,
             mcp_auth_handler: None,
             user_input_handler: None,
+            observe_prompt_events: None,
             exit_plan_mode_handler: None,
             auto_mode_switch_handler: None,
             hooks_handler: None,
@@ -4090,6 +4113,12 @@ impl ResumeSessionConfig {
         self
     }
 
+    /// Enable event-driven prompt handling. See [`SessionConfig::observe_prompt_events`].
+    pub fn with_observe_prompt_events(mut self, enabled: bool) -> Self {
+        self.observe_prompt_events = Some(enabled);
+        self
+    }
+
     /// Install an [`ExitPlanModeHandler`] for the resumed session.
     pub fn with_exit_plan_mode_handler(mut self, handler: Arc<dyn ExitPlanModeHandler>) -> Self {
         self.exit_plan_mode_handler = Some(handler);
@@ -6224,6 +6253,9 @@ impl Default for ExitPlanModeData {
     }
 }
 
+#[cfg(test)]
+mod prompt_observer_tests;
+
 #[cfg(test)]
 mod tests {
     use std::collections::HashMap;

rust/src/types/prompt_observer_tests.rs

@@ -0,0 +1,45 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+
+#![cfg(test)]
+
+use super::*;
+
+#[test]
+fn omitted_prompt_observation_preserves_create_and_resume_wire_shapes() {
+    let (create, _) = SessionConfig::default().into_wire(None).unwrap();
+    let (resume, _) = ResumeSessionConfig::new(SessionId::from("observer"))
+        .into_wire()
+        .unwrap();
+    for wire in [
+        serde_json::to_value(create).unwrap(),
+        serde_json::to_value(resume).unwrap(),
+    ] {
+        assert!(wire.get("observePromptEvents").is_none());
+        assert_eq!(wire["requestUserInput"], false);
+        assert_eq!(wire["requestPermission"], false);
+        assert_eq!(wire["requestElicitation"], false);
+    }
+}
+
+#[test]
+fn prompt_observation_is_serialized_independently_of_callback_handlers() {
+    for enabled in [true, false] {
+        let (create, _) = SessionConfig::default()
+            .with_observe_prompt_events(enabled)
+            .into_wire(None)
+            .unwrap();
+        let (resume, _) = ResumeSessionConfig::new(SessionId::from("observer"))
+            .with_observe_prompt_events(enabled)
+            .into_wire()
+            .unwrap();
+        for wire in [
+            serde_json::to_value(create).unwrap(),
+            serde_json::to_value(resume).unwrap(),
+        ] {
+            assert_eq!(wire["observePromptEvents"], enabled);
+            assert_eq!(wire["requestUserInput"], false);
+            assert_eq!(wire["requestPermission"], false);
+            assert_eq!(wire["requestElicitation"], false);
+        }
+    }
+}

rust/src/wire.rs

@@ -115,6 +115,8 @@ pub(crate) struct SessionCreateWire {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub enable_skills: Option<bool>,
     pub request_user_input: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub observe_prompt_events: Option<bool>,
     pub request_permission: bool,
     pub request_exit_plan_mode: bool,
     pub request_auto_mode_switch: bool,
@@ -276,6 +278,8 @@ pub(crate) struct SessionResumeWire {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub enable_skills: Option<bool>,
     pub request_user_input: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub observe_prompt_events: Option<bool>,
     pub request_permission: bool,
     pub request_exit_plan_mode: bool,
     pub request_auto_mode_switch: bool,