diff --git a/Cargo.lock b/Cargo.lock
index f4743ec..e3d992c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3250,6 +3250,7 @@ dependencies = [
  "double-ratchets",
  "hashgraph-like-consensus",
  "hex",
+ "logos-account",
  "openmls",
  "openmls_libcrux_crypto 0.3.1",
  "openmls_memory_storage 0.5.0",
@@ -3590,8 +3591,9 @@ name = "logos-account"
 version = "0.1.0"
 dependencies = [
  "crypto",
- "libchat",
+ "hex",
  "shared-traits",
+ "thiserror",
 ]
 
 [[package]]
diff --git a/core/account/Cargo.toml b/core/account/Cargo.toml
index dbf71a9..c4d24c6 100644
--- a/core/account/Cargo.toml
+++ b/core/account/Cargo.toml
@@ -9,7 +9,8 @@ dev = []
 [dependencies]
 # Workspace dependencies (sorted)
 crypto = { workspace = true }
-libchat = { workspace = true }
 shared-traits = { workspace = true }
 
 # External dependencies (sorted)
+hex = "0.4.3"
+thiserror = "2.0.17"
diff --git a/core/account/src/account.rs b/core/account/src/account.rs
index db2959b..8e34fc5 100644
--- a/core/account/src/account.rs
+++ b/core/account/src/account.rs
@@ -1,7 +1,5 @@
 use crypto::{Ed25519SigningKey, Ed25519VerifyingKey};
-use shared_traits::{IdentId, IdentIdRef};
-
-use libchat::IdentityProvider;
+use shared_traits::{IdentId, IdentIdRef, IdentityProvider};
 
 /// A Test Focused LogosAccount using a pre-defined identifier.
 /// The test account is not persisted, and uses a single user provided id.
diff --git a/core/account/src/credential.rs b/core/account/src/credential.rs
new file mode 100644
index 0000000..395b655
--- /dev/null
+++ b/core/account/src/credential.rs
@@ -0,0 +1,242 @@
+//! Account ↔ LocalIdentity binding carried inside the MLS leaf credential.
+//!
+//! A group message in MLS is signed by a per-device key — the **LocalIdentity**
+//! (a device/installation). On its own that key says nothing about which
+//! **Account** the device belongs to, so multiple LocalIdentities of one Account
+//! cannot be collapsed back to that Account on the receiving side.
+//!
+//! This module binds the two together *inside the credential itself*, so a
+//! receiver resolves both without any network round-trip or trusted directory:
+//!
+//! - the MLS leaf's signature key is the LocalIdentity device key (MLS already
+//!   proves the sender holds its private half), and
+//! - the credential content carries the Account key plus the Account's signature
+//!   endorsing that exact device key.
+//!
+//! [`resolve_sender`] verifies the endorsement against the device key the leaf
+//! actually signs with, yielding a [`MessageSender`] the application can trust.
+//! This is the inverse of the account → device directory in `libchat`
+//! (`account_directory`): that resolves an Account *to* its devices for invites;
+//! this resolves a device *back to* its Account on receipt.
+
+use crypto::{Ed25519Signature, Ed25519VerifyingKey};
+use shared_traits::IdentId;
+use thiserror::Error;
+
+/// Current credential content version. Bump when [`encode_credential`] changes.
+pub const CREDENTIAL_VERSION: u8 = 1;
+
+/// Domain-separation tag prepended to the credential content and folded into the
+/// endorsement message. The account key may sign other things (e.g. the device
+/// bundle in `account_directory`), so binding to this exact purpose stops a
+/// signature obtained elsewhere from being replayed here. The trailing NUL keeps
+/// it from being a prefix of any other domain.
+pub const CREDENTIAL_DOMAIN: &[u8] = b"libchat:account-local-identity\0";
+
+/// The verified sender of a group message: which Account, and which device
+/// (LocalIdentity) of that Account it was sent from. Both are hex-encoded
+/// Ed25519 verifying keys.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct MessageSender {
+    /// The Account the sending device belongs to.
+    pub account: IdentId,
+    /// The specific LocalIdentity (device/installation) that sent the message.
+    pub local_identity: IdentId,
+}
+
+/// Failures decoding or verifying an account-bound credential.
+#[derive(Debug, Error)]
+pub enum CredentialError {
+    #[error("credential is missing the account-local-identity domain prefix")]
+    Domain,
+    #[error("credential shorter than its declared layout")]
+    Short,
+    #[error("unsupported credential version {0}")]
+    Version(u8),
+    #[error("credential carries a malformed account key")]
+    AccountKey,
+    #[error("account endorsement of the local identity failed verification")]
+    SignatureInvalid,
+}
+
+/// The bytes the Account signs to endorse `device` as one of its LocalIdentities.
+///
+/// `account` is folded in alongside the device key so the signature is bound to
+/// the specific (account, device) pair, not just the device key in isolation.
+fn endorsement_message(account: &Ed25519VerifyingKey, device: &Ed25519VerifyingKey) -> Vec<u8> {
+    let mut msg = Vec::with_capacity(CREDENTIAL_DOMAIN.len() + 32 + 32);
+    msg.extend_from_slice(CREDENTIAL_DOMAIN);
+    msg.extend_from_slice(account.as_ref());
+    msg.extend_from_slice(device.as_ref());
+    msg
+}
+
+/// Produce the Account's endorsement of `device`, using the Account's signing
+/// capability. `sign` is the account authority's signer (a local key on testnet,
+/// or an external wallet/enclave), so the closure is fallible.
+pub fn endorse_local_identity<E>(
+    account: &Ed25519VerifyingKey,
+    device: &Ed25519VerifyingKey,
+    sign: impl FnOnce(&[u8]) -> Result<Ed25519Signature, E>,
+) -> Result<Ed25519Signature, E> {
+    sign(&endorsement_message(account, device))
+}
+
+/// Encode the MLS credential content that binds a LocalIdentity to its Account.
+///
+/// The device key is *not* embedded: it is the leaf's signature key, supplied
+/// out-of-band by MLS on the receiving side and passed to [`resolve_sender`].
+///
+/// ```text
+/// domain      : CREDENTIAL_DOMAIN    (constant prefix, NUL-terminated)
+/// version     : u8        (1 byte)
+/// account_pub : [u8; 32]  (32 bytes)
+/// endorsement : [u8; 64]  (64 bytes) — account signature over endorsement_message
+/// ```
+pub fn encode_credential(account: &Ed25519VerifyingKey, endorsement: &Ed25519Signature) -> Vec<u8> {
+    let mut out = Vec::with_capacity(CREDENTIAL_DOMAIN.len() + 1 + 32 + 64);
+    out.extend_from_slice(CREDENTIAL_DOMAIN);
+    out.push(CREDENTIAL_VERSION);
+    out.extend_from_slice(account.as_ref());
+    out.extend_from_slice(endorsement.as_ref());
+    out
+}
+
+/// Decode `credential_content` and verify the Account's endorsement against
+/// `device_key` — the key the MLS leaf actually signs with. On success the
+/// caller learns both the LocalIdentity (`device_key`) and the Account that
+/// vouches for it.
+pub fn resolve_sender(
+    credential_content: &[u8],
+    device_key: &Ed25519VerifyingKey,
+) -> Result<MessageSender, CredentialError> {
+    const HEADER: usize = 1 + 32 + 64;
+    let rest = credential_content
+        .strip_prefix(CREDENTIAL_DOMAIN)
+        .ok_or(CredentialError::Domain)?;
+    if rest.len() < HEADER {
+        return Err(CredentialError::Short);
+    }
+    let version = rest[0];
+    if version != CREDENTIAL_VERSION {
+        return Err(CredentialError::Version(version));
+    }
+
+    let account_bytes: [u8; 32] = rest[1..33].try_into().expect("33 - 1 == 32");
+    let account =
+        Ed25519VerifyingKey::from_bytes(&account_bytes).map_err(|_| CredentialError::AccountKey)?;
+    let sig_bytes: [u8; 64] = rest[33..97].try_into().expect("97 - 33 == 64");
+    let endorsement = Ed25519Signature::from(sig_bytes);
+
+    // Verifying under the account key, over a message that includes the *leaf's*
+    // device key, is what binds this device to this account. A credential lifted
+    // from another sender won't verify against the device key MLS hands us here.
+    account
+        .verify(&endorsement_message(&account, device_key), &endorsement)
+        .map_err(|_| CredentialError::SignatureInvalid)?;
+
+    Ok(MessageSender {
+        account: IdentId::new(hex::encode(account.as_ref())),
+        local_identity: IdentId::new(hex::encode(device_key.as_ref())),
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crypto::Ed25519SigningKey;
+    use std::convert::Infallible;
+
+    /// Sign with the account key, resolve under the device key: both identities
+    /// come back, hex-encoded.
+    #[test]
+    fn resolves_well_formed_credential() {
+        let account_key = Ed25519SigningKey::generate();
+        let account_pub = account_key.verifying_key();
+        let device_key = Ed25519SigningKey::generate();
+        let device_pub = device_key.verifying_key();
+
+        let endorsement = endorse_local_identity::<Infallible>(&account_pub, &device_pub, |m| {
+            Ok(account_key.sign(m))
+        })
+        .unwrap();
+        let content = encode_credential(&account_pub, &endorsement);
+
+        let sender = resolve_sender(&content, &device_pub).unwrap();
+        assert_eq!(sender.account.as_str(), hex::encode(account_pub.as_ref()));
+        assert_eq!(
+            sender.local_identity.as_str(),
+            hex::encode(device_pub.as_ref())
+        );
+    }
+
+    /// On testnet the account key *is* the device key (one device == one
+    /// account); resolution then reports the same id for both.
+    #[test]
+    fn single_key_account_resolves_to_itself() {
+        let key = Ed25519SigningKey::generate();
+        let pubkey = key.verifying_key();
+
+        let endorsement =
+            endorse_local_identity::<Infallible>(&pubkey, &pubkey, |m| Ok(key.sign(m))).unwrap();
+        let content = encode_credential(&pubkey, &endorsement);
+
+        let sender = resolve_sender(&content, &pubkey).unwrap();
+        assert_eq!(sender.account, sender.local_identity);
+    }
+
+    /// An endorsement for device A, presented with device B's key (as MLS would
+    /// hand it over if B forged a leaf), fails: the signature covers A's key.
+    #[test]
+    fn rejects_endorsement_for_a_different_device() {
+        let account_key = Ed25519SigningKey::generate();
+        let account_pub = account_key.verifying_key();
+        let device_a = Ed25519SigningKey::generate().verifying_key();
+        let device_b = Ed25519SigningKey::generate().verifying_key();
+
+        let endorsement = endorse_local_identity::<Infallible>(&account_pub, &device_a, |m| {
+            Ok(account_key.sign(m))
+        })
+        .unwrap();
+        let content = encode_credential(&account_pub, &endorsement);
+
+        assert!(matches!(
+            resolve_sender(&content, &device_b),
+            Err(CredentialError::SignatureInvalid)
+        ));
+    }
+
+    #[test]
+    fn rejects_missing_domain_short_and_bad_version() {
+        let account_key = Ed25519SigningKey::generate();
+        let account_pub = account_key.verifying_key();
+        let device = Ed25519SigningKey::generate().verifying_key();
+        let endorsement =
+            endorse_local_identity::<Infallible>(
+                &account_pub,
+                &device,
+                |m| Ok(account_key.sign(m)),
+            )
+            .unwrap();
+        let content = encode_credential(&account_pub, &endorsement);
+
+        // Strip the domain prefix.
+        assert!(matches!(
+            resolve_sender(&content[CREDENTIAL_DOMAIN.len()..], &device),
+            Err(CredentialError::Domain)
+        ));
+        // Domain present but body truncated.
+        let short = &content[..CREDENTIAL_DOMAIN.len() + 4];
+        assert!(matches!(
+            resolve_sender(short, &device),
+            Err(CredentialError::Short)
+        ));
+        // Wrong version byte (first byte after the domain prefix).
+        let mut bad_version = content.clone();
+        bad_version[CREDENTIAL_DOMAIN.len()] = 99;
+        assert!(matches!(
+            resolve_sender(&bad_version, &device),
+            Err(CredentialError::Version(99))
+        ));
+    }
+}
diff --git a/core/account/src/lib.rs b/core/account/src/lib.rs
index c33c296..773fc83 100644
--- a/core/account/src/lib.rs
+++ b/core/account/src/lib.rs
@@ -1,3 +1,10 @@
+mod credential;
+
+pub use credential::{
+    CREDENTIAL_DOMAIN, CREDENTIAL_VERSION, CredentialError, MessageSender, encode_credential,
+    endorse_local_identity, resolve_sender,
+};
+
 #[cfg(feature = "dev")]
 mod account;
 
diff --git a/core/conversations/Cargo.toml b/core/conversations/Cargo.toml
index 52caa29..3ca2a1f 100644
--- a/core/conversations/Cargo.toml
+++ b/core/conversations/Cargo.toml
@@ -11,6 +11,7 @@ crate-type = ["rlib"]
 blake2 = { workspace = true }
 chat-sqlite = { workspace = true }
 crypto = { workspace = true }
+logos-account = { workspace = true }
 shared-traits = { workspace = true }
 storage = { workspace = true }
 
diff --git a/core/conversations/src/conversation/group_v1.rs b/core/conversations/src/conversation/group_v1.rs
index 0d0d433..49ad0d2 100644
--- a/core/conversations/src/conversation/group_v1.rs
+++ b/core/conversations/src/conversation/group_v1.rs
@@ -5,6 +5,8 @@
 use blake2::{Blake2b, Digest, digest::consts::U6};
 use chat_proto::logoschat::encryption::{EncryptedPayload, Plaintext, encrypted_payload};
 use chat_proto::logoschat::reliability::ReliablePayload;
+use crypto::Ed25519VerifyingKey;
+use logos_account::MessageSender;
 use openmls::prelude::tls_codec::Deserialize;
 use openmls::prelude::*;
 use prost::Message as _;
@@ -40,13 +42,9 @@ impl GroupV1Convo {
     // Create a new conversation with the creator as the only participant.
     pub fn new<S: ExternalServices>(cx: &mut ServiceContext<S>) -> Result<Self, ChatError> {
         let config = Self::mls_create_config(cx);
-        let mls_group = MlsGroup::new(
-            &cx.mls_provider,
-            &cx.mls_identity,
-            &config,
-            cx.mls_identity.get_credential(),
-        )
-        .unwrap();
+        let credential = cx.mls_identity.get_credential()?;
+        let mls_group =
+            MlsGroup::new(&cx.mls_provider, &cx.mls_identity, &config, credential).unwrap();
         let convo_id = hex::encode(mls_group.group_id().as_slice());
         Self::subscribe(&mut cx.ds, &convo_id)?;
 
@@ -178,6 +176,26 @@ impl GroupV1Convo {
         &self.convo_id
     }
 
+    /// Resolve the verified [`MessageSender`] for a processed message.
+    ///
+    /// MLS guarantees the message was signed by the sender leaf's key, which is
+    /// the device (LocalIdentity) key. We pair that authoritative key with the
+    /// account binding carried in the credential to recover both the Account and
+    /// the LocalIdentity. Returns `None` for non-member senders or if the
+    /// credential isn't a well-formed, validly-endorsed account binding.
+    fn resolve_sender(&self, processed: &ProcessedMessage) -> Option<MessageSender> {
+        let Sender::Member(leaf_index) = processed.sender() else {
+            return None;
+        };
+        // The leaf's signature key is the device key MLS verified the message
+        // against — the trustworthy LocalIdentity, not anything self-asserted in
+        // the credential content.
+        let member = self.mls_group.member_at(*leaf_index)?;
+        let key_bytes: [u8; 32] = member.signature_key.as_slice().try_into().ok()?;
+        let device_key = Ed25519VerifyingKey::from_bytes(&key_bytes).ok()?;
+        logos_account::resolve_sender(processed.credential().serialized_content(), &device_key).ok()
+    }
+
     fn send_message<S: ExternalServices>(
         &mut self,
         content: &[u8],
@@ -252,6 +270,10 @@ impl<S: ExternalServices> Convo<S> for GroupV1Convo {
             .process_message(&cx.mls_provider, protocol_message)
             .map_err(ChatError::generic)?;
 
+        // Resolve the sender before consuming `processed`; only surfaced
+        // alongside application content below.
+        let sender = self.resolve_sender(&processed);
+
         let content = match processed.into_content() {
             ProcessedMessageContent::ApplicationMessage(msg) => {
                 let reliable = ReliablePayload::decode(msg.into_bytes().as_slice())?;
@@ -271,9 +293,14 @@ impl<S: ExternalServices> Convo<S> for GroupV1Convo {
                 None
             }
         };
+        // A commit (content == None) has a sender but no application payload;
+        // keep the sender paired with content so consumers see it only on
+        // actual messages.
+        let sender = content.as_ref().and(sender);
         Ok(ConvoOutcome {
             convo_id: self.id().to_string(),
             content,
+            sender,
         })
     }
 
diff --git a/core/conversations/src/conversation/group_v2.rs b/core/conversations/src/conversation/group_v2.rs
index c8a42cb..aa0ff67 100644
--- a/core/conversations/src/conversation/group_v2.rs
+++ b/core/conversations/src/conversation/group_v2.rs
@@ -21,6 +21,7 @@ use de_mls::protos::de_mls::messages::v1::{
 };
 use de_mls::session::{Conversation, ConversationConfig, ConversationDeps};
 use hashgraph_like_consensus::signing::EthereumConsensusSigner;
+use logos_account::MessageSender;
 use prost::Message;
 use shared_traits::{IdentId, IdentIdRef};
 use std::sync::Arc;
@@ -460,6 +461,16 @@ impl GroupV2Convo {
                 content: Some(Content {
                     bytes: cm.message.clone(),
                 }),
+                // de-mls carries only the sender's member-id (the LocalIdentity
+                // display string); it does not yet expose an account-bound
+                // credential the way GroupV1 does. Surface the LocalIdentity and
+                // treat it as its own Account (the testnet 1:1 case).
+                // TODO: resolve the Account once de-mls exposes the sender
+                // credential, mirroring GroupV1Convo::resolve_sender.
+                sender: Some(MessageSender {
+                    account: IdentId::new(cm.sender.clone()),
+                    local_identity: IdentId::new(cm.sender.clone()),
+                }),
             }),
             _ => None,
         })
diff --git a/core/conversations/src/conversation/privatev1.rs b/core/conversations/src/conversation/privatev1.rs
index 8bb1a1e..80db85e 100644
--- a/core/conversations/src/conversation/privatev1.rs
+++ b/core/conversations/src/conversation/privatev1.rs
@@ -273,6 +273,8 @@ impl<S: ExternalServices> Convo<S> for PrivateV1Convo {
         Ok(ConvoOutcome {
             convo_id: self.id().to_string(),
             content,
+            // TODO: surface the peer identity for 1:1 conversations.
+            sender: None,
         })
     }
 
diff --git a/core/conversations/src/inbox_v2.rs b/core/conversations/src/inbox_v2.rs
index 23589ff..57d68c0 100644
--- a/core/conversations/src/inbox_v2.rs
+++ b/core/conversations/src/inbox_v2.rs
@@ -205,14 +205,10 @@ impl InboxV2 {
             .ciphersuites(vec![CIPHER_SUITE])
             .extensions(vec![ExtensionType::ApplicationId])
             .build();
+        let credential = cx.mls_identity.get_credential()?;
         let a = KeyPackage::builder()
             .leaf_node_capabilities(capabilities)
-            .build(
-                CIPHER_SUITE,
-                &cx.mls_provider,
-                &cx.mls_identity,
-                cx.mls_identity.get_credential(),
-            )
+            .build(CIPHER_SUITE, &cx.mls_provider, &cx.mls_identity, credential)
             .expect("Failed to build KeyPackage");
 
         Ok(a.key_package().clone())
diff --git a/core/conversations/src/inbox_v2/identity.rs b/core/conversations/src/inbox_v2/identity.rs
index 779f90b..4dfa854 100644
--- a/core/conversations/src/inbox_v2/identity.rs
+++ b/core/conversations/src/inbox_v2/identity.rs
@@ -9,6 +9,7 @@ use openmls_traits::{
 use shared_traits::IdentIdRef;
 
 use crate::AccountAuthority;
+use crate::ChatError;
 use crate::IdentityProvider;
 
 /// A Wrapper for an IdentityProvider which provides MLS specific functionality
@@ -23,11 +24,25 @@ impl<T: IdentityProvider> MlsIdentityProvider<T> {
         Self(inner)
     }
 
-    pub fn get_credential(&self) -> CredentialWithKey {
-        CredentialWithKey {
-            credential: BasicCredential::new(self.id().as_str().as_bytes().to_vec()).into(),
-            signature_key: self.public_key().as_ref().into(),
-        }
+    /// Build the MLS leaf credential for this identity.
+    ///
+    /// The credential content binds this device (LocalIdentity) to its Account:
+    /// the leaf's signature key is the device key, and the content carries the
+    /// Account key plus the Account's endorsement of that device key. A receiver
+    /// recovers both via [`logos_account::resolve_sender`]. On testnet the
+    /// account key *is* the device key, so the endorsement is self-signed.
+    pub fn get_credential(&self) -> Result<CredentialWithKey, ChatError> {
+        let account = AccountAuthority::account_pub(self).clone();
+        let device = self.public_key().clone();
+        let endorsement = logos_account::endorse_local_identity(&account, &device, |msg| {
+            AccountAuthority::sign(self, msg)
+        })
+        .map_err(|e| ChatError::Generic(e.to_string()))?;
+        let content = logos_account::encode_credential(&account, &endorsement);
+        Ok(CredentialWithKey {
+            credential: BasicCredential::new(content).into(),
+            signature_key: device.as_ref().into(),
+        })
     }
 }
 
diff --git a/core/conversations/src/lib.rs b/core/conversations/src/lib.rs
index b701b12..fa8ff09 100644
--- a/core/conversations/src/lib.rs
+++ b/core/conversations/src/lib.rs
@@ -23,6 +23,7 @@ pub use chat_sqlite::ChatStorage;
 pub use chat_sqlite::StorageConfig;
 pub use core::{ConversationId, Core, Introduction};
 pub use errors::ChatError;
+pub use logos_account::MessageSender;
 pub use outcomes::{
     Content, ConversationClass, ConvoOutcome, InboxOutcome, NewConversation, PayloadOutcome,
 };
diff --git a/core/conversations/src/outcomes.rs b/core/conversations/src/outcomes.rs
index 3209da8..1cb6545 100644
--- a/core/conversations/src/outcomes.rs
+++ b/core/conversations/src/outcomes.rs
@@ -6,6 +6,7 @@
 //!   initial [`ConvoOutcome`].
 //! - [`PayloadOutcome`] — the union of the above, plus `Empty`.
 
+use logos_account::MessageSender;
 use storage::ConversationKind;
 
 use crate::conversation::ConversationId;
@@ -19,6 +20,11 @@ pub struct Content {
 pub struct ConvoOutcome {
     pub convo_id: ConversationId,
     pub content: Option<Content>,
+    /// The verified sender of `content`: both the Account and the specific
+    /// LocalIdentity (device) it was sent from. `None` for control messages
+    /// (e.g. MLS commits) that carry no application content, and for
+    /// conversation types that don't yet surface a sender.
+    pub sender: Option<MessageSender>,
 }
 
 impl ConvoOutcome {
@@ -26,6 +32,7 @@ impl ConvoOutcome {
         Self {
             convo_id,
             content: None,
+            sender: None,
         }
     }
 }
diff --git a/core/integration_tests_core/src/test_client.rs b/core/integration_tests_core/src/test_client.rs
index 3843f93..47f6ab9 100644
--- a/core/integration_tests_core/src/test_client.rs
+++ b/core/integration_tests_core/src/test_client.rs
@@ -1,4 +1,4 @@
-use libchat::{ConversationId, Core, IdentityProvider, PayloadOutcome};
+use libchat::{ConversationId, Core, IdentityProvider, MessageSender, PayloadOutcome};
 use logos_account::TestLogosAccount;
 use shared_traits::IdentId;
 use std::collections::HashMap;
@@ -34,6 +34,8 @@ type ClientType = Core<(
 pub struct ReceivedMessage<T> {
     pub convo_id: ConversationId,
     pub contents: T,
+    /// The verified sender (Account + LocalIdentity) surfaced with the message.
+    pub sender: Option<MessageSender>,
 }
 
 pub struct TestClient {
@@ -76,6 +78,7 @@ impl TestClient {
                         self.received_messages.push(ReceivedMessage {
                             convo_id: convo_outcome.convo_id.clone(),
                             contents: data.bytes.clone(),
+                            sender: convo_outcome.sender.clone(),
                         });
                     }
                 }
@@ -102,6 +105,15 @@ impl TestClient {
         false
     }
 
+    /// The verified sender recorded for the (first) message matching
+    /// `convo_id`/`content`, if any was received.
+    pub fn sender_of(&self, convo_id: &str, content: &[u8]) -> Option<&MessageSender> {
+        self.received_messages
+            .iter()
+            .find(|m| m.convo_id == convo_id && m.contents == content)
+            .and_then(|m| m.sender.as_ref())
+    }
+
     pub fn convo_count(&self) -> usize {
         self.list_conversations().map_or(0, |v| v.len())
     }
diff --git a/core/integration_tests_core/tests/mls_integration.rs b/core/integration_tests_core/tests/mls_integration.rs
index d80e690..e017b9e 100644
--- a/core/integration_tests_core/tests/mls_integration.rs
+++ b/core/integration_tests_core/tests/mls_integration.rs
@@ -57,4 +57,30 @@ fn create_group() {
 
     assert!(!harness.pax().check(&convo_id, M_R1));
     assert!(!harness.pax().check(&convo_id, M_P1));
+
+    // Every delivered message carries a verified sender: both the Account and
+    // the LocalIdentity it was sent from. On testnet each identity is its own
+    // single-device account, so the two resolve to the same key.
+    let raya_sender = harness
+        .saro()
+        .sender_of(&convo_id, M_R1)
+        .expect("Saro should see who sent Raya's message")
+        .clone();
+    assert_eq!(
+        raya_sender.account, raya_sender.local_identity,
+        "single-key testnet account resolves Account == LocalIdentity"
+    );
+
+    let pax_sender = harness
+        .saro()
+        .sender_of(&convo_id, M_P1)
+        .expect("Saro should see who sent Pax's message")
+        .clone();
+
+    // Distinct identities resolve to distinct senders — the basis for telling
+    // group members apart and for collapsing an account's devices to one Account.
+    assert_ne!(
+        raya_sender.account, pax_sender.account,
+        "Raya and Pax must resolve to different accounts"
+    );
 }
diff --git a/crates/client/src/client.rs b/crates/client/src/client.rs
index 17b5439..08f7404 100644
--- a/crates/client/src/client.rs
+++ b/crates/client/src/client.rs
@@ -261,11 +261,16 @@ fn events_from_inbound(result: PayloadOutcome) -> Vec<Event> {
 }
 
 fn convo_events(outcome: ConvoOutcome) -> Vec<Event> {
-    let ConvoOutcome { convo_id, content } = outcome;
+    let ConvoOutcome {
+        convo_id,
+        content,
+        sender,
+    } = outcome;
     content
         .map(|c| Event::MessageReceived {
             convo_id: Arc::from(convo_id),
             content: c.bytes,
+            sender,
         })
         .into_iter()
         .collect()
@@ -282,10 +287,13 @@ fn inbox_events(outcome: InboxOutcome) -> Vec<Event> {
         convo_id: Arc::clone(&id),
         class: new_conversation.class,
     });
-    if let Some(c) = initial.and_then(|co| co.content) {
+    if let Some(co) = initial
+        && let Some(c) = co.content
+    {
         events.push(Event::MessageReceived {
             convo_id: Arc::clone(&id),
             content: c.bytes,
+            sender: co.sender,
         });
     }
     events
diff --git a/crates/client/src/event.rs b/crates/client/src/event.rs
index e704050..c16da30 100644
--- a/crates/client/src/event.rs
+++ b/crates/client/src/event.rs
@@ -8,7 +8,7 @@
 
 use std::sync::Arc;
 
-use libchat::ConversationClass;
+use libchat::{ConversationClass, MessageSender};
 
 /// A discrete chat event.
 #[non_exhaustive]
@@ -23,6 +23,10 @@ pub enum Event {
     MessageReceived {
         convo_id: Arc<str>,
         content: Vec<u8>,
+        /// The verified sender — both the Account and the LocalIdentity
+        /// (device) it was sent from. `None` when the conversation type does
+        /// not yet surface a sender.
+        sender: Option<MessageSender>,
     },
     InboundError {
         message: String,
diff --git a/crates/client/tests/saro_and_raya.rs b/crates/client/tests/saro_and_raya.rs
index b588240..2299cef 100644
--- a/crates/client/tests/saro_and_raya.rs
+++ b/crates/client/tests/saro_and_raya.rs
@@ -37,7 +37,9 @@ fn saro_raya_message_exchange() {
         other => Err(other),
     });
     expect_event(&raya_events, "MessageReceived", |e| match e {
-        Event::MessageReceived { convo_id, content } => {
+        Event::MessageReceived {
+            convo_id, content, ..
+        } => {
             assert_eq!(convo_id, raya_convo_id);
             assert_eq!(content.as_slice(), b"hello raya");
             Ok(())