implement message id rfd

Cargo.toml

@@ -22,6 +22,7 @@ unstable = [
     "unstable_session_model",
     "unstable_session_resume",
     "unstable_session_usage",
+    "unstable_message_id",
 ]
 unstable_cancel_request = []
 unstable_session_fork = []
@@ -30,6 +31,7 @@ unstable_session_list = []
 unstable_session_model = []
 unstable_session_resume = []
 unstable_session_usage = []
+unstable_message_id = []
 
 [[bin]]
 name = "generate"

src/agent.rs

@@ -1950,6 +1950,18 @@ impl HttpHeader {
 pub struct PromptRequest {
     /// The ID of the session to send this user message to
     pub session_id: SessionId,
+    /// **UNSTABLE**
+    ///
+    /// This capability is not part of the spec yet, and may be removed or changed at any point.
+    ///
+    /// A client-generated unique identifier for this user message.
+    ///
+    /// If provided, the Agent SHOULD echo this value as `userMessageId` in the
+    /// [`PromptResponse`] to confirm it was recorded.
+    /// Both clients and agents MUST use UUID format for message IDs.
+    #[cfg(feature = "unstable_message_id")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub message_id: Option<String>,
     /// The blocks of content that compose the user's message.
     ///
     /// As a baseline, the Agent MUST support [`ContentBlock::Text`] and [`ContentBlock::ResourceLink`],
@@ -1978,11 +1990,29 @@ impl PromptRequest {
     pub fn new(session_id: impl Into<SessionId>, prompt: Vec<ContentBlock>) -> Self {
         Self {
             session_id: session_id.into(),
+            #[cfg(feature = "unstable_message_id")]
+            message_id: None,
             prompt,
             meta: None,
         }
     }
 
+    /// **UNSTABLE**
+    ///
+    /// This capability is not part of the spec yet, and may be removed or changed at any point.
+    ///
+    /// A client-generated unique identifier for this user message.
+    ///
+    /// If provided, the Agent SHOULD echo this value as `userMessageId` in the
+    /// [`PromptResponse`] to confirm it was recorded.
+    /// Both clients and agents MUST use UUID format for message IDs.
+    #[cfg(feature = "unstable_message_id")]
+    #[must_use]
+    pub fn message_id(mut self, message_id: impl IntoOption<String>) -> Self {
+        self.message_id = message_id.into_option();
+        self
+    }
+
     /// The _meta property is reserved by ACP to allow clients and agents to attach additional
     /// metadata to their interactions. Implementations MUST NOT make assumptions about values at
     /// these keys.
@@ -2003,6 +2033,18 @@ impl PromptRequest {
 #[serde(rename_all = "camelCase")]
 #[non_exhaustive]
 pub struct PromptResponse {
+    /// **UNSTABLE**
+    ///
+    /// This capability is not part of the spec yet, and may be removed or changed at any point.
+    ///
+    /// The acknowledged user message ID.
+    ///
+    /// If the client provided a `messageId` in the [`PromptRequest`], the agent echoes it here
+    /// to confirm it was recorded. If the client did not provide one, the agent MAY assign one
+    /// and return it here. Absence of this field indicates the agent did not record a message ID.
+    #[cfg(feature = "unstable_message_id")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub user_message_id: Option<String>,
     /// Indicates why the agent stopped processing the turn.
     pub stop_reason: StopReason,
     /// **UNSTABLE**
@@ -2026,13 +2068,31 @@ impl PromptResponse {
     #[must_use]
     pub fn new(stop_reason: StopReason) -> Self {
         Self {
+            #[cfg(feature = "unstable_message_id")]
+            user_message_id: None,
             stop_reason,
             #[cfg(feature = "unstable_session_usage")]
             usage: None,
             meta: None,
         }
     }
 
+    /// **UNSTABLE**
+    ///
+    /// This capability is not part of the spec yet, and may be removed or changed at any point.
+    ///
+    /// The acknowledged user message ID.
+    ///
+    /// If the client provided a `messageId` in the [`PromptRequest`], the agent echoes it here
+    /// to confirm it was recorded. If the client did not provide one, the agent MAY assign one
+    /// and return it here. Absence of this field indicates the agent did not record a message ID.
+    #[cfg(feature = "unstable_message_id")]
+    #[must_use]
+    pub fn user_message_id(mut self, user_message_id: impl IntoOption<String>) -> Self {
+        self.user_message_id = user_message_id.into_option();
+        self
+    }
+
     /// **UNSTABLE**
     ///
     /// This capability is not part of the spec yet, and may be removed or changed at any point.

src/client.rs

@@ -330,6 +330,18 @@ impl Cost {
 pub struct ContentChunk {
     /// A single item of content
     pub content: ContentBlock,
+    /// **UNSTABLE**
+    ///
+    /// This capability is not part of the spec yet, and may be removed or changed at any point.
+    ///
+    /// A unique identifier for the message this chunk belongs to.
+    ///
+    /// All chunks belonging to the same message share the same `messageId`.
+    /// A change in `messageId` indicates a new message has started.
+    /// Both clients and agents MUST use UUID format for message IDs.
+    #[cfg(feature = "unstable_message_id")]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub message_id: Option<String>,
     /// The _meta property is reserved by ACP to allow clients and agents to attach additional
     /// metadata to their interactions. Implementations MUST NOT make assumptions about values at
     /// these keys.
@@ -344,10 +356,28 @@ impl ContentChunk {
     pub fn new(content: ContentBlock) -> Self {
         Self {
             content,
+            #[cfg(feature = "unstable_message_id")]
+            message_id: None,
             meta: None,
         }
     }
 
+    /// **UNSTABLE**
+    ///
+    /// This capability is not part of the spec yet, and may be removed or changed at any point.
+    ///
+    /// A unique identifier for the message this chunk belongs to.
+    ///
+    /// All chunks belonging to the same message share the same `messageId`.
+    /// A change in `messageId` indicates a new message has started.
+    /// Both clients and agents MUST use UUID format for message IDs.
+    #[cfg(feature = "unstable_message_id")]
+    #[must_use]
+    pub fn message_id(mut self, message_id: impl IntoOption<String>) -> Self {
+        self.message_id = message_id.into_option();
+        self
+    }
+
     /// The _meta property is reserved by ACP to allow clients and agents to attach additional
     /// metadata to their interactions. Implementations MUST NOT make assumptions about values at
     /// these keys.

src/rpc.rs

@@ -436,6 +436,8 @@ fn test_notification_wire_format() {
                             text: "Hello".to_string(),
                             meta: None,
                         }),
+                        #[cfg(feature = "unstable_message_id")]
+                        message_id: None,
                         meta: None,
                     }),
                     meta: None,