diff --git a/core/conversations/src/context.rs b/core/conversations/src/context.rs
index d0c28c8..2e5f65d 100644
--- a/core/conversations/src/context.rs
+++ b/core/conversations/src/context.rs
@@ -6,11 +6,11 @@ use crate::account::LogosAccount;
 use crate::causal_history::MissingMessage;
 use crate::conversation::{Convo, GroupConvo};
 
+use crate::response::{ConvoResponse, ProcessResponse};
 use crate::{DeliveryService, RegistrationService};
 use crate::{
     conversation::{Id, PrivateV1Convo},
     errors::ChatError,
-    inbound::InboundResult,
     inbox::Inbox,
     inbox_v2::InboxV2,
     proto::{EncryptedPayload, EnvelopeV1, Message},
@@ -226,7 +226,7 @@ where
     }
 
     // Decode bytes and send to protocol for processing.
-    pub fn handle_payload(&mut self, payload: &[u8]) -> Result<InboundResult, ChatError> {
+    pub fn handle_payload(&mut self, payload: &[u8]) -> Result<ProcessResponse, ChatError> {
         let env = EnvelopeV1::decode(payload)?;
 
         // TODO: Impl Conversation hinting
@@ -238,24 +238,30 @@ where
             c if self.store.borrow().has_conversation(&c)? => {
                 self.dispatch_to_convo(&c, &env.payload)
             }
-            _ => Ok(InboundResult::default()),
+            _ => Ok(ProcessResponse::Unknown),
         }
     }
 
     // Dispatch encrypted payload to Inbox. The Inbox persists the newly
     // created conversation and consumes the ephemeral key internally.
-    fn dispatch_to_inbox(&mut self, enc_payload_bytes: &[u8]) -> Result<InboundResult, ChatError> {
+    fn dispatch_to_inbox(
+        &mut self,
+        enc_payload_bytes: &[u8],
+    ) -> Result<ProcessResponse, ChatError> {
         // EncryptedPayloads are not used by GroupConvos at this time, else this can be performed in `handle_payload`
         // TODO: (P1) reconcile envelope parsing between Covno and GroupConvo
         let enc_payload = EncryptedPayload::decode(enc_payload_bytes)?;
         let public_key_hex = Inbox::<CS>::extract_ephemeral_key_hex(&enc_payload)?;
         self.inbox
             .handle_frame(enc_payload, &public_key_hex, Rc::clone(&self.store))
+            .map(ProcessResponse::InboxResponse)
     }
 
     // Dispatch encrypted payload to the post-quantum inbox.
-    fn dispatch_to_inbox2(&mut self, payload: &[u8]) -> Result<InboundResult, ChatError> {
-        self.pq_inbox.handle_frame(payload)
+    fn dispatch_to_inbox2(&mut self, payload: &[u8]) -> Result<ProcessResponse, ChatError> {
+        self.pq_inbox
+            .handle_frame(payload)
+            .map(ProcessResponse::InboxResponse)
     }
 
     // Dispatch encrypted payload to its corresponding conversation
@@ -263,14 +269,11 @@ where
         &mut self,
         convo_id: ConversationId,
         enc_payload_bytes: &[u8],
-    ) -> Result<InboundResult, ChatError> {
+    ) -> Result<ProcessResponse, ChatError> {
         let enc_payload = EncryptedPayload::decode(enc_payload_bytes)?;
         let mut convo = self.load_convo(convo_id)?;
         let frame = convo.handle_frame(enc_payload)?;
-        Ok(InboundResult {
-            new_conversation: None,
-            frame,
-        })
+        Ok(ProcessResponse::ConvoResponse(ConvoResponse { frame }))
     }
 
     pub fn create_intro_bundle(&mut self) -> Result<Vec<u8>, ChatError> {
diff --git a/core/conversations/src/conversation.rs b/core/conversations/src/conversation.rs
index cde8042..ed9e828 100644
--- a/core/conversations/src/conversation.rs
+++ b/core/conversations/src/conversation.rs
@@ -3,7 +3,7 @@ mod privatev1;
 
 use crate::{
     DeliveryService,
-    inbound::FrameOutcome,
+    response::FrameOutcome,
     service_traits::KeyPackageProvider,
     types::{AccountId, AddressedEncryptedPayload},
 };
diff --git a/core/conversations/src/conversation/group_v1.rs b/core/conversations/src/conversation/group_v1.rs
index 76bf62a..2ab6ed7 100644
--- a/core/conversations/src/conversation/group_v1.rs
+++ b/core/conversations/src/conversation/group_v1.rs
@@ -22,7 +22,7 @@ use crate::types::AccountId;
 use crate::{
     DeliveryService,
     conversation::{ChatError, ConversationId, Convo, GroupConvo, Id},
-    inbound::{FrameOutcome, Message},
+    response::{FrameOutcome, Message},
     service_traits::KeyPackageProvider,
     types::AddressedEncryptedPayload,
 };
@@ -339,27 +339,30 @@ where
             .process_message(provider, protocol_message)
             .map_err(ChatError::generic)?;
 
-        let messages = match processed.into_content() {
+        match processed.into_content() {
             ProcessedMessageContent::ApplicationMessage(msg) => {
                 let reliable = ReliablePayload::decode(msg.into_bytes().as_slice())?;
-                self.causal.on_receive(&self.convo_id, &reliable);
-                vec![Message {
+                let missing_messages = self.causal.on_receive(&self.convo_id, &reliable);
+                let message = Some(Message {
                     convo_id: Arc::from(self.id()),
                     content: reliable.content.to_vec(),
-                }]
+                });
+                Ok(FrameOutcome {
+                    message,
+                    missing_messages,
+                })
             }
             ProcessedMessageContent::StagedCommitMessage(commit) => {
                 self.mls_group
                     .merge_staged_commit(provider, *commit)
                     .map_err(ChatError::generic)?;
-                vec![]
+                Ok(FrameOutcome::default())
             }
             _ => {
                 // TODO: (P2) Log unknown message type
-                vec![]
+                Ok(FrameOutcome::default())
             }
-        };
-        Ok(FrameOutcome { messages })
+        }
     }
 
     fn remote_id(&self) -> String {
diff --git a/core/conversations/src/conversation/privatev1.rs b/core/conversations/src/conversation/privatev1.rs
index c573dda..04dbc4c 100644
--- a/core/conversations/src/conversation/privatev1.rs
+++ b/core/conversations/src/conversation/privatev1.rs
@@ -16,8 +16,8 @@ use crate::{
     context::ConversationIdOwned,
     conversation::{ChatError, ConversationId, Convo, Id},
     errors::EncryptionError,
-    inbound::{FrameOutcome, Message},
     proto,
+    response::{FrameOutcome, Message},
     types::AddressedEncryptedPayload,
     utils::timestamp_millis,
 };
@@ -201,11 +201,11 @@ impl<S: ConversationStore + RatchetStore> PrivateV1Convo<S> {
         Ok(())
     }
 
-    fn handle_content(&self, bytes: Bytes) -> Vec<Message> {
-        vec![Message {
+    fn handle_content(&self, bytes: Bytes) -> Message {
+        Message {
             convo_id: Arc::from(self.id()),
             content: bytes.into(),
-        }]
+        }
     }
 }
 
@@ -252,11 +252,14 @@ impl<S: ConversationStore + RatchetStore> Convo for PrivateV1Convo<S> {
 
         self.save_ratchet_state(&mut *self.store.borrow_mut())?;
 
-        let messages = match frame_type {
-            FrameType::Content(bytes) => self.handle_content(bytes),
-            FrameType::Placeholder(_) => vec![],
+        let message = match frame_type {
+            FrameType::Content(bytes) => Some(self.handle_content(bytes)),
+            FrameType::Placeholder(_) => None,
         };
-        Ok(FrameOutcome { messages })
+        Ok(FrameOutcome {
+            message,
+            missing_messages: Vec::new(),
+        })
     }
 
     fn remote_id(&self) -> String {
diff --git a/core/conversations/src/inbound.rs b/core/conversations/src/inbound.rs
deleted file mode 100644
index 671f066..0000000
--- a/core/conversations/src/inbound.rs
+++ /dev/null
@@ -1,57 +0,0 @@
-//! Outcome of processing a single inbound payload.
-//!
-//! [`InboundResult`] composes two layers:
-//! - [`FrameOutcome`] captures what processing one frame within a conversation
-//!   produces: today, decrypted messages. As protocol features land, new
-//!   per-conversation observations (e.g. group membership changes) become
-//!   additive fields on `FrameOutcome`.
-//! - [`InboundResult`] wraps a `FrameOutcome` and adds the payload-level
-//!   observations a single frame cannot produce — today, the appearance of
-//!   a new conversation from the peer side.
-
-use storage::ConversationKind;
-
-use crate::context::ConversationIdOwned;
-
-/// Observations a conversation produces from processing one frame.
-#[derive(Debug, Clone, Default)]
-pub struct FrameOutcome {
-    /// User content decrypted from this frame, in protocol order.
-    pub messages: Vec<Message>,
-}
-
-impl FrameOutcome {
-    pub fn is_empty(&self) -> bool {
-        self.messages.is_empty()
-    }
-}
-
-/// Everything one inbound payload produced.
-#[derive(Debug, Clone, Default)]
-pub struct InboundResult {
-    /// A new conversation appeared from this payload, if any.
-    pub new_conversation: Option<NewConversation>,
-    /// Observations from the frame inside this payload.
-    pub frame: FrameOutcome,
-}
-
-impl InboundResult {
-    /// True when the payload produced no observable outcome.
-    pub fn is_empty(&self) -> bool {
-        self.new_conversation.is_none() && self.frame.is_empty()
-    }
-}
-
-/// A conversation newly observed from the peer side.
-#[derive(Debug, Clone)]
-pub struct NewConversation {
-    pub convo_id: ConversationIdOwned,
-    pub kind: ConversationKind,
-}
-
-/// User content decrypted from an inbound payload.
-#[derive(Debug, Clone)]
-pub struct Message {
-    pub convo_id: ConversationIdOwned,
-    pub content: Vec<u8>,
-}
diff --git a/core/conversations/src/inbox/handler.rs b/core/conversations/src/inbox/handler.rs
index 2c418c1..eb53cc6 100644
--- a/core/conversations/src/inbox/handler.rs
+++ b/core/conversations/src/inbox/handler.rs
@@ -13,9 +13,9 @@ use crypto::{PrekeyBundle, SymmetricKey32};
 use crate::context::Introduction;
 use crate::conversation::{ChatError, ConversationId, Convo, Id, PrivateV1Convo};
 use crate::crypto::{CopyBytes, PrivateKey, PublicKey};
-use crate::inbound::{InboundResult, NewConversation};
 use crate::inbox::handshake::InboxHandshake;
 use crate::proto;
+use crate::response::{InboxResponse, NewConversation};
 use crate::types::AddressedEncryptedPayload;
 use crypto::Identity;
 
@@ -124,14 +124,14 @@ impl<S: EphemeralKeyStore> Inbox<S> {
     /// Handles an incoming inbox frame. The caller must provide the ephemeral
     /// private key hex looked up from storage. Persists the created
     /// conversation and consumes the ephemeral key. Returns the
-    /// [`InboundResult`] describing what was observed — for a successful
+    /// [`InboxResponse`] describing what was observed — for a successful
     /// invite, a `new_conversation` and one initial `message`.
     pub fn handle_frame<PS: ConversationStore + RatchetStore>(
         &self,
         enc_payload: EncryptedPayload,
         public_key_hex: &str,
         private_store: Rc<RefCell<PS>>,
-    ) -> Result<InboundResult, ChatError> {
+    ) -> Result<InboxResponse, ChatError> {
         let ephemeral_key = self
             .store
             .borrow()
@@ -158,7 +158,7 @@ impl<S: EphemeralKeyStore> Inbox<S> {
                 };
 
                 let frame = convo.handle_frame(enc_payload)?;
-                if frame.messages.is_empty() {
+                if frame.message.is_none() {
                     return Err(ChatError::Protocol(
                         "expected initial message in invite".into(),
                     ));
@@ -170,9 +170,9 @@ impl<S: EphemeralKeyStore> Inbox<S> {
                 };
                 convo.persist()?;
 
-                InboundResult {
-                    new_conversation: Some(new_conversation),
-                    frame,
+                InboxResponse {
+                    new_conversation,
+                    frame: Some(frame),
                 }
             }
         };
diff --git a/core/conversations/src/inbox_v2.rs b/core/conversations/src/inbox_v2.rs
index 7783975..23e0ef7 100644
--- a/core/conversations/src/inbox_v2.rs
+++ b/core/conversations/src/inbox_v2.rs
@@ -21,7 +21,8 @@ use crate::causal_history::MissingMessage;
 use crate::conversation::GroupConvo;
 use crate::conversation::group_v1::MlsContext;
 use crate::conversation::{GroupV1Convo, Id, IdentityProvider};
-use crate::inbound::{FrameOutcome, InboundResult, NewConversation};
+use crate::response::InboxResponse;
+use crate::response::NewConversation;
 use crate::types::AccountId;
 use crate::utils::{blake2b_hex, hash_size};
 pub struct PqMlsContext {
@@ -155,7 +156,7 @@ where
         )
     }
 
-    pub fn handle_frame(&self, payload_bytes: &[u8]) -> Result<InboundResult, ChatError> {
+    pub fn handle_frame(&self, payload_bytes: &[u8]) -> Result<InboxResponse, ChatError> {
         let inbox_frame = InboxV2Frame::decode(payload_bytes)?;
 
         let Some(payload) = inbox_frame.payload else {
@@ -182,7 +183,10 @@ where
         Ok(())
     }
 
-    fn handle_heavy_invite(&self, invite: GroupV1HeavyInvite) -> Result<InboundResult, ChatError> {
+    fn handle_heavy_invite(
+        &self,
+        invite: GroupV1HeavyInvite,
+    ) -> Result<InboxResponse, ChatError> {
         let (msg_in, _rest) = MlsMessageIn::tls_deserialize_bytes(invite.welcome_bytes.as_slice())?;
 
         let MlsMessageBodyIn::Welcome(welcome) = msg_in.extract() else {
@@ -202,12 +206,12 @@ where
         )?;
         let convo_id = Arc::from(convo.id());
         self.persist_convo(convo)?;
-        Ok(InboundResult {
-            new_conversation: Some(NewConversation {
+        Ok(InboxResponse {
+            new_conversation: NewConversation {
                 convo_id,
                 kind: ConversationKind::GroupV1,
-            }),
-            frame: FrameOutcome::default(),
+            },
+            frame: None,
         })
     }
 
diff --git a/core/conversations/src/lib.rs b/core/conversations/src/lib.rs
index 04f0670..0559bf1 100644
--- a/core/conversations/src/lib.rs
+++ b/core/conversations/src/lib.rs
@@ -4,10 +4,10 @@ mod context;
 mod conversation;
 mod crypto;
 mod errors;
-mod inbound;
 mod inbox;
 mod inbox_v2;
 mod proto;
+mod response;
 mod service_traits;
 mod types;
 mod utils;
@@ -19,7 +19,7 @@ pub use chat_sqlite::StorageConfig;
 pub use context::{Context, ConversationId, ConversationIdOwned, Introduction};
 pub use conversation::GroupConvo;
 pub use errors::ChatError;
-pub use inbound::{FrameOutcome, InboundResult, Message, NewConversation};
+pub use response::{FrameOutcome, InboxResponse, Message, NewConversation, ProcessResponse};
 pub use service_traits::{DeliveryService, IdentityProvider, RegistrationService};
 pub use storage::ConversationKind;
 pub use types::{AccountId, AddressedEnvelope};
diff --git a/core/conversations/src/response.rs b/core/conversations/src/response.rs
new file mode 100644
index 0000000..a6d7de6
--- /dev/null
+++ b/core/conversations/src/response.rs
@@ -0,0 +1,62 @@
+//! Outcome of processing a single inbound payload.
+//!
+//! [`ProcessResponse`] is the tagged sum of what a payload produced, one
+//! variant per dispatch destination (inbox, existing conversation, unknown).
+//! [`FrameOutcome`] captures what processing one frame within a conversation
+//! produces: today, a decrypted message. As protocol features land, new
+//! per-conversation observations become additive fields on `FrameOutcome`.
+//!
+//! [`InboxResponse::frame`] is `None` when the inbox produced a new conversation
+//! without an initial message (V2 invite); `Some` when an initial message was
+//! delivered alongside the invite (V1).
+
+use storage::ConversationKind;
+
+use crate::causal_history::MissingMessage;
+use crate::context::ConversationIdOwned;
+
+/// Observations a conversation produces from processing one frame.
+#[derive(Debug, Clone, Default)]
+pub struct FrameOutcome {
+    /// User content decrypted from this frame, in protocol order.
+    pub message: Option<Message>,
+    /// Causal-history gaps detected from this frame's piggybacked history.
+    /// Empty for protocols without causal history (e.g. PrivateV1) and for
+    /// frames that close no gaps.
+    pub missing_messages: Vec<MissingMessage>,
+}
+
+#[derive(Debug, Clone)]
+pub enum ProcessResponse {
+    InboxResponse(InboxResponse),
+    ConvoResponse(ConvoResponse),
+    Unknown,
+}
+
+#[derive(Debug, Clone)]
+pub struct InboxResponse {
+    /// A new conversation appeared from this payload, if any.
+    pub new_conversation: NewConversation,
+    /// Observations from the frame inside this payload.
+    pub frame: Option<FrameOutcome>,
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct ConvoResponse {
+    /// Observations from the frame inside this payload.
+    pub frame: FrameOutcome,
+}
+
+/// A conversation newly observed from the peer side.
+#[derive(Debug, Clone)]
+pub struct NewConversation {
+    pub convo_id: ConversationIdOwned,
+    pub kind: ConversationKind,
+}
+
+/// User content decrypted from an inbound payload.
+#[derive(Debug, Clone)]
+pub struct Message {
+    pub convo_id: ConversationIdOwned,
+    pub content: Vec<u8>,
+}
diff --git a/core/integration_tests_core/tests/mls_integration.rs b/core/integration_tests_core/tests/mls_integration.rs
index ca69370..1b4126a 100644
--- a/core/integration_tests_core/tests/mls_integration.rs
+++ b/core/integration_tests_core/tests/mls_integration.rs
@@ -2,10 +2,10 @@ use std::ops::{Deref, DerefMut};
 
 use components::{EphemeralRegistry, LocalBroadcaster, MemStore};
 use libchat::{
-    Context, ConversationKind, GroupConvo, InboundResult, Message, NewConversation, hex_trunc,
+    Context, ConversationKind, GroupConvo, Message, NewConversation, ProcessResponse, hex_trunc,
 };
 
-type ResultCallback = Box<dyn Fn(&InboundResult)>;
+type ResultCallback = Box<dyn Fn(&ProcessResponse)>;
 
 // Simple client Functionality for testing
 struct Client {
@@ -18,7 +18,7 @@ struct Client {
 impl Client {
     fn init(
         ctx: Context<LocalBroadcaster, EphemeralRegistry, MemStore>,
-        cb: Option<impl Fn(&InboundResult) + 'static>,
+        cb: Option<impl Fn(&ProcessResponse) + 'static>,
     ) -> Self {
         Client {
             inner: ctx,
@@ -39,10 +39,18 @@ impl Client {
             if let Some(cb) = &self.on_result {
                 cb(&result);
             }
-            if let Some(nc) = result.new_conversation {
-                self.new_conversations.push(nc);
+            match result {
+                ProcessResponse::InboxResponse(r) => {
+                    self.new_conversations.push(r.new_conversation);
+                    if let Some(frame) = r.frame {
+                        self.received_messages.extend(frame.message);
+                    }
+                }
+                ProcessResponse::ConvoResponse(r) => {
+                    self.received_messages.extend(r.frame.message);
+                }
+                ProcessResponse::Unknown => {}
             }
-            self.received_messages.extend(result.frame.messages);
         }
     }
 
@@ -69,22 +77,36 @@ impl DerefMut for Client {
     }
 }
 
+fn print_new_conversation(prefix: &str, nc: &NewConversation) {
+    let cid = hex_trunc(nc.convo_id.as_bytes());
+    println!(
+        "{prefix}      ({cid:?}) [conversation started: {:?}]",
+        nc.kind
+    );
+}
+
+fn print_message(prefix: &str, message: Option<&Message>) {
+    if let Some(msg) = message {
+        let cid = hex_trunc(msg.convo_id.as_bytes());
+        let text = String::from_utf8_lossy(&msg.content);
+        println!("{prefix}      ({cid:?}) {text}");
+    }
+}
+
 // Higher order function to handle printing
 fn pretty_print(prefix: impl Into<String>) -> ResultCallback {
     let prefix = prefix.into();
-    Box::new(move |result: &InboundResult| {
-        if let Some(nc) = &result.new_conversation {
-            let cid = hex_trunc(nc.convo_id.as_bytes());
-            println!(
-                "{prefix}      ({cid:?}) [conversation started: {:?}]",
-                nc.kind
-            );
+    Box::new(move |result: &ProcessResponse| match result {
+        ProcessResponse::InboxResponse(r) => {
+            print_new_conversation(&prefix, &r.new_conversation);
+            if let Some(frame) = &r.frame {
+                print_message(&prefix, frame.message.as_ref());
+            }
         }
-        for msg in &result.frame.messages {
-            let cid = hex_trunc(msg.convo_id.as_bytes());
-            let text = String::from_utf8_lossy(&msg.content);
-            println!("{prefix}      ({cid:?}) {text}");
+        ProcessResponse::ConvoResponse(r) => {
+            print_message(&prefix, r.frame.message.as_ref());
         }
+        ProcessResponse::Unknown => {}
     })
 }
 
diff --git a/core/integration_tests_core/tests/private_integration.rs b/core/integration_tests_core/tests/private_integration.rs
index b29117d..634efd1 100644
--- a/core/integration_tests_core/tests/private_integration.rs
+++ b/core/integration_tests_core/tests/private_integration.rs
@@ -1,10 +1,24 @@
 use chat_sqlite::{ChatStorage, StorageConfig};
-use libchat::{Context, ConversationKind, Introduction};
+use libchat::{Context, ConversationKind, Introduction, ProcessResponse};
 use storage::{ConversationStore, IdentityStore};
 use tempfile::tempdir;
 
 use components::{EphemeralRegistry, LocalBroadcaster};
 
+fn expect_convo_response(result: ProcessResponse) -> libchat::FrameOutcome {
+    match result {
+        ProcessResponse::ConvoResponse(r) => r.frame,
+        other => panic!("expected ConvoResponse, got {other:?}"),
+    }
+}
+
+fn expect_inbox_response(result: ProcessResponse) -> libchat::InboxResponse {
+    match result {
+        ProcessResponse::InboxResponse(r) => r,
+        other => panic!("expected InboxResponse, got {other:?}"),
+    }
+}
+
 fn send_and_verify(
     sender: &mut Context<LocalBroadcaster, EphemeralRegistry, ChatStorage>,
     receiver: &mut Context<LocalBroadcaster, EphemeralRegistry, ChatStorage>,
@@ -14,13 +28,12 @@ fn send_and_verify(
     let payloads = sender.send_content(convo_id, content).unwrap();
     let payload = payloads.first().unwrap();
     let result = receiver.handle_payload(&payload.data).unwrap();
-    assert!(result.new_conversation.is_none());
-    assert_eq!(
-        result.frame.messages.len(),
-        1,
-        "steady-state send should yield one message"
-    );
-    assert_eq!(content, result.frame.messages[0].content.as_slice());
+    let frame = expect_convo_response(result);
+    let msg = frame
+        .message
+        .as_ref()
+        .expect("steady-state send should yield one message");
+    assert_eq!(content, msg.content.as_slice());
 }
 
 #[test]
@@ -42,19 +55,16 @@ fn ctx_integration() {
 
     // Raya receives the invite + initial message
     let payload = payloads.first().unwrap();
-    let initial = raya.handle_payload(&payload.data).unwrap();
-    let new_convo = initial
-        .new_conversation
-        .as_ref()
-        .expect("invite must create a conversation");
+    let initial = expect_inbox_response(raya.handle_payload(&payload.data).unwrap());
+    let new_convo = &initial.new_conversation;
     assert!(matches!(new_convo.kind, ConversationKind::PrivateV1));
-    assert_eq!(
-        initial.frame.messages.len(),
-        1,
-        "invite must include initial message"
-    );
-    assert_eq!(content, initial.frame.messages[0].content);
-    assert_eq!(new_convo.convo_id, initial.frame.messages[0].convo_id);
+    let initial_msg = initial
+        .frame
+        .as_ref()
+        .and_then(|f| f.message.as_ref())
+        .expect("invite must include initial message");
+    assert_eq!(content, initial_msg.content);
+    assert_eq!(new_convo.convo_id, initial_msg.convo_id);
     let raya_convo_id = new_convo.convo_id.clone();
 
     // Exchange messages back and forth
@@ -115,11 +125,8 @@ fn conversation_metadata_persistence() {
     let (_, payloads) = bob.create_private_convo(&intro, b"hi").unwrap();
 
     let payload = payloads.first().unwrap();
-    let result = alice.handle_payload(&payload.data).unwrap();
-    let new_convo = result
-        .new_conversation
-        .as_ref()
-        .expect("invite must create a conversation");
+    let result = expect_inbox_response(alice.handle_payload(&payload.data).unwrap());
+    let new_convo = &result.new_conversation;
     assert!(matches!(new_convo.kind, ConversationKind::PrivateV1));
 
     let convos = alice.store().load_conversations().unwrap();
@@ -140,23 +147,18 @@ fn conversation_full_flow() {
     let (bob_convo_id, payloads) = bob.create_private_convo(&intro, b"hello").unwrap();
 
     let payload = payloads.first().unwrap();
-    let result = alice.handle_payload(&payload.data).unwrap();
-    let alice_convo_id = result
-        .new_conversation
-        .as_ref()
-        .expect("invite must create a conversation")
-        .convo_id
-        .clone();
+    let result = expect_inbox_response(alice.handle_payload(&payload.data).unwrap());
+    let alice_convo_id = result.new_conversation.convo_id.clone();
 
     let payloads = alice.send_content(&alice_convo_id, b"reply 1").unwrap();
     let payload = payloads.first().unwrap();
-    let result = bob.handle_payload(&payload.data).unwrap();
-    assert_eq!(result.frame.messages[0].content, b"reply 1");
+    let frame = expect_convo_response(bob.handle_payload(&payload.data).unwrap());
+    assert_eq!(frame.message.unwrap().content, b"reply 1");
 
     let payloads = bob.send_content(&bob_convo_id, b"reply 2").unwrap();
     let payload = payloads.first().unwrap();
-    let result = alice.handle_payload(&payload.data).unwrap();
-    assert_eq!(result.frame.messages[0].content, b"reply 2");
+    let frame = expect_convo_response(alice.handle_payload(&payload.data).unwrap());
+    assert_eq!(frame.message.unwrap().content, b"reply 2");
 
     // Verify conversation list
     let convo_ids = alice.list_conversations().unwrap();
@@ -165,12 +167,12 @@ fn conversation_full_flow() {
     // Continue exchanging messages
     let payloads = bob.send_content(&bob_convo_id, b"more messages").unwrap();
     let payload = payloads.first().unwrap();
-    let result = alice.handle_payload(&payload.data).expect("should decrypt");
-    assert_eq!(result.frame.messages[0].content, b"more messages");
+    let frame = expect_convo_response(alice.handle_payload(&payload.data).expect("should decrypt"));
+    assert_eq!(frame.message.unwrap().content, b"more messages");
 
     // Alice can also send back
     let payloads = alice.send_content(&alice_convo_id, b"alice reply").unwrap();
     let payload = payloads.first().unwrap();
-    let result = bob.handle_payload(&payload.data).unwrap();
-    assert_eq!(result.frame.messages[0].content, b"alice reply");
+    let frame = expect_convo_response(bob.handle_payload(&payload.data).unwrap());
+    assert_eq!(frame.message.unwrap().content, b"alice reply");
 }
diff --git a/crates/client/src/client.rs b/crates/client/src/client.rs
index 5c72876..7c0f923 100644
--- a/crates/client/src/client.rs
+++ b/crates/client/src/client.rs
@@ -1,6 +1,6 @@
 use libchat::{
     AddressedEnvelope, ChatError, ChatStorage, Context, ConversationIdOwned, ConversationKind,
-    DeliveryService, InboundResult, Introduction, StorageConfig,
+    DeliveryService, Introduction, ProcessResponse, StorageConfig,
 };
 
 use components::EphemeralRegistry;
@@ -94,28 +94,48 @@ impl<D: DeliveryService + 'static> ChatClient<D> {
     }
 }
 
-/// Walk an [`InboundResult`] in causal order and emit one `Event` per
-/// observation. The structural ordering of `InboundResult` (new conversation
-/// before frame contents) determines the order of events here.
-fn events_from_inbound(result: InboundResult) -> Vec<Event> {
-    let mut events = Vec::with_capacity(
-        usize::from(result.new_conversation.is_some()) + result.frame.messages.len(),
-    );
-    if let Some(nc) = result.new_conversation
-        && let Some(class) = class_from_kind(&nc.kind)
-    {
+/// Walk a [`ProcessResponse`] in causal order and emit one `Event` per
+/// observation. New-conversation events are emitted before any frame
+/// contents from the same payload.
+fn events_from_inbound(result: ProcessResponse) -> Vec<Event> {
+    let mut events = Vec::new();
+    match result {
+        ProcessResponse::InboxResponse(r) => {
+            push_new_conversation(&mut events, r.new_conversation);
+            if let Some(frame) = r.frame {
+                push_frame(&mut events, frame);
+            }
+        }
+        ProcessResponse::ConvoResponse(r) => {
+            push_frame(&mut events, r.frame);
+        }
+        ProcessResponse::Unknown => {}
+    }
+    events
+}
+
+fn push_new_conversation(events: &mut Vec<Event>, nc: libchat::NewConversation) {
+    if let Some(class) = class_from_kind(&nc.kind) {
         events.push(Event::ConversationStarted {
             convo_id: nc.convo_id,
             class,
         });
     }
-    for msg in result.frame.messages {
+}
+
+fn push_frame(events: &mut Vec<Event>, frame: libchat::FrameOutcome) {
+    if let Some(msg) = frame.message {
         events.push(Event::MessageReceived {
             convo_id: msg.convo_id,
             content: msg.content,
         });
     }
-    events
+    for missing in frame.missing_messages {
+        events.push(Event::MessageMissing {
+            convo_id: std::sync::Arc::from(missing.conversation_id.as_str()),
+            message_id: missing.message_id,
+        });
+    }
 }
 
 /// Map a core [`ConversationKind`] to the coarse app-facing
diff --git a/crates/client/src/event.rs b/crates/client/src/event.rs
index 2353b3e..4139528 100644
--- a/crates/client/src/event.rs
+++ b/crates/client/src/event.rs
@@ -22,6 +22,12 @@ pub enum Event {
         convo_id: ConversationIdOwned,
         content: Vec<u8>,
     },
+    /// A causal-history gap surfaced: a message referenced by another
+    /// delivered message but never seen locally.
+    MessageMissing {
+        convo_id: ConversationIdOwned,
+        message_id: String,
+    },
 }
 
 /// Coarse classification of a conversation, intended as a UI/UX hint.