diff --git a/unshell-protocol/src/lib.rs b/unshell-protocol/src/lib.rs
index f8bfbd2..184bbad 100644
--- a/unshell-protocol/src/lib.rs
+++ b/unshell-protocol/src/lib.rs
@@ -34,6 +34,7 @@ type RouteMap = BTreeMap<EndpointName, PacketQueue>;
 
 #[cfg(test)]
 mod tests {
+    mod merkle_sync;
     mod oneshot;
     mod packet;
 }
diff --git a/unshell-protocol/src/tests/merkle_sync/codec.rs b/unshell-protocol/src/tests/merkle_sync/codec.rs
new file mode 100644
index 0000000..83c4047
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/codec.rs
@@ -0,0 +1,79 @@
+use alloc::vec::Vec;
+
+use super::tree::{BlockChunk, ChildKind, ChildSummary};
+
+/// Encodes one `u32` request or response payload.
+pub(super) fn encode_u32(value: u32) -> Vec<u8> {
+    value.to_le_bytes().to_vec()
+}
+
+/// Decodes one exact `u32` payload.
+pub(super) fn decode_u32(data: &[u8]) -> Option<u32> {
+    if data.len() == 4 {
+        Some(read_u32(data, 0))
+    } else {
+        None
+    }
+}
+
+/// Encodes one streamed child hash entry.
+pub(super) fn encode_child_summary(summary: ChildSummary) -> Vec<u8> {
+    let mut data = Vec::with_capacity(12);
+    data.extend_from_slice(&summary.id.to_le_bytes());
+    data.extend_from_slice(&summary.kind.discriminant().to_le_bytes());
+    data.extend_from_slice(&summary.hash.to_le_bytes());
+    data
+}
+
+/// Decodes one streamed child hash entry.
+pub(super) fn decode_child_summary(data: &[u8]) -> Option<ChildSummary> {
+    if data.len() != 12 {
+        return None;
+    }
+
+    Some(ChildSummary {
+        id: read_u32(data, 0),
+        kind: ChildKind::from_discriminant(read_u32(data, 4))?,
+        hash: read_u32(data, 8),
+    })
+}
+
+/// Encodes one streamed block chunk.
+pub(super) fn encode_block_chunk(chunk: &BlockChunk) -> Vec<u8> {
+    let mut data = Vec::with_capacity(16 + chunk.data.len());
+    data.extend_from_slice(&chunk.block_id.to_le_bytes());
+    data.extend_from_slice(&chunk.index.to_le_bytes());
+    data.extend_from_slice(&chunk.total.to_le_bytes());
+    data.extend_from_slice(&(chunk.data.len() as u32).to_le_bytes());
+    data.extend_from_slice(&chunk.data);
+    data
+}
+
+/// Decodes one streamed block chunk.
+pub(super) fn decode_block_chunk(data: &[u8]) -> Option<BlockChunk> {
+    if data.len() < 16 {
+        return None;
+    }
+
+    let len = read_u32(data, 12) as usize;
+    if data.len() != 16 + len {
+        return None;
+    }
+
+    Some(BlockChunk {
+        block_id: read_u32(data, 0),
+        index: read_u32(data, 4),
+        total: read_u32(data, 8),
+        data: data[16..].to_vec(),
+    })
+}
+
+/// Reads a little-endian `u32` at a known-valid offset.
+fn read_u32(data: &[u8], offset: usize) -> u32 {
+    u32::from_le_bytes([
+        data[offset],
+        data[offset + 1],
+        data[offset + 2],
+        data[offset + 3],
+    ])
+}
diff --git a/unshell-protocol/src/tests/merkle_sync/constants.rs b/unshell-protocol/src/tests/merkle_sync/constants.rs
new file mode 100644
index 0000000..72ccca7
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/constants.rs
@@ -0,0 +1,27 @@
+//! Shared ids for the Merkle sync protocol test.
+//!
+//! Keeping ids in one file makes the manually managed leaf state easier to audit
+//! and mirrors the table a future leaf-state macro would generate from annotated
+//! RPC definitions.
+
+pub(super) const ENDPOINT_CALLER: u32 = 0;
+pub(super) const ENDPOINT_RESPONDENT: u32 = 1;
+
+pub(super) const LEAF_MERKLE_CALLER: u32 = 300;
+pub(super) const LEAF_MERKLE_RESPONDENT: u32 = 301;
+pub(super) const LEAF_MOCK_CONNECTION: u32 = 302;
+
+pub(super) const PROC_GET_ROOT_HASH: u32 = 10;
+pub(super) const PROC_GET_CHILD_HASHES: u32 = 11;
+pub(super) const PROC_GET_BLOCK_STREAM: u32 = 12;
+pub(super) const PROC_ROOT_HASH: u32 = 20;
+pub(super) const PROC_CHILD_HASH_ENTRY: u32 = 21;
+pub(super) const PROC_BLOCK_CHUNK: u32 = 22;
+
+pub(super) const ROOT_NODE: u32 = 0;
+pub(super) const BRANCH_LEFT: u32 = 1;
+pub(super) const BRANCH_RIGHT: u32 = 2;
+pub(super) const BLOCK_ALPHA: u32 = 10;
+pub(super) const BLOCK_BRAVO: u32 = 11;
+pub(super) const BLOCK_CHARLIE: u32 = 20;
+pub(super) const BLOCK_DELTA: u32 = 21;
diff --git a/unshell-protocol/src/tests/merkle_sync/harness.rs b/unshell-protocol/src/tests/merkle_sync/harness.rs
new file mode 100644
index 0000000..34d544c
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/harness.rs
@@ -0,0 +1,119 @@
+use alloc::{boxed::Box, rc::Rc, vec};
+use core::cell::RefCell;
+
+use crate::Endpoint;
+
+use super::{
+    constants::{ENDPOINT_CALLER, ENDPOINT_RESPONDENT},
+    leaves::{MerkleCallerLeaf, MerkleRespondentLeaf, MockConnectionLeaf},
+    state::{CallerReport, RespondentReport},
+    tree::{MerkleStore, local_fixture, remote_fixture},
+};
+
+/// Complete two-endpoint Merkle sync test harness.
+///
+/// Endpoint A owns the caller leaf and one mock connection leaf. Endpoint B owns the
+/// respondent leaf and the opposite mock connection leaf. Reports are shared out of
+/// the boxed leaf objects so tests can assert state without downcasting trait
+/// objects.
+pub(super) struct MerkleHarness {
+    pub(super) endpoint_a: Endpoint,
+    pub(super) endpoint_b: Endpoint,
+    pub(super) caller_report: Rc<RefCell<CallerReport>>,
+    pub(super) respondent_report: Rc<RefCell<RespondentReport>>,
+    pub(super) remote_root_hash: u32,
+}
+
+impl MerkleHarness {
+    /// Creates the divergent fixture used by the main sync test.
+    pub(super) fn divergent() -> Self {
+        Self::with_stores(local_fixture(), remote_fixture())
+    }
+
+    /// Creates a custom caller/respondent fixture.
+    pub(super) fn with_stores(local: MerkleStore, remote: MerkleStore) -> Self {
+        let remote_root_hash = remote.root_hash();
+        let caller_report = Rc::new(RefCell::new(CallerReport::default()));
+        let respondent_report = Rc::new(RefCell::new(RespondentReport::default()));
+        let (tx_a, rx_a) = crossbeam_channel::unbounded();
+        let (tx_b, rx_b) = crossbeam_channel::unbounded();
+
+        let mut endpoint_a = Endpoint::new(
+            ENDPOINT_CALLER,
+            vec![
+                Box::new(MerkleCallerLeaf::new(local, caller_report.clone())),
+                Box::new(MockConnectionLeaf::new(
+                    tx_b,
+                    rx_a,
+                    ENDPOINT_RESPONDENT,
+                    false,
+                )),
+            ],
+        );
+        endpoint_a.path = vec![ENDPOINT_CALLER];
+
+        let mut endpoint_b = Endpoint::new(
+            ENDPOINT_RESPONDENT,
+            vec![
+                Box::new(MerkleRespondentLeaf::new(remote, respondent_report.clone())),
+                Box::new(MockConnectionLeaf::new(tx_a, rx_b, ENDPOINT_CALLER, true)),
+            ],
+        );
+        endpoint_b.path = vec![ENDPOINT_CALLER, ENDPOINT_RESPONDENT];
+
+        // Register routes before the first caller update so initial packet delivery
+        // does not depend on leaf ordering.
+        endpoint_a.connections.insert((ENDPOINT_RESPONDENT, false));
+        endpoint_b.connections.insert((ENDPOINT_CALLER, true));
+
+        Self {
+            endpoint_a,
+            endpoint_b,
+            caller_report,
+            respondent_report,
+            remote_root_hash,
+        }
+    }
+
+    /// Drives one deterministic protocol loop.
+    pub(super) fn tick(&mut self) {
+        self.endpoint_a.update();
+        self.endpoint_b.update();
+    }
+
+    /// Runs until the caller reports completion.
+    pub(super) fn run_until_done(&mut self, max_ticks: usize) -> usize {
+        for tick in 1..=max_ticks {
+            self.tick();
+
+            if self.caller_report.borrow().done {
+                return tick;
+            }
+        }
+
+        panic!("Merkle sync did not finish within {max_ticks} ticks");
+    }
+
+    /// Runs until the respondent has sent at least `target_frames` frames.
+    pub(super) fn run_until_respondent_frames(
+        &mut self,
+        target_frames: usize,
+        max_ticks: usize,
+    ) -> usize {
+        for tick in 1..=max_ticks {
+            self.tick();
+
+            if self.respondent_report.borrow().frames_sent >= target_frames {
+                return tick;
+            }
+        }
+
+        panic!("respondent did not send {target_frames} frames within {max_ticks} ticks");
+    }
+
+    /// Verifies the requested four-leaf topology.
+    pub(super) fn assert_four_leaf_topology(&self) {
+        assert_eq!(self.endpoint_a.leaves.len(), 2);
+        assert_eq!(self.endpoint_b.leaves.len(), 2);
+    }
+}
diff --git a/unshell-protocol/src/tests/merkle_sync/leaves.rs b/unshell-protocol/src/tests/merkle_sync/leaves.rs
new file mode 100644
index 0000000..0803972
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/leaves.rs
@@ -0,0 +1,404 @@
+use alloc::{collections::VecDeque, rc::Rc, vec, vec::Vec};
+use core::cell::RefCell;
+
+use crossbeam_channel::{Receiver, Sender};
+
+use crate::{Endpoint, Leaf, Packet};
+
+use super::{
+    codec::{decode_block_chunk, decode_child_summary, decode_u32},
+    constants::{
+        ENDPOINT_CALLER, ENDPOINT_RESPONDENT, LEAF_MERKLE_CALLER, LEAF_MERKLE_RESPONDENT,
+        LEAF_MOCK_CONNECTION, PROC_BLOCK_CHUNK, PROC_CHILD_HASH_ENTRY, PROC_GET_BLOCK_STREAM,
+        PROC_GET_CHILD_HASHES, PROC_GET_ROOT_HASH, PROC_ROOT_HASH, ROOT_NODE,
+    },
+    rpc::{
+        block_chunk_frame, block_stream_request, child_hash_frame, child_hashes_request,
+        root_hash_frame, root_hash_request,
+    },
+    state::{CallerPhase, CallerReport, RespondentReport, ResponseStream},
+    tree::{BlockChunk, ChildKind, MerkleStore},
+};
+
+/// Leaf that simulates a serialized transport connection with crossbeam channels.
+///
+/// This is intentionally tiny and reusable. Both endpoints in the Merkle test have
+/// exactly one of these leaves, giving the requested four-leaf topology: caller,
+/// respondent, and two mock connections.
+pub(super) struct MockConnectionLeaf {
+    pub(super) tx: Sender<Vec<u8>>,
+    pub(super) rx: Receiver<Vec<u8>>,
+    pub(super) remote_id: u32,
+    pub(super) is_authority: bool,
+    pub(super) started: bool,
+}
+
+/// Caller leaf that drives the Merkle synchronization algorithm.
+pub(super) struct MerkleCallerLeaf {
+    local: MerkleStore,
+    phase: CallerPhase,
+    pending_nodes: VecDeque<u32>,
+    pending_blocks: VecDeque<u32>,
+    report: Rc<RefCell<CallerReport>>,
+}
+
+/// Respondent leaf that serves Merkle hash and block streams.
+pub(super) struct MerkleRespondentLeaf {
+    remote: MerkleStore,
+    active_stream: Option<ResponseStream>,
+    report: Rc<RefCell<RespondentReport>>,
+}
+
+impl MockConnectionLeaf {
+    /// Creates one side of a mock connection.
+    pub(super) fn new(
+        tx: Sender<Vec<u8>>,
+        rx: Receiver<Vec<u8>>,
+        remote_id: u32,
+        is_authority: bool,
+    ) -> Self {
+        Self {
+            tx,
+            rx,
+            remote_id,
+            is_authority,
+            started: false,
+        }
+    }
+}
+
+impl MerkleCallerLeaf {
+    /// Creates a caller with a local store and externally visible report.
+    pub(super) fn new(local: MerkleStore, report: Rc<RefCell<CallerReport>>) -> Self {
+        Self {
+            local,
+            phase: CallerPhase::NeedRoot,
+            pending_nodes: VecDeque::new(),
+            pending_blocks: VecDeque::new(),
+            report,
+        }
+    }
+}
+
+impl MerkleRespondentLeaf {
+    /// Creates a respondent backed by the authoritative remote store.
+    pub(super) fn new(remote: MerkleStore, report: Rc<RefCell<RespondentReport>>) -> Self {
+        Self {
+            remote,
+            active_stream: None,
+            report,
+        }
+    }
+}
+
+impl Leaf for MockConnectionLeaf {
+    fn get_id(&self) -> u32 {
+        LEAF_MOCK_CONNECTION
+    }
+
+    fn update(&mut self, endpoint: &mut Endpoint) {
+        if !self.started {
+            endpoint
+                .connections
+                .insert((self.remote_id, self.is_authority));
+            self.started = true;
+        }
+
+        while !self.rx.is_empty() {
+            let data = self.rx.recv().unwrap();
+
+            // Mock transports move untrusted bytes. Malformed frames are dropped so
+            // the sync state machine is tested only after packet parsing succeeds.
+            if let Ok(packet) = Packet::deserialize(&data) {
+                let _ = endpoint.add_inbound(packet);
+            }
+        }
+
+        endpoint.take_outbound_clear(self.remote_id, |packet| {
+            let data = packet.serialize().unwrap();
+            let _ = self.tx.send(data);
+        });
+    }
+}
+
+impl Leaf for MerkleCallerLeaf {
+    fn get_id(&self) -> u32 {
+        LEAF_MERKLE_CALLER
+    }
+
+    fn update(&mut self, endpoint: &mut Endpoint) {
+        self.receive_responses(endpoint);
+        self.dispatch_next_request(endpoint);
+    }
+}
+
+impl Leaf for MerkleRespondentLeaf {
+    fn get_id(&self) -> u32 {
+        LEAF_MERKLE_RESPONDENT
+    }
+
+    fn update(&mut self, endpoint: &mut Endpoint) {
+        self.open_stream_from_request(endpoint);
+        self.send_one_response_frame(endpoint);
+    }
+}
+
+impl MerkleCallerLeaf {
+    /// Consumes all response packets currently delivered to endpoint A.
+    fn receive_responses(&mut self, endpoint: &mut Endpoint) {
+        endpoint.take_inbound_clear(ENDPOINT_CALLER, |packet| {
+            self.report
+                .borrow_mut()
+                .received_procedures
+                .push(packet.procedure_id);
+            self.handle_response_packet(packet);
+        });
+    }
+
+    /// Handles one response packet according to the current caller phase.
+    fn handle_response_packet(&mut self, packet: &Packet) {
+        match &mut self.phase {
+            CallerPhase::AwaitRoot { hook_id } => {
+                assert_eq!(packet.hook_id, *hook_id);
+                assert_eq!(packet.procedure_id, PROC_ROOT_HASH);
+                let remote_root = decode_u32(&packet.data).expect("root hash payload");
+
+                if packet.end_hook {
+                    self.finish_root_response(remote_root);
+                }
+            }
+            CallerPhase::AwaitChildren {
+                hook_id,
+                node_id: _,
+                entries,
+            } => {
+                assert_eq!(packet.hook_id, *hook_id);
+                assert_eq!(packet.procedure_id, PROC_CHILD_HASH_ENTRY);
+                entries.push(decode_child_summary(&packet.data).expect("child summary payload"));
+
+                if packet.end_hook {
+                    self.finish_child_response();
+                }
+            }
+            CallerPhase::AwaitBlock {
+                hook_id,
+                block_id: _,
+                chunks,
+            } => {
+                assert_eq!(packet.hook_id, *hook_id);
+                assert_eq!(packet.procedure_id, PROC_BLOCK_CHUNK);
+                chunks.push(decode_block_chunk(&packet.data).expect("block chunk payload"));
+
+                if packet.end_hook {
+                    self.finish_block_response();
+                }
+            }
+            CallerPhase::NeedRoot | CallerPhase::Ready | CallerPhase::Done => {
+                panic!("unexpected Merkle response in phase {:?}", self.phase);
+            }
+        }
+    }
+
+    /// Applies the completed root response and decides whether tree walking is needed.
+    fn finish_root_response(&mut self, remote_root: u32) {
+        if self.local.root_hash() == remote_root {
+            self.mark_done();
+        } else {
+            self.pending_nodes.push_back(ROOT_NODE);
+            self.phase = CallerPhase::Ready;
+        }
+    }
+
+    /// Applies a completed child-hash stream.
+    fn finish_child_response(&mut self) {
+        let CallerPhase::AwaitChildren {
+            hook_id: _,
+            node_id: _,
+            entries,
+        } = core::mem::replace(&mut self.phase, CallerPhase::Ready)
+        else {
+            unreachable!();
+        };
+
+        for entry in entries {
+            if self.local.hash_for(entry.kind, entry.id) == entry.hash {
+                continue;
+            }
+
+            match entry.kind {
+                ChildKind::Branch => self.pending_nodes.push_back(entry.id),
+                ChildKind::Block => self.pending_blocks.push_back(entry.id),
+            }
+        }
+    }
+
+    /// Applies a completed block stream to the local store.
+    fn finish_block_response(&mut self) {
+        let CallerPhase::AwaitBlock {
+            hook_id: _,
+            block_id,
+            mut chunks,
+        } = core::mem::replace(&mut self.phase, CallerPhase::Ready)
+        else {
+            unreachable!();
+        };
+
+        chunks.sort_by_key(|chunk| chunk.index);
+        assert_eq!(
+            chunks.len(),
+            chunks.first().map(|chunk| chunk.total).unwrap_or(0) as usize
+        );
+
+        let new_chunks: Vec<Vec<u8>> = chunks.into_iter().map(|chunk| chunk.data).collect();
+        self.local.replace_block(block_id, new_chunks.clone());
+
+        let mut report = self.report.borrow_mut();
+        report.synchronized_blocks.push(block_id);
+        report.applied_block_chunks.push((block_id, new_chunks));
+    }
+
+    /// Sends the next request if the caller is not waiting on a response stream.
+    fn dispatch_next_request(&mut self, endpoint: &mut Endpoint) {
+        match self.phase {
+            CallerPhase::NeedRoot => {
+                let hook_id = self.send_request(endpoint, PROC_GET_ROOT_HASH, Vec::new());
+                endpoint.add_outbound(root_hash_request(hook_id)).unwrap();
+                self.phase = CallerPhase::AwaitRoot { hook_id };
+            }
+            CallerPhase::Ready => {
+                if let Some(node_id) = self.pending_nodes.pop_front() {
+                    let hook_id = self.send_request(endpoint, PROC_GET_CHILD_HASHES, Vec::new());
+                    endpoint
+                        .add_outbound(child_hashes_request(hook_id, node_id))
+                        .unwrap();
+                    self.phase = CallerPhase::AwaitChildren {
+                        hook_id,
+                        node_id,
+                        entries: Vec::new(),
+                    };
+                } else if let Some(block_id) = self.pending_blocks.pop_front() {
+                    let hook_id = self.send_request(endpoint, PROC_GET_BLOCK_STREAM, Vec::new());
+                    endpoint
+                        .add_outbound(block_stream_request(hook_id, block_id))
+                        .unwrap();
+                    self.phase = CallerPhase::AwaitBlock {
+                        hook_id,
+                        block_id,
+                        chunks: Vec::new(),
+                    };
+                } else {
+                    self.mark_done();
+                }
+            }
+            CallerPhase::AwaitRoot { .. }
+            | CallerPhase::AwaitChildren { .. }
+            | CallerPhase::AwaitBlock { .. }
+            | CallerPhase::Done => {}
+        }
+    }
+
+    /// Reserves a hook id and records the logical RPC request.
+    fn send_request(&mut self, endpoint: &mut Endpoint, procedure_id: u32, _data: Vec<u8>) -> u16 {
+        let hook_id = endpoint.get_hook_id();
+        self.report
+            .borrow_mut()
+            .requested_procedures
+            .push(procedure_id);
+        hook_id
+    }
+
+    /// Marks the synchronization complete and records the final local root.
+    fn mark_done(&mut self) {
+        self.phase = CallerPhase::Done;
+        let mut report = self.report.borrow_mut();
+        report.done = true;
+        report.final_root_hash = Some(self.local.root_hash());
+    }
+}
+
+impl MerkleRespondentLeaf {
+    /// Opens one response stream from the first pending local request.
+    fn open_stream_from_request(&mut self, endpoint: &mut Endpoint) {
+        if self.active_stream.is_some() {
+            return;
+        }
+
+        let mut request = None;
+        endpoint.take_inbound_clear(ENDPOINT_RESPONDENT, |packet| {
+            if request.is_none() {
+                request = Some((packet.hook_id, packet.procedure_id, packet.data.clone()));
+            }
+        });
+
+        let Some((hook_id, procedure_id, data)) = request else {
+            return;
+        };
+
+        let frames = self.frames_for_request(procedure_id, &data);
+        endpoint.hooks.insert(hook_id, ENDPOINT_CALLER);
+
+        self.report.borrow_mut().requests_seen.push(procedure_id);
+        if !frames.is_empty() {
+            self.report.borrow_mut().streams_started += 1;
+            self.active_stream = Some(ResponseStream::new(hook_id, frames));
+        }
+    }
+
+    /// Builds response frames for one request procedure.
+    fn frames_for_request(&self, procedure_id: u32, data: &[u8]) -> Vec<super::rpc::OutgoingFrame> {
+        match procedure_id {
+            PROC_GET_ROOT_HASH => vec![root_hash_frame(self.remote.root_hash())],
+            PROC_GET_CHILD_HASHES => {
+                let node_id = decode_u32(data).expect("child hash request node id");
+                self.remote
+                    .child_summaries(node_id)
+                    .into_iter()
+                    .map(child_hash_frame)
+                    .collect()
+            }
+            PROC_GET_BLOCK_STREAM => {
+                let block_id = decode_u32(data).expect("block stream request block id");
+                let chunks = self.remote.block_chunks(block_id);
+                let total = chunks.len() as u32;
+                chunks
+                    .into_iter()
+                    .enumerate()
+                    .map(|(index, data)| {
+                        block_chunk_frame(BlockChunk {
+                            block_id,
+                            index: index as u32,
+                            total,
+                            data,
+                        })
+                    })
+                    .collect()
+            }
+            _ => Vec::new(),
+        }
+    }
+
+    /// Sends at most one response frame per update loop.
+    fn send_one_response_frame(&mut self, endpoint: &mut Endpoint) {
+        let Some(stream) = self.active_stream.as_mut() else {
+            return;
+        };
+
+        if stream.is_empty() {
+            self.active_stream = None;
+            return;
+        }
+
+        let packet = stream.next_packet().expect("active stream frame");
+        if endpoint.add_outbound(packet).is_err() {
+            return;
+        }
+
+        self.report.borrow_mut().frames_sent += 1;
+        stream.advance();
+
+        if stream.is_complete() {
+            self.report.borrow_mut().streams_completed += 1;
+            self.active_stream = None;
+        }
+    }
+}
diff --git a/unshell-protocol/src/tests/merkle_sync/mod.rs b/unshell-protocol/src/tests/merkle_sync/mod.rs
new file mode 100644
index 0000000..7098fdf
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/mod.rs
@@ -0,0 +1,8 @@
+mod codec;
+mod constants;
+mod harness;
+mod leaves;
+mod rpc;
+mod state;
+mod tests;
+mod tree;
diff --git a/unshell-protocol/src/tests/merkle_sync/rpc.rs b/unshell-protocol/src/tests/merkle_sync/rpc.rs
new file mode 100644
index 0000000..01440e0
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/rpc.rs
@@ -0,0 +1,86 @@
+use alloc::{vec, vec::Vec};
+
+use crate::Packet;
+
+use super::{
+    codec::{encode_block_chunk, encode_child_summary, encode_u32},
+    constants::{
+        ENDPOINT_CALLER, ENDPOINT_RESPONDENT, PROC_BLOCK_CHUNK, PROC_CHILD_HASH_ENTRY,
+        PROC_GET_BLOCK_STREAM, PROC_GET_CHILD_HASHES, PROC_GET_ROOT_HASH, PROC_ROOT_HASH,
+    },
+    tree::{BlockChunk, ChildSummary},
+};
+
+/// One outbound response frame before it is wrapped in endpoint routing fields.
+///
+/// A response stream owns a list of these frames and asks each frame to become a
+/// packet only when the loop is ready to send it. That keeps retry behavior simple:
+/// a failed send does not consume the frame.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) struct OutgoingFrame {
+    procedure_id: u32,
+    data: Vec<u8>,
+}
+
+impl OutgoingFrame {
+    /// Wraps the frame in an upward packet for `hook_id`.
+    pub(super) fn to_packet(&self, hook_id: u16, end_hook: bool) -> Packet {
+        Packet {
+            hook_id,
+            end_hook,
+            path: vec![ENDPOINT_CALLER],
+            procedure_id: self.procedure_id,
+            data: self.data.clone(),
+        }
+    }
+}
+
+/// Builds the initial root-hash request.
+pub(super) fn root_hash_request(hook_id: u16) -> Packet {
+    request_packet(PROC_GET_ROOT_HASH, hook_id, Vec::new())
+}
+
+/// Builds a request for one branch node's child hashes.
+pub(super) fn child_hashes_request(hook_id: u16, node_id: u32) -> Packet {
+    request_packet(PROC_GET_CHILD_HASHES, hook_id, encode_u32(node_id))
+}
+
+/// Builds a request for one mismatched block's data stream.
+pub(super) fn block_stream_request(hook_id: u16, block_id: u32) -> Packet {
+    request_packet(PROC_GET_BLOCK_STREAM, hook_id, encode_u32(block_id))
+}
+
+/// Builds a single root-hash response frame.
+pub(super) fn root_hash_frame(root_hash: u32) -> OutgoingFrame {
+    OutgoingFrame {
+        procedure_id: PROC_ROOT_HASH,
+        data: encode_u32(root_hash),
+    }
+}
+
+/// Builds one streamed child hash entry response frame.
+pub(super) fn child_hash_frame(summary: ChildSummary) -> OutgoingFrame {
+    OutgoingFrame {
+        procedure_id: PROC_CHILD_HASH_ENTRY,
+        data: encode_child_summary(summary),
+    }
+}
+
+/// Builds one streamed block chunk response frame.
+pub(super) fn block_chunk_frame(chunk: BlockChunk) -> OutgoingFrame {
+    OutgoingFrame {
+        procedure_id: PROC_BLOCK_CHUNK,
+        data: encode_block_chunk(&chunk),
+    }
+}
+
+/// Builds a downward request packet.
+fn request_packet(procedure_id: u32, hook_id: u16, data: Vec<u8>) -> Packet {
+    Packet {
+        hook_id,
+        end_hook: true,
+        path: vec![ENDPOINT_CALLER, ENDPOINT_RESPONDENT],
+        procedure_id,
+        data,
+    }
+}
diff --git a/unshell-protocol/src/tests/merkle_sync/state.rs b/unshell-protocol/src/tests/merkle_sync/state.rs
new file mode 100644
index 0000000..92a8cea
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/state.rs
@@ -0,0 +1,98 @@
+use alloc::vec::Vec;
+
+use super::{
+    rpc::OutgoingFrame,
+    tree::{BlockChunk, ChildSummary},
+};
+
+/// Caller-side synchronization phase.
+///
+/// This is the manual state machine a future macro should be able to derive from
+/// RPC declarations. Each awaiting state owns the partial stream it is collecting,
+/// making it clear which packets are legal at each step.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) enum CallerPhase {
+    NeedRoot,
+    AwaitRoot {
+        hook_id: u16,
+    },
+    Ready,
+    AwaitChildren {
+        hook_id: u16,
+        node_id: u32,
+        entries: Vec<ChildSummary>,
+    },
+    AwaitBlock {
+        hook_id: u16,
+        block_id: u32,
+        chunks: Vec<BlockChunk>,
+    },
+    Done,
+}
+
+/// Test-visible caller observations.
+///
+/// The leaf itself lives behind `Box<dyn Leaf>`, so the harness keeps a shared
+/// report handle for assertions without needing downcasts.
+#[derive(Debug, Default)]
+pub(super) struct CallerReport {
+    pub(super) done: bool,
+    pub(super) requested_procedures: Vec<u32>,
+    pub(super) received_procedures: Vec<u32>,
+    pub(super) synchronized_blocks: Vec<u32>,
+    pub(super) applied_block_chunks: Vec<(u32, Vec<Vec<u8>>)>,
+    pub(super) final_root_hash: Option<u32>,
+}
+
+/// Test-visible respondent observations.
+#[derive(Debug, Default)]
+pub(super) struct RespondentReport {
+    pub(super) requests_seen: Vec<u32>,
+    pub(super) streams_started: usize,
+    pub(super) streams_completed: usize,
+    pub(super) frames_sent: usize,
+}
+
+/// Respondent-owned response stream.
+///
+/// It stores encoded frames and exposes packet construction one frame at a time.
+/// Since `next_packet` does not advance, a failed route can be retried by calling it
+/// again on the next loop.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) struct ResponseStream {
+    hook_id: u16,
+    frames: Vec<OutgoingFrame>,
+    next_index: usize,
+}
+
+impl ResponseStream {
+    /// Creates a response stream for one request hook.
+    pub(super) fn new(hook_id: u16, frames: Vec<OutgoingFrame>) -> Self {
+        Self {
+            hook_id,
+            frames,
+            next_index: 0,
+        }
+    }
+
+    /// Builds the next packet without advancing the stream.
+    pub(super) fn next_packet(&self) -> Option<crate::Packet> {
+        let frame = self.frames.get(self.next_index)?;
+        Some(frame.to_packet(self.hook_id, self.next_index + 1 == self.frames.len()))
+    }
+
+    /// Marks the current frame as successfully sent.
+    pub(super) fn advance(&mut self) {
+        self.next_index += 1;
+    }
+
+    /// Returns true once every frame has been sent.
+    pub(super) fn is_complete(&self) -> bool {
+        self.next_index >= self.frames.len()
+    }
+
+    /// Returns true when the request generated no frames.
+    pub(super) fn is_empty(&self) -> bool {
+        self.frames.is_empty()
+    }
+}
diff --git a/unshell-protocol/src/tests/merkle_sync/tests.rs b/unshell-protocol/src/tests/merkle_sync/tests.rs
new file mode 100644
index 0000000..ecd97bb
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/tests.rs
@@ -0,0 +1,78 @@
+use super::{
+    constants::{
+        BLOCK_BRAVO, BLOCK_CHARLIE, PROC_GET_BLOCK_STREAM, PROC_GET_CHILD_HASHES,
+        PROC_GET_ROOT_HASH,
+    },
+    harness::MerkleHarness,
+    tree::remote_fixture,
+};
+
+#[test]
+fn merkle_sync_walks_hash_tree_and_streams_changed_blocks() {
+    let mut harness = MerkleHarness::divergent();
+    harness.assert_four_leaf_topology();
+
+    let ticks = harness.run_until_done(100);
+    assert!(
+        ticks > 20,
+        "sync should require many request/stream iterations"
+    );
+
+    let caller = harness.caller_report.borrow();
+    assert_eq!(caller.final_root_hash, Some(harness.remote_root_hash));
+    assert_eq!(caller.synchronized_blocks, [BLOCK_BRAVO, BLOCK_CHARLIE]);
+    assert_eq!(
+        caller.requested_procedures,
+        [
+            PROC_GET_ROOT_HASH,
+            PROC_GET_CHILD_HASHES,
+            PROC_GET_CHILD_HASHES,
+            PROC_GET_CHILD_HASHES,
+            PROC_GET_BLOCK_STREAM,
+            PROC_GET_BLOCK_STREAM,
+        ]
+    );
+
+    let respondent = harness.respondent_report.borrow();
+    assert_eq!(respondent.requests_seen, caller.requested_procedures);
+    assert_eq!(respondent.streams_started, 6);
+    assert_eq!(respondent.streams_completed, 6);
+    assert_eq!(respondent.frames_sent, 12);
+    assert!(harness.endpoint_b.hooks.is_empty());
+}
+
+#[test]
+fn identical_tree_stops_after_root_hash() {
+    let remote = remote_fixture();
+    let mut harness = MerkleHarness::with_stores(remote.clone(), remote);
+
+    harness.run_until_done(20);
+
+    let caller = harness.caller_report.borrow();
+    assert_eq!(caller.final_root_hash, Some(harness.remote_root_hash));
+    assert_eq!(caller.requested_procedures, [PROC_GET_ROOT_HASH]);
+    assert!(caller.synchronized_blocks.is_empty());
+
+    let respondent = harness.respondent_report.borrow();
+    assert_eq!(respondent.frames_sent, 1);
+    assert_eq!(respondent.streams_started, 1);
+    assert_eq!(respondent.streams_completed, 1);
+}
+
+#[test]
+fn block_stream_hook_persists_until_final_frame() {
+    let mut harness = MerkleHarness::divergent();
+
+    harness.run_until_respondent_frames(8, 100);
+    assert_eq!(
+        harness.endpoint_b.hooks.len(),
+        1,
+        "first block stream should keep its hook after a non-final chunk"
+    );
+
+    harness.run_until_done(100);
+    assert!(
+        harness.endpoint_b.hooks.is_empty(),
+        "final block stream packet should clean respondent hook state"
+    );
+}
diff --git a/unshell-protocol/src/tests/merkle_sync/tree.rs b/unshell-protocol/src/tests/merkle_sync/tree.rs
new file mode 100644
index 0000000..b0c8142
--- /dev/null
+++ b/unshell-protocol/src/tests/merkle_sync/tree.rs
@@ -0,0 +1,255 @@
+use alloc::{collections::BTreeMap, vec, vec::Vec};
+
+use super::constants::{
+    BLOCK_ALPHA, BLOCK_BRAVO, BLOCK_CHARLIE, BLOCK_DELTA, BRANCH_LEFT, BRANCH_RIGHT, ROOT_NODE,
+};
+
+/// Type of child referenced by a Merkle node summary.
+///
+/// The sync caller uses this to decide whether a mismatched child should recurse
+/// with `GET_CHILD_HASHES` or transfer data with `GET_BLOCK_STREAM`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(super) enum ChildKind {
+    Branch,
+    Block,
+}
+
+/// One child entry in a streamed Merkle summary response.
+///
+/// A respondent streams these one per loop. The caller compares each `hash` with
+/// its local store and queues either another node walk or a block transfer.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(super) struct ChildSummary {
+    pub(super) id: u32,
+    pub(super) kind: ChildKind,
+    pub(super) hash: u32,
+}
+
+/// One chunk in a streamed block response.
+///
+/// Chunks carry their total so the caller can replace the local block only after
+/// the final stream packet arrives. This keeps partially received data out of the
+/// Merkle hash until the hook completes.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) struct BlockChunk {
+    pub(super) block_id: u32,
+    pub(super) index: u32,
+    pub(super) total: u32,
+    pub(super) data: Vec<u8>,
+}
+
+/// Static edge in the test Merkle tree.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+struct TreeChild {
+    id: u32,
+    kind: ChildKind,
+}
+
+/// In-memory Merkle store used by the caller and respondent leaves.
+///
+/// This is deliberately small but extensible: adding wider trees, extra branches,
+/// or different block chunking only changes this store, not the endpoint routing
+/// harness. The hash is not cryptographic; it is deterministic test content used to
+/// exercise the protocol state machine.
+#[derive(Debug, Clone)]
+pub(super) struct MerkleStore {
+    root_id: u32,
+    children: BTreeMap<u32, Vec<TreeChild>>,
+    blocks: BTreeMap<u32, Vec<Vec<u8>>>,
+}
+
+impl MerkleStore {
+    /// Creates an empty store with the standard root id.
+    fn new() -> Self {
+        Self {
+            root_id: ROOT_NODE,
+            children: BTreeMap::new(),
+            blocks: BTreeMap::new(),
+        }
+    }
+
+    /// Returns the deterministic root hash for the current tree contents.
+    pub(super) fn root_hash(&self) -> u32 {
+        self.node_hash(self.root_id)
+    }
+
+    /// Returns child summaries for `node_id` in stable order.
+    pub(super) fn child_summaries(&self, node_id: u32) -> Vec<ChildSummary> {
+        self.children
+            .get(&node_id)
+            .map(|children| {
+                children
+                    .iter()
+                    .map(|child| ChildSummary {
+                        id: child.id,
+                        kind: child.kind,
+                        hash: self.hash_for(child.kind, child.id),
+                    })
+                    .collect()
+            })
+            .unwrap_or_default()
+    }
+
+    /// Returns the local hash for a branch or block child.
+    pub(super) fn hash_for(&self, kind: ChildKind, id: u32) -> u32 {
+        match kind {
+            ChildKind::Branch => self.node_hash(id),
+            ChildKind::Block => self.block_hash(id),
+        }
+    }
+
+    /// Returns the stored chunks for a block, preserving stream order.
+    pub(super) fn block_chunks(&self, block_id: u32) -> Vec<Vec<u8>> {
+        self.blocks.get(&block_id).cloned().unwrap_or_default()
+    }
+
+    /// Replaces one local block after a complete block stream arrives.
+    pub(super) fn replace_block(&mut self, block_id: u32, chunks: Vec<Vec<u8>>) {
+        self.blocks.insert(block_id, chunks);
+    }
+
+    /// Computes a deterministic hash for a branch node.
+    fn node_hash(&self, node_id: u32) -> u32 {
+        let mut hash = mix_u32(0x4E4F_4445, node_id);
+
+        if let Some(children) = self.children.get(&node_id) {
+            for child in children {
+                hash = mix_u32(hash, child.id);
+                hash = mix_u32(hash, child.kind.discriminant());
+                hash = mix_u32(hash, self.hash_for(child.kind, child.id));
+            }
+        }
+
+        hash
+    }
+
+    /// Computes a deterministic hash for a data block.
+    fn block_hash(&self, block_id: u32) -> u32 {
+        let mut hash = mix_u32(0x424C_4F43, block_id);
+
+        if let Some(chunks) = self.blocks.get(&block_id) {
+            for chunk in chunks {
+                hash = mix_u32(hash, chunk.len() as u32);
+                hash = hash_bytes(hash, chunk);
+            }
+        }
+
+        hash
+    }
+}
+
+impl ChildKind {
+    /// Stable wire discriminant for streamed child summaries.
+    pub(super) fn discriminant(self) -> u32 {
+        match self {
+            ChildKind::Branch => 0,
+            ChildKind::Block => 1,
+        }
+    }
+
+    /// Decodes a stable wire discriminant.
+    pub(super) fn from_discriminant(value: u32) -> Option<Self> {
+        match value {
+            0 => Some(Self::Branch),
+            1 => Some(Self::Block),
+            _ => None,
+        }
+    }
+}
+
+/// Remote store containing the authoritative content.
+pub(super) fn remote_fixture() -> MerkleStore {
+    let mut store = base_tree();
+    store
+        .blocks
+        .insert(BLOCK_ALPHA, chunks(&["alpha-", "same"]));
+    store
+        .blocks
+        .insert(BLOCK_BRAVO, chunks(&["bravo-", "remote-", "v2"]));
+    store
+        .blocks
+        .insert(BLOCK_CHARLIE, chunks(&["charlie-", "remote"]));
+    store.blocks.insert(BLOCK_DELTA, chunks(&["delta-same"]));
+    store
+}
+
+/// Local store with two stale blocks and two already matching blocks.
+pub(super) fn local_fixture() -> MerkleStore {
+    let mut store = base_tree();
+    store
+        .blocks
+        .insert(BLOCK_ALPHA, chunks(&["alpha-", "same"]));
+    store
+        .blocks
+        .insert(BLOCK_BRAVO, chunks(&["bravo-", "local-", "v1"]));
+    store
+        .blocks
+        .insert(BLOCK_CHARLIE, chunks(&["charlie-", "local"]));
+    store.blocks.insert(BLOCK_DELTA, chunks(&["delta-same"]));
+    store
+}
+
+/// Tree topology shared by the local and remote fixtures.
+fn base_tree() -> MerkleStore {
+    let mut store = MerkleStore::new();
+    store.children.insert(
+        ROOT_NODE,
+        vec![
+            TreeChild {
+                id: BRANCH_LEFT,
+                kind: ChildKind::Branch,
+            },
+            TreeChild {
+                id: BRANCH_RIGHT,
+                kind: ChildKind::Branch,
+            },
+        ],
+    );
+    store.children.insert(
+        BRANCH_LEFT,
+        vec![
+            TreeChild {
+                id: BLOCK_ALPHA,
+                kind: ChildKind::Block,
+            },
+            TreeChild {
+                id: BLOCK_BRAVO,
+                kind: ChildKind::Block,
+            },
+        ],
+    );
+    store.children.insert(
+        BRANCH_RIGHT,
+        vec![
+            TreeChild {
+                id: BLOCK_CHARLIE,
+                kind: ChildKind::Block,
+            },
+            TreeChild {
+                id: BLOCK_DELTA,
+                kind: ChildKind::Block,
+            },
+        ],
+    );
+    store
+}
+
+/// Converts string slices into owned byte chunks.
+fn chunks(parts: &[&str]) -> Vec<Vec<u8>> {
+    parts.iter().map(|part| part.as_bytes().to_vec()).collect()
+}
+
+/// FNV-like byte mixing used only for deterministic test hashes.
+fn hash_bytes(mut hash: u32, bytes: &[u8]) -> u32 {
+    for byte in bytes {
+        hash ^= u32::from(*byte);
+        hash = hash.wrapping_mul(16_777_619);
+    }
+
+    hash
+}
+
+/// Mixes one little-endian integer into the deterministic test hash.
+fn mix_u32(hash: u32, value: u32) -> u32 {
+    hash_bytes(hash, &value.to_le_bytes())
+}