Merge pull request #542 from logos-blockchain/moudy/feat-cross-zone-messaging

feat!(cross-zone): async LEZ to LEZ cross-zone messaging

Cargo.lock

@@ -1154,6 +1154,25 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "bridge_lock_core"
+version = "0.1.0"
+dependencies = [
+ "lee_core",
+ "serde",
+]
+
+[[package]]
+name = "bridge_lock_program"
+version = "0.1.0"
+dependencies = [
+ "bridge_lock_core",
+ "cross_zone_outbox_core",
+ "lee_core",
+ "risc0-zkvm",
+ "wrapped_token_core",
+]
+
 [[package]]
 name = "bridge_program"
 version = "0.1.0"
@@ -1833,6 +1852,76 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "790eea4361631c5e7d22598ecd5723ff611904e3344ce8720784c93e3d83d40b"
 
+[[package]]
+name = "cross_zone"
+version = "0.1.0"
+dependencies = [
+ "bridge_lock_core",
+ "cross_zone_inbox_core",
+ "lee",
+ "lee_core",
+ "ping_core",
+ "programs",
+ "risc0-zkvm",
+]
+
+[[package]]
+name = "cross_zone_chat"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "axum 0.8.9",
+ "common",
+ "cross_zone_inbox_core",
+ "cross_zone_outbox_core",
+ "env_logger",
+ "lee",
+ "log",
+ "ping_core",
+ "programs",
+ "risc0-zkvm",
+ "sequencer_service_rpc",
+ "serde",
+ "test_fixtures",
+ "tokio",
+]
+
+[[package]]
+name = "cross_zone_inbox_core"
+version = "0.1.0"
+dependencies = [
+ "borsh",
+ "lee_core",
+ "risc0-zkvm",
+ "serde",
+]
+
+[[package]]
+name = "cross_zone_inbox_program"
+version = "0.1.0"
+dependencies = [
+ "cross_zone_inbox_core",
+ "lee_core",
+]
+
+[[package]]
+name = "cross_zone_outbox_core"
+version = "0.1.0"
+dependencies = [
+ "borsh",
+ "lee_core",
+ "risc0-zkvm",
+ "serde",
+]
+
+[[package]]
+name = "cross_zone_outbox_program"
+version = "0.1.0"
+dependencies = [
+ "cross_zone_outbox_core",
+ "lee_core",
+]
+
 [[package]]
 name = "crossbeam-channel"
 version = "0.5.15"
@@ -3851,13 +3940,19 @@ dependencies = [
  "async-stream",
  "borsh",
  "common",
+ "cross_zone",
+ "cross_zone_inbox_core",
  "futures",
+ "hex",
  "humantime-serde",
  "lee",
  "lee_core",
  "log",
  "logos-blockchain-core",
  "logos-blockchain-zone-sdk",
+ "ping_core",
+ "programs",
+ "risc0-zkvm",
  "serde",
  "serde_json",
  "storage",
@@ -4012,8 +4107,11 @@ dependencies = [
  "authenticated_transfer_core",
  "borsh",
  "bridge_core",
+ "bridge_lock_core",
  "bytesize",
  "common",
+ "cross_zone_inbox_core",
+ "cross_zone_outbox_core",
  "faucet_core",
  "futures",
  "hex",
@@ -4029,8 +4127,10 @@ dependencies = [
  "logos-blockchain-key-management-system-service",
  "logos-blockchain-zone-sdk",
  "num-bigint 0.4.6",
+ "ping_core",
  "programs",
  "reqwest",
+ "risc0-zkvm",
  "sequencer_core",
  "sequencer_service_rpc",
  "serde_json",
@@ -4043,6 +4143,7 @@ dependencies = [
  "vault_core",
  "wallet",
  "wallet-ffi",
+ "wrapped_token_core",
 ]
 
 [[package]]
@@ -7175,6 +7276,31 @@ dependencies = [
  "token_core",
 ]
 
+[[package]]
+name = "ping_core"
+version = "0.1.0"
+dependencies = [
+ "lee_core",
+ "serde",
+]
+
+[[package]]
+name = "ping_receiver_program"
+version = "0.1.0"
+dependencies = [
+ "lee_core",
+ "ping_core",
+]
+
+[[package]]
+name = "ping_sender_program"
+version = "0.1.0"
+dependencies = [
+ "cross_zone_outbox_core",
+ "lee_core",
+ "ping_core",
+]
+
 [[package]]
 name = "pkcs1"
 version = "0.7.5"
@@ -7447,15 +7573,20 @@ dependencies = [
  "associated_token_account_program",
  "authenticated_transfer_core",
  "bridge_core",
+ "bridge_lock_core",
  "build_utils",
  "clock_core",
+ "cross_zone_inbox_core",
+ "cross_zone_outbox_core",
  "faucet_core",
  "lee",
  "lee_core",
+ "ping_core",
  "risc0-zkvm",
  "token_core",
  "token_program",
  "vault_core",
+ "wrapped_token_core",
 ]
 
 [[package]]
@@ -8894,6 +9025,8 @@ dependencies = [
  "bytesize",
  "chrono",
  "common",
+ "cross_zone",
+ "cross_zone_inbox_core",
  "faucet_core",
  "futures",
  "hex",
@@ -9843,6 +9976,7 @@ dependencies = [
  "programs",
  "serde",
  "system_accounts",
+ "wrapped_token_core",
 ]
 
 [[package]]
@@ -11552,6 +11686,23 @@ dependencies = [
  "wasmparser",
 ]
 
+[[package]]
+name = "wrapped_token_core"
+version = "0.1.0"
+dependencies = [
+ "lee_core",
+ "risc0-zkvm",
+ "serde",
+]
+
+[[package]]
+name = "wrapped_token_program"
+version = "0.1.0"
+dependencies = [
+ "lee_core",
+ "wrapped_token_core",
+]
+
 [[package]]
 name = "writeable"
 version = "0.6.3"

Cargo.toml

@@ -43,6 +43,13 @@ members = [
   "lez/programs/pinata_token",
   "lez/programs/token",
   "lez/programs/vault",
+  "lez/programs/cross_zone_inbox",
+  "lez/programs/cross_zone_outbox",
+  "lez/programs/bridge_lock",
+  "lez/programs/wrapped_token",
+  "lez/programs/ping_sender",
+  "lez/programs/ping_receiver",
+  "lez/cross_zone",
 
   "test_programs",
   "test_programs/guest",
@@ -58,6 +65,7 @@ members = [
   "tools/cycle_bench",
   "tools/crypto_primitives_bench",
   "tools/integration_bench",
+  "tools/cross_zone_chat",
 ]
 
 [workspace.dependencies]
@@ -94,6 +102,12 @@ authenticated_transfer_core = { path = "lez/programs/authenticated_transfer/core
 faucet_core = { path = "lez/programs/faucet/core" }
 bridge_core = { path = "lez/programs/bridge/core" }
 vault_core = { path = "lez/programs/vault/core" }
+cross_zone_inbox_core = { path = "lez/programs/cross_zone_inbox/core" }
+cross_zone_outbox_core = { path = "lez/programs/cross_zone_outbox/core" }
+bridge_lock_core = { path = "lez/programs/bridge_lock/core" }
+wrapped_token_core = { path = "lez/programs/wrapped_token/core" }
+ping_core = { path = "lez/programs/ping_core" }
+cross_zone = { path = "lez/cross_zone" }
 build_utils = { path = "build_utils" }
 test_programs = { path = "test_programs" }
 testnet_initial_state = { path = "lez/testnet_initial_state" }
@@ -182,6 +196,7 @@ elliptic-curve = { version = "0.13.8", features = ["arithmetic"] }
 actix-web = { version = "4.13.0", default-features = false, features = [
   "macros",
 ] }
+axum = "0.8.4"
 clap = { version = "4.5.42", features = ["derive", "env"] }
 reqwest = { version = "0.12", features = ["json", "rustls-tls", "stream"] }
 pyo3 = { version = "0.29", features = ["auto-initialize"] }

Justfile

@@ -6,6 +6,11 @@ default:
 # ---- Configuration ----
 ARTIFACTS := "artifacts"
 
+# On macOS the integration-test binary links pyo3 against the CommandLineTools
+# Python framework with no embedded rpath, so it needs this to launch. Empty on
+# Linux/CI, which is unaffected.
+DEMO_ENV := if os() == "macos" { "DYLD_FALLBACK_FRAMEWORK_PATH=/Library/Developer/CommandLineTools/Library/Frameworks" } else { "" }
+
 # Build risc0 program artifacts.
 build-artifacts:
     @echo "🔨 Building artifacts"
@@ -99,6 +104,26 @@ wallet-import-test-accounts:
 
     just run-wallet account list
 
+# Demo: cross-zone ping. Boots two zones on one Bedrock and sends a message from
+# zone A to zone B, where the indexer re-derives and verifies it (Option B)
+# before ping_receiver records it. Dev mode, no proving.
+demo-cross-zone-ping:
+    @echo "📡 Cross-zone ping demo (message A → B, indexer-verified)"
+    {{DEMO_ENV}} RISC0_DEV_MODE=1 cargo test -p integration_tests --release --test cross_zone_verified -- --nocapture
+
+# Demo: cross-zone wrapped-token bridge. Locks a balance on zone A and mints the
+# wrapped token to a recipient on zone B over the same verified spine.
+demo-cross-zone-bridge:
+    @echo "🌉 Cross-zone bridge demo (lock on A, mint on B)"
+    {{DEMO_ENV}} RISC0_DEV_MODE=1 cargo test -p integration_tests --release --test cross_zone_bridge -- --nocapture
+
+# Demo: interactive cross-zone chat. Boots two zones on one Bedrock and serves a
+# local two-column web UI; type in one zone and watch the message cross into the
+# other. Two people can chat across the zones. Dev mode, no proving.
+cross-zone-chat:
+    @echo "💬 Cross-zone chat demo — open the printed localhost URL"
+    {{DEMO_ENV}} RISC0_DEV_MODE=1 cargo run -p cross_zone_chat --release
+
 # Clean runtime data
 clean:
     @echo "🧹 Cleaning run artifacts"

integration_tests/Cargo.toml

@@ -22,6 +22,12 @@ associated_token_account_core.workspace = true
 vault_core.workspace = true
 faucet_core.workspace = true
 bridge_core.workspace = true
+ping_core.workspace = true
+cross_zone_outbox_core.workspace = true
+cross_zone_inbox_core.workspace = true
+bridge_lock_core.workspace = true
+wrapped_token_core.workspace = true
+risc0-zkvm.workspace = true
 indexer_service_rpc = { workspace = true, features = ["client"] }
 sequencer_service_rpc = { workspace = true, features = ["client"] }
 wallet-ffi.workspace = true

integration_tests/tests/cross_zone_bridge.rs

@@ -0,0 +1,197 @@
+#![expect(
+    clippy::tests_outside_test_module,
+    reason = "top-level test functions are conventional for integration tests"
+)]
+
+//! Demo 2: a wrapped-token bridge over the cross-zone spine. A holder locks part
+//! of their bridgeable balance on zone A; the watcher carries the emitted mint to
+//! zone B, where the indexer re-derives and verifies it (Option B) before the
+//! wrapped token is minted to the recipient. Reuses the M3/M4 spine unchanged;
+//! only the source caller (`bridge_lock`) and target (`wrapped_token`) are new.
+
+use std::{net::SocketAddr, time::Duration};
+
+use anyhow::{Context as _, Result};
+use common::transaction::LeeTransaction;
+use cross_zone_outbox_core::outbox_pda;
+use integration_tests::{
+    config::{self, SequencerPartialConfig},
+    indexer_client::IndexerClient,
+    setup::{setup_bedrock_node, setup_indexer, setup_sequencer},
+};
+use lee::{
+    AccountId, PrivateKey, PublicKey, PublicTransaction,
+    public_transaction::{Message, WitnessSet},
+};
+use sequencer_core::config::{CrossZoneConfig, CrossZonePeer, GenesisAction};
+use sequencer_service_rpc::{RpcClient as _, SequencerClient, SequencerClientBuilder};
+use tokio::test;
+
+const DELIVERY_TIMEOUT: Duration = Duration::from_secs(600);
+const INITIAL_BALANCE: u128 = 100;
+const LOCK_AMOUNT: u128 = 30;
+const RECIPIENT: [u8; 32] = [9; 32];
+
+#[test]
+async fn lock_on_zone_a_mints_wrapped_token_on_zone_b() -> Result<()> {
+    // Declared first so it outlives both zones (drops run in reverse order).
+    let (_bedrock, bedrock_addr) = setup_bedrock_node()
+        .await
+        .context("Failed to set up shared Bedrock node")?;
+
+    let partial = SequencerPartialConfig::default();
+    let channel_a = config::bedrock_channel_id();
+    let channel_b = config::bedrock_channel_id_b();
+    let zone_b: [u8; 32] = *channel_b.as_ref();
+
+    let holder_key = PrivateKey::try_new([7; 32]).expect("valid key");
+    let holder_id = AccountId::from(&PublicKey::new_from_private_key(&holder_key));
+
+    let wrapped_token_id = programs::wrapped_token().id();
+    let cross_zone = CrossZoneConfig {
+        peers: vec![CrossZonePeer {
+            channel_id: *channel_a.as_ref(),
+            allowed_targets: vec![wrapped_token_id],
+            expected_block_signing_pubkey: None,
+        }],
+    };
+
+    // Zone A seeds the holder's bridgeable balance. Zone B runs the watcher on its
+    // sequencer and the verifier on its indexer.
+    let genesis_a = vec![GenesisAction::SupplyBridgeLockHolding {
+        holder: holder_id,
+        amount: INITIAL_BALANCE,
+    }];
+    let (seq_a, _seq_a_home) = setup_sequencer(partial, bedrock_addr, genesis_a, channel_a, None)
+        .await
+        .context("Failed to set up zone A sequencer")?;
+    let (_seq_b, _seq_b_home) = setup_sequencer(
+        partial,
+        bedrock_addr,
+        vec![],
+        channel_b,
+        Some(cross_zone.clone()),
+    )
+    .await
+    .context("Failed to set up zone B sequencer")?;
+    let (idx_b, _idx_b_home) = setup_indexer(bedrock_addr, channel_b, Some(cross_zone))
+        .await
+        .context("Failed to set up zone B indexer")?;
+
+    // Lock LOCK_AMOUNT on zone A, addressed to the recipient on zone B.
+    let lock = build_lock_tx(&holder_key, holder_id, zone_b);
+    sequencer_client(seq_a.addr())?
+        .send_transaction(lock)
+        .await
+        .context("Failed to submit lock on zone A")?;
+
+    // Wait until zone B's indexer reflects the verified mint.
+    let holding_id = wrapped_token_core::holding_account_id(wrapped_token_id, &RECIPIENT);
+    let indexer_url = config::addr_to_url(config::UrlProtocol::Ws, idx_b.addr())
+        .context("Failed to build indexer URL")?;
+    let indexer = IndexerClient::new(&indexer_url)
+        .await
+        .context("Failed to build indexer client")?;
+
+    let minted = wait_for_mint(&indexer, holding_id).await?;
+    assert_eq!(
+        minted, LOCK_AMOUNT,
+        "zone B must mint exactly the locked amount"
+    );
+
+    // Conservation: the mint on B must be backed by an equal lock on A. The lock
+    // has already landed (it preceded delivery), so zone A reflects the debit and
+    // escrow now.
+    let seq_a_client = sequencer_client(seq_a.addr())?;
+    let escrow_id = bridge_lock_core::escrow_account_id(programs::bridge_lock().id());
+    let escrowed = bridge_lock_core::read_balance(
+        &seq_a_client.get_account(escrow_id).await?.data.into_inner(),
+    );
+    assert_eq!(
+        escrowed, LOCK_AMOUNT,
+        "zone A escrow must hold the locked amount"
+    );
+    let remaining = bridge_lock_core::read_balance(
+        &seq_a_client.get_account(holder_id).await?.data.into_inner(),
+    );
+    assert_eq!(
+        remaining,
+        INITIAL_BALANCE - LOCK_AMOUNT,
+        "zone A holder must be debited by the locked amount"
+    );
+    Ok(())
+}
+
+/// Builds a signed `bridge_lock` Lock that forwards a wrapped-token Mint of the
+/// locked amount to the recipient on the target zone.
+fn build_lock_tx(
+    holder_key: &PrivateKey,
+    holder_id: AccountId,
+    target_zone: [u8; 32],
+) -> LeeTransaction {
+    let bridge_lock_id = programs::bridge_lock().id();
+    let wrapped_token_id = programs::wrapped_token().id();
+    let outbox_id = programs::cross_zone_outbox().id();
+    let ordinal = 0;
+
+    let mint = wrapped_token_core::Instruction::Mint {
+        recipient: RECIPIENT,
+        amount: LOCK_AMOUNT,
+    };
+    let words = risc0_zkvm::serde::to_vec(&mint).expect("serialize mint");
+    let payload: Vec<u8> = words.iter().flat_map(|word| word.to_le_bytes()).collect();
+
+    let target_accounts = vec![
+        wrapped_token_core::config_account_id(wrapped_token_id).into_value(),
+        wrapped_token_core::holding_account_id(wrapped_token_id, &RECIPIENT).into_value(),
+    ];
+    let lock = bridge_lock_core::Instruction::Lock {
+        amount: LOCK_AMOUNT,
+        target_zone,
+        target_program_id: wrapped_token_id,
+        target_accounts,
+        payload,
+        outbox_program_id: outbox_id,
+        ordinal,
+    };
+
+    let accounts = vec![
+        holder_id,
+        bridge_lock_core::escrow_account_id(bridge_lock_id),
+        outbox_pda(outbox_id, &target_zone, ordinal),
+    ];
+    // One nonce per signature: the holder signs, at its genesis nonce 0.
+    let message = Message::try_new(bridge_lock_id, accounts, vec![0_u128.into()], lock)
+        .expect("build lock message");
+    let witness = WitnessSet::for_message(&message, &[holder_key]);
+    LeeTransaction::Public(PublicTransaction::new(message, witness))
+}
+
+fn sequencer_client(addr: SocketAddr) -> Result<SequencerClient> {
+    let url = config::addr_to_url(config::UrlProtocol::Http, addr)
+        .context("Failed to build sequencer URL")?;
+    SequencerClientBuilder::default()
+        .build(url)
+        .context("Failed to build sequencer client")
+}
+
+/// Polls zone B's indexer until the recipient's wrapped holding is non-zero.
+async fn wait_for_mint(indexer: &IndexerClient, holding_id: AccountId) -> Result<u128> {
+    let account_id = indexer_service_protocol::AccountId {
+        value: holding_id.into_value(),
+    };
+    let wait = async {
+        loop {
+            let account =
+                indexer_service_rpc::RpcClient::get_account(&**indexer, account_id).await?;
+            let balance = wrapped_token_core::read_balance(&account.data.0);
+            if balance != 0 {
+                return Ok::<u128, anyhow::Error>(balance);
+            }
+            tokio::time::sleep(Duration::from_secs(3)).await;
+        }
+    };
+    tokio::time::timeout(DELIVERY_TIMEOUT, wait)
+        .await
+        .context("Zone B's indexer did not mint the wrapped token in time")?
+}

integration_tests/tests/cross_zone_ingress_guard.rs

@@ -0,0 +1,80 @@
+#![expect(
+    clippy::tests_outside_test_module,
+    reason = "We don't care about these in tests"
+)]
+
+//! M6 ingress guard: the cross-zone inbox is sequencer-only. Only the watcher
+//! injects inbox dispatches; a user must not be able to invoke the inbox through
+//! the public RPC, or anyone could forge an inbound cross-zone delivery. The
+//! inbox guest's caller-is-none assertion passes for a top-level user tx, so the
+//! sequencer ingress guard is the only thing that stops this.
+
+use std::net::SocketAddr;
+
+use anyhow::{Context as _, Result};
+use common::transaction::LeeTransaction;
+use cross_zone_inbox_core::{
+    CrossZoneMessage, Instruction, inbox_config_account_id, inbox_seen_shard_account_id,
+};
+use integration_tests::{
+    config::{self, SequencerPartialConfig},
+    setup::{setup_bedrock_node, setup_sequencer},
+};
+use lee::{
+    PublicTransaction,
+    public_transaction::{Message, WitnessSet},
+};
+use sequencer_service_rpc::{RpcClient as _, SequencerClient, SequencerClientBuilder};
+use tokio::test;
+
+#[test]
+async fn user_origin_inbox_call_rejected() -> Result<()> {
+    let (_bedrock, bedrock_addr) = setup_bedrock_node()
+        .await
+        .context("Failed to set up Bedrock node")?;
+    let partial = SequencerPartialConfig::default();
+    let channel = config::bedrock_channel_id();
+    let (seq, _seq_home) = setup_sequencer(partial, bedrock_addr, vec![], channel, None)
+        .await
+        .context("Failed to set up sequencer")?;
+
+    // A user hand-builds a top-level inbox Dispatch and submits it via RPC.
+    let inbox_id = programs::cross_zone_inbox().id();
+    let msg = CrossZoneMessage {
+        src_zone: [2; 32],
+        src_block_id: 1,
+        src_tx_index: 0,
+        src_program_id: [9; 8],
+        target_program_id: programs::ping_receiver().id(),
+        payload: vec![],
+        l1_inclusion_witness: None,
+    };
+    let seen_id = inbox_seen_shard_account_id(inbox_id, &msg.src_zone, msg.src_block_id);
+    let message = Message::try_new(
+        inbox_id,
+        vec![inbox_config_account_id(inbox_id), seen_id],
+        vec![],
+        Instruction::Dispatch(msg),
+    )
+    .expect("build dispatch message");
+    let tx = LeeTransaction::Public(PublicTransaction::new(
+        message,
+        WitnessSet::from_raw_parts(vec![]),
+    ));
+
+    let result = sequencer_client(seq.addr())?.send_transaction(tx).await;
+    let err = result.expect_err("the sequencer must reject a user-origin inbox call");
+    assert!(
+        err.to_string().contains("sequencer-only"),
+        "rejection should cite the sequencer-only guard, got: {err}"
+    );
+    Ok(())
+}
+
+fn sequencer_client(addr: SocketAddr) -> Result<SequencerClient> {
+    let url = config::addr_to_url(config::UrlProtocol::Http, addr)
+        .context("Failed to build sequencer URL")?;
+    SequencerClientBuilder::default()
+        .build(url)
+        .context("Failed to build sequencer client")
+}

integration_tests/tests/cross_zone_ping.rs

@@ -0,0 +1,143 @@
+#![expect(
+    clippy::tests_outside_test_module,
+    reason = "top-level test functions are conventional for integration tests"
+)]
+
+//! End-to-end cross-zone round trip: a ping submitted on zone A is delivered by
+//! zone B's watcher to `ping_receiver` on zone B, which records the payload.
+//!
+//! Two sequencers share one Bedrock node (no indexers): zone A publishes the
+//! ping to Bedrock, zone B's watcher reads zone A's finalized blocks, injects the
+//! inbox dispatch, and zone B's sequencer delivers it. This is the M3 milestone,
+//! sequencer-trusted, with no indexer re-derivation (that is M4).
+
+use std::{net::SocketAddr, time::Duration};
+
+use anyhow::{Context as _, Result};
+use common::transaction::LeeTransaction;
+use cross_zone_outbox_core::outbox_pda;
+use integration_tests::{
+    config::{self, SequencerPartialConfig},
+    setup::{setup_bedrock_node, setup_sequencer},
+};
+use lee::{AccountId, PublicTransaction, public_transaction::Message};
+use lee_core::program::ProgramId;
+use ping_core::{ReceiverInstruction, SenderInstruction, ping_record_pda};
+use sequencer_core::config::{CrossZoneConfig, CrossZonePeer};
+use sequencer_service_rpc::{RpcClient as _, SequencerClient, SequencerClientBuilder};
+use tokio::test;
+
+const DELIVERY_TIMEOUT: Duration = Duration::from_secs(480);
+const PING_PAYLOAD: &[u8] = b"hello-cross-zone";
+
+#[test]
+async fn ping_crosses_from_zone_a_to_zone_b() -> Result<()> {
+    // Declared first so it outlives both zones (drops run in reverse order).
+    let (_bedrock, bedrock_addr) = setup_bedrock_node()
+        .await
+        .context("Failed to set up shared Bedrock node")?;
+
+    let partial = SequencerPartialConfig::default();
+    let channel_a = config::bedrock_channel_id();
+    let channel_b = config::bedrock_channel_id_b();
+    let zone_a: [u8; 32] = *channel_a.as_ref();
+    let zone_b: [u8; 32] = *channel_b.as_ref();
+
+    let receiver_id = programs::ping_receiver().id();
+
+    // Zone B watches zone A and allows delivery only to ping_receiver.
+    let cross_zone = CrossZoneConfig {
+        peers: vec![CrossZonePeer {
+            channel_id: zone_a,
+            allowed_targets: vec![receiver_id],
+            expected_block_signing_pubkey: None,
+        }],
+    };
+
+    let (seq_a, _seq_a_home) = setup_sequencer(partial, bedrock_addr, vec![], channel_a, None)
+        .await
+        .context("Failed to set up zone A sequencer")?;
+    let (seq_b, _seq_b_home) =
+        setup_sequencer(partial, bedrock_addr, vec![], channel_b, Some(cross_zone))
+            .await
+            .context("Failed to set up zone B sequencer")?;
+
+    // Submit the ping on zone A, addressed to ping_receiver on zone B.
+    let ping = build_ping_tx(zone_b, receiver_id);
+    sequencer_client(seq_a.addr())?
+        .send_transaction(ping)
+        .await
+        .context("Failed to submit ping on zone A")?;
+
+    // Wait until zone B's sequencer records the delivered payload.
+    let record_id = ping_record_pda(receiver_id);
+    let delivered = wait_for_delivery(sequencer_client(seq_b.addr())?, record_id).await?;
+
+    assert_eq!(
+        delivered, PING_PAYLOAD,
+        "Zone B must record the payload delivered from zone A"
+    );
+    Ok(())
+}
+
+/// Builds a top-level `ping_sender` transaction that chains into the outbox to emit
+/// a message carrying a `ping_receiver::Record` instruction for the target zone.
+fn build_ping_tx(target_zone: [u8; 32], receiver_id: ProgramId) -> LeeTransaction {
+    let outbox_id = programs::cross_zone_outbox().id();
+    let ordinal = 0;
+
+    // The payload is the ping_receiver instruction, serialized as risc0 words in
+    // little-endian bytes (the contract the inbox reverses when forwarding).
+    let words = risc0_zkvm::serde::to_vec(&ReceiverInstruction::Record {
+        payload: PING_PAYLOAD.to_vec(),
+    })
+    .expect("serialize ping instruction");
+    let payload: Vec<u8> = words.iter().flat_map(|word| word.to_le_bytes()).collect();
+
+    let send = SenderInstruction::Send {
+        outbox_program_id: outbox_id,
+        target_zone,
+        target_program_id: receiver_id,
+        target_accounts: vec![ping_record_pda(receiver_id).into_value()],
+        payload,
+        ordinal,
+    };
+
+    let outbox_account = outbox_pda(outbox_id, &target_zone, ordinal);
+    let message = Message::try_new(
+        programs::ping_sender().id(),
+        vec![outbox_account],
+        vec![],
+        send,
+    )
+    .expect("build ping message");
+    LeeTransaction::Public(PublicTransaction::new(
+        message,
+        lee::public_transaction::WitnessSet::from_raw_parts(vec![]),
+    ))
+}
+
+fn sequencer_client(addr: SocketAddr) -> Result<SequencerClient> {
+    let url = config::addr_to_url(config::UrlProtocol::Http, addr)
+        .context("Failed to build sequencer URL")?;
+    SequencerClientBuilder::default()
+        .build(url)
+        .context("Failed to build sequencer client")
+}
+
+/// Polls zone B's sequencer until the ping record PDA holds a payload.
+async fn wait_for_delivery(client: SequencerClient, record_id: AccountId) -> Result<Vec<u8>> {
+    let wait = async {
+        loop {
+            let account = client.get_account(record_id).await?;
+            let data = account.data.into_inner();
+            if !data.is_empty() {
+                return Ok::<Vec<u8>, anyhow::Error>(data);
+            }
+            tokio::time::sleep(Duration::from_secs(3)).await;
+        }
+    };
+    tokio::time::timeout(DELIVERY_TIMEOUT, wait)
+        .await
+        .context("Zone B did not record the cross-zone payload in time")?
+}

integration_tests/tests/cross_zone_state_machine.rs

@@ -0,0 +1,373 @@
+#![expect(
+    clippy::tests_outside_test_module,
+    reason = "top-level test functions are conventional for integration tests"
+)]
+
+//! Single-zone state-machine tests for cross-zone delivery (ping demo) and the
+//! wrapped-token bridge (Demo 2). They drive the guests in isolation, no watcher
+//! or Bedrock: a hand-built `cross_zone_inbox::Dispatch` (as the watcher would
+//! inject) and the source `bridge_lock::Lock` (which escrows and chains
+//! `outbox::Emit`). Fast, so they pin guest logic before the e2e exercises the
+//! plumbing. Run with `RISC0_DEV_MODE=1`.
+
+use std::collections::BTreeMap;
+
+use cross_zone_inbox_core::{
+    CrossZoneMessage, InboxConfig, Instruction as InboxInstruction, SeenShard,
+    inbox_config_account_id, inbox_seen_shard_account_id, message_key,
+};
+use cross_zone_outbox_core::{OutboxRecord, outbox_pda};
+use lee::{
+    AccountId, PrivateKey, PublicKey, PublicTransaction, V03State, ValidatedStateDiff,
+    public_transaction::{Message, WitnessSet},
+};
+use lee_core::account::Account;
+use ping_core::{ReceiverInstruction, ping_record_pda};
+
+const INITIAL_BALANCE: u128 = 100;
+const LOCK_AMOUNT: u128 = 30;
+const RECIPIENT: [u8; 32] = [9; 32];
+
+/// State registering the cross-zone builtins these tests exercise.
+fn base_state() -> V03State {
+    V03State::new().with_programs([
+        programs::cross_zone_inbox(),
+        programs::cross_zone_outbox(),
+        programs::ping_receiver(),
+        programs::bridge_lock(),
+        programs::wrapped_token(),
+    ])
+}
+
+/// Seeds an inbox config (inbox-owned) allowing `src_zone -> target`.
+fn seed_inbox_config(
+    state: &mut V03State,
+    self_zone: [u8; 32],
+    src_zone: [u8; 32],
+    target: lee_core::program::ProgramId,
+) {
+    let inbox_id = programs::cross_zone_inbox().id();
+    let mut allowed_targets = BTreeMap::new();
+    allowed_targets.insert(src_zone, vec![target]);
+    let config = InboxConfig {
+        self_zone,
+        allowed_peers: BTreeMap::new(),
+        allowed_targets,
+    };
+    state.insert_genesis_account(
+        inbox_config_account_id(inbox_id),
+        Account {
+            program_owner: inbox_id,
+            balance: 0,
+            data: config
+                .to_bytes()
+                .try_into()
+                .expect("config fits in account data"),
+            nonce: 0_u128.into(),
+        },
+    );
+}
+
+/// Seeds the wrapped-token config account pinning the inbox as authorized minter,
+/// matching what genesis seeds for a real zone.
+fn seed_wrapped_config(state: &mut V03State) {
+    let wrapped_token_id = programs::wrapped_token().id();
+    state.insert_genesis_account(
+        wrapped_token_core::config_account_id(wrapped_token_id),
+        Account {
+            program_owner: wrapped_token_id,
+            data: wrapped_token_core::minter_bytes(programs::cross_zone_inbox().id())
+                .to_vec()
+                .try_into()
+                .expect("minter id fits in account data"),
+            ..Default::default()
+        },
+    );
+}
+
+/// The wrapped-token `Mint` the bridge forwards, serialized as the cross-zone
+/// payload (risc0 words, little-endian bytes).
+fn mint_payload() -> Vec<u8> {
+    let mint = wrapped_token_core::Instruction::Mint {
+        recipient: RECIPIENT,
+        amount: LOCK_AMOUNT,
+    };
+    let words = risc0_zkvm::serde::to_vec(&mint).expect("serialize mint");
+    words.iter().flat_map(|word| word.to_le_bytes()).collect()
+}
+
+/// Drives `cross_zone_inbox::Dispatch` directly through the state machine
+/// (no watcher) and asserts the message is delivered to `ping_receiver`, which
+/// records the payload into its own PDA.
+#[test]
+fn inbox_dispatch_delivers_payload_to_ping_receiver() {
+    let inbox_id = programs::cross_zone_inbox().id();
+    let receiver_id = programs::ping_receiver().id();
+
+    let self_zone = [1_u8; 32];
+    let src_zone = [2_u8; 32];
+    let src_block_id = 5;
+
+    let mut state = base_state();
+    seed_inbox_config(&mut state, self_zone, src_zone, receiver_id);
+
+    // The payload is the ping_receiver instruction, serialized as risc0 words in
+    // little-endian bytes (the contract the inbox reverses when forwarding).
+    let inner = b"hello-cross-zone".to_vec();
+    let words = risc0_zkvm::serde::to_vec(&ReceiverInstruction::Record {
+        payload: inner.clone(),
+    })
+    .expect("serialize ping instruction");
+    let payload: Vec<u8> = words.iter().flat_map(|word| word.to_le_bytes()).collect();
+
+    let msg = CrossZoneMessage {
+        src_zone,
+        src_block_id,
+        src_tx_index: 0,
+        src_program_id: [9_u32; 8],
+        target_program_id: receiver_id,
+        payload,
+        l1_inclusion_witness: None,
+    };
+
+    let seen_id = inbox_seen_shard_account_id(inbox_id, &src_zone, src_block_id);
+    let record_id = ping_record_pda(receiver_id);
+
+    let message = Message::try_new(
+        inbox_id,
+        vec![inbox_config_account_id(inbox_id), seen_id, record_id],
+        vec![],
+        InboxInstruction::Dispatch(msg),
+    )
+    .expect("build dispatch message");
+    let tx = PublicTransaction::new(message, WitnessSet::from_raw_parts(vec![]));
+
+    let diff = ValidatedStateDiff::from_public_transaction(&tx, &state, 1, 0)
+        .expect("dispatch must validate and execute");
+    let record = diff
+        .public_diff()
+        .get(&record_id)
+        .expect("ping record account must change")
+        .clone();
+    assert_eq!(
+        record.data.into_inner(),
+        inner,
+        "ping_receiver must record the delivered payload"
+    );
+}
+
+/// Drives `bridge_lock::Lock` and asserts it debits the holder, credits the
+/// escrow, and records the forwarded mint in the outbox PDA.
+#[test]
+fn lock_escrows_balance_and_emits_to_outbox() {
+    let bridge_lock_id = programs::bridge_lock().id();
+    let wrapped_token_id = programs::wrapped_token().id();
+    let outbox_id = programs::cross_zone_outbox().id();
+    let zone_b = [2_u8; 32];
+    let ordinal = 0;
+
+    let mut state = base_state();
+
+    let holder_key = PrivateKey::try_new([7; 32]).expect("valid key");
+    let holder_id = AccountId::from(&PublicKey::new_from_private_key(&holder_key));
+    state.insert_genesis_account(
+        holder_id,
+        Account {
+            program_owner: bridge_lock_id,
+            balance: 0,
+            data: bridge_lock_core::balance_bytes(INITIAL_BALANCE)
+                .to_vec()
+                .try_into()
+                .expect("balance fits in account data"),
+            nonce: 0_u128.into(),
+        },
+    );
+
+    let payload = mint_payload();
+    let target_accounts = vec![
+        wrapped_token_core::config_account_id(wrapped_token_id).into_value(),
+        wrapped_token_core::holding_account_id(wrapped_token_id, &RECIPIENT).into_value(),
+    ];
+    let lock = bridge_lock_core::Instruction::Lock {
+        amount: LOCK_AMOUNT,
+        target_zone: zone_b,
+        target_program_id: wrapped_token_id,
+        target_accounts,
+        payload: payload.clone(),
+        outbox_program_id: outbox_id,
+        ordinal,
+    };
+
+    let escrow_id = bridge_lock_core::escrow_account_id(bridge_lock_id);
+    let outbox_record_id = outbox_pda(outbox_id, &zone_b, ordinal);
+    let message = Message::try_new(
+        bridge_lock_id,
+        vec![holder_id, escrow_id, outbox_record_id],
+        vec![0_u128.into()],
+        lock,
+    )
+    .expect("build lock message");
+    let witness = WitnessSet::for_message(&message, &[&holder_key]);
+    let tx = PublicTransaction::new(message, witness);
+
+    let diff = ValidatedStateDiff::from_public_transaction(&tx, &state, 1, 0)
+        .expect("lock must validate and execute");
+    let public_diff = diff.public_diff();
+
+    let holder_after =
+        bridge_lock_core::read_balance(&public_diff[&holder_id].data.clone().into_inner());
+    assert_eq!(
+        holder_after,
+        INITIAL_BALANCE - LOCK_AMOUNT,
+        "holder debited"
+    );
+
+    let escrow_after =
+        bridge_lock_core::read_balance(&public_diff[&escrow_id].data.clone().into_inner());
+    assert_eq!(escrow_after, LOCK_AMOUNT, "escrow credited");
+
+    let record =
+        OutboxRecord::from_bytes(&public_diff[&outbox_record_id].data.clone().into_inner())
+            .expect("outbox PDA holds an OutboxRecord");
+    assert_eq!(record.target_zone, zone_b);
+    assert_eq!(record.target_program_id, wrapped_token_id);
+    assert_eq!(
+        record.payload, payload,
+        "emitted payload is the wrapped mint"
+    );
+}
+
+/// Drives a hand-built `cross_zone_inbox::Dispatch` (as the watcher would inject)
+/// and asserts it chains into `wrapped_token::Mint`, crediting the recipient.
+#[test]
+fn inbox_dispatch_mints_wrapped_token() {
+    let inbox_id = programs::cross_zone_inbox().id();
+    let wrapped_token_id = programs::wrapped_token().id();
+
+    let self_zone = [1_u8; 32];
+    let src_zone = [2_u8; 32];
+    let src_block_id = 5;
+
+    let mut state = base_state();
+    seed_inbox_config(&mut state, self_zone, src_zone, wrapped_token_id);
+    seed_wrapped_config(&mut state);
+
+    let msg = CrossZoneMessage {
+        src_zone,
+        src_block_id,
+        src_tx_index: 0,
+        src_program_id: [9_u32; 8],
+        target_program_id: wrapped_token_id,
+        payload: mint_payload(),
+        l1_inclusion_witness: None,
+    };
+
+    let seen_id = inbox_seen_shard_account_id(inbox_id, &src_zone, src_block_id);
+    let wrapped_config_id = wrapped_token_core::config_account_id(wrapped_token_id);
+    let holding_id = wrapped_token_core::holding_account_id(wrapped_token_id, &RECIPIENT);
+
+    let message = Message::try_new(
+        inbox_id,
+        vec![
+            inbox_config_account_id(inbox_id),
+            seen_id,
+            wrapped_config_id,
+            holding_id,
+        ],
+        vec![],
+        InboxInstruction::Dispatch(msg),
+    )
+    .expect("build dispatch message");
+    let tx = PublicTransaction::new(message, WitnessSet::from_raw_parts(vec![]));
+
+    let diff = ValidatedStateDiff::from_public_transaction(&tx, &state, 1, 0)
+        .expect("dispatch must validate and execute");
+    let minted = wrapped_token_core::read_balance(
+        &diff.public_diff()[&holding_id].data.clone().into_inner(),
+    );
+    assert_eq!(
+        minted, LOCK_AMOUNT,
+        "recipient holding minted the locked amount"
+    );
+}
+
+/// A dispatch whose message key is already in the seen-shard is an idempotent
+/// no-op: the inbox makes no chained call, so the wrapped token is not minted a
+/// second time. This is the bridge's replay defense.
+#[test]
+fn mint_replay_rejected() {
+    let inbox_id = programs::cross_zone_inbox().id();
+    let wrapped_token_id = programs::wrapped_token().id();
+
+    let self_zone = [1_u8; 32];
+    let src_zone = [2_u8; 32];
+    let src_block_id = 5;
+    let src_tx_index = 0;
+
+    let mut state = base_state();
+    seed_inbox_config(&mut state, self_zone, src_zone, wrapped_token_id);
+    seed_wrapped_config(&mut state);
+
+    // Seed the seen-shard as already containing this message's key, so the inbox
+    // takes the replay no-op branch. The shard is inbox-owned (claimed on a prior
+    // delivery), so the guest leaves it untouched.
+    let seen_id = inbox_seen_shard_account_id(inbox_id, &src_zone, src_block_id);
+    let mut shard = SeenShard::default();
+    shard.insert(message_key(&src_zone, src_block_id, src_tx_index));
+    state.insert_genesis_account(
+        seen_id,
+        Account {
+            program_owner: inbox_id,
+            balance: 0,
+            data: shard
+                .to_bytes()
+                .try_into()
+                .expect("shard fits in account data"),
+            nonce: 0_u128.into(),
+        },
+    );
+
+    let msg = CrossZoneMessage {
+        src_zone,
+        src_block_id,
+        src_tx_index,
+        src_program_id: [9_u32; 8],
+        target_program_id: wrapped_token_id,
+        payload: mint_payload(),
+        l1_inclusion_witness: None,
+    };
+
+    let wrapped_config_id = wrapped_token_core::config_account_id(wrapped_token_id);
+    let holding_id = wrapped_token_core::holding_account_id(wrapped_token_id, &RECIPIENT);
+
+    let message = Message::try_new(
+        inbox_id,
+        vec![
+            inbox_config_account_id(inbox_id),
+            seen_id,
+            wrapped_config_id,
+            holding_id,
+        ],
+        vec![],
+        InboxInstruction::Dispatch(msg),
+    )
+    .expect("build dispatch message");
+    let tx = PublicTransaction::new(message, WitnessSet::from_raw_parts(vec![]));
+
+    let diff = ValidatedStateDiff::from_public_transaction(&tx, &state, 1, 0)
+        .expect("a replayed dispatch is a valid no-op, not an error");
+    let public_diff = diff.public_diff();
+
+    // No mint: the holding is never credited on replay.
+    let minted = public_diff.get(&holding_id).map_or(0, |account| {
+        wrapped_token_core::read_balance(&account.data.clone().into_inner())
+    });
+    assert_eq!(minted, 0, "a replayed message must not mint again");
+
+    // The seen-shard is untouched by the no-op.
+    if let Some(seen) = public_diff.get(&seen_id) {
+        let shard_after =
+            SeenShard::from_bytes(&seen.data.clone().into_inner()).expect("seen shard decodes");
+        assert_eq!(shard_after, shard, "replay must not modify the seen-shard");
+    }
+}

integration_tests/tests/cross_zone_verified.rs

@@ -0,0 +1,162 @@
+#![expect(
+    clippy::tests_outside_test_module,
+    reason = "top-level test functions are conventional for integration tests"
+)]
+
+//! Cross-zone round trip with the indexer in the loop (Option B). A ping on zone
+//! A is delivered to zone B, and zone B's indexer independently re-derives the
+//! injected dispatch from zone A's finalized blocks before applying it. The
+//! payload landing in the indexer's state proves verification passed; a forgery
+//! would have halted the indexer instead.
+
+use std::{net::SocketAddr, time::Duration};
+
+use anyhow::{Context as _, Result};
+use common::transaction::LeeTransaction;
+use cross_zone_outbox_core::outbox_pda;
+use integration_tests::{
+    config::{self, SequencerPartialConfig},
+    indexer_client::IndexerClient,
+    setup::{setup_bedrock_node, setup_indexer, setup_sequencer},
+};
+use lee::{AccountId, PublicTransaction, public_transaction::Message};
+use lee_core::program::ProgramId;
+use ping_core::{ReceiverInstruction, SenderInstruction, ping_record_pda};
+use sequencer_core::config::{CrossZoneConfig, CrossZonePeer};
+use sequencer_service_rpc::{RpcClient as _, SequencerClient, SequencerClientBuilder};
+use tokio::test;
+
+const DELIVERY_TIMEOUT: Duration = Duration::from_secs(600);
+const PING_PAYLOAD: &[u8] = b"hello-verified-zone";
+
+#[test]
+async fn indexer_verifies_and_delivers_cross_zone_ping() -> Result<()> {
+    // Declared first so it outlives both zones (drops run in reverse order).
+    let (_bedrock, bedrock_addr) = setup_bedrock_node()
+        .await
+        .context("Failed to set up shared Bedrock node")?;
+
+    let partial = SequencerPartialConfig::default();
+    let channel_a = config::bedrock_channel_id();
+    let channel_b = config::bedrock_channel_id_b();
+    let zone_a: [u8; 32] = *channel_a.as_ref();
+    let zone_b: [u8; 32] = *channel_b.as_ref();
+
+    let receiver_id = programs::ping_receiver().id();
+    let cross_zone = CrossZoneConfig {
+        peers: vec![CrossZonePeer {
+            channel_id: zone_a,
+            allowed_targets: vec![receiver_id],
+            expected_block_signing_pubkey: None,
+        }],
+    };
+
+    // Zone A: source. Zone B: destination, with the watcher on its sequencer and
+    // the verifier on its indexer.
+    let (seq_a, _seq_a_home) = setup_sequencer(partial, bedrock_addr, vec![], channel_a, None)
+        .await
+        .context("Failed to set up zone A sequencer")?;
+    let (_idx_a, _idx_a_home) = setup_indexer(bedrock_addr, channel_a, None)
+        .await
+        .context("Failed to set up zone A indexer")?;
+    let (_seq_b, _seq_b_home) = setup_sequencer(
+        partial,
+        bedrock_addr,
+        vec![],
+        channel_b,
+        Some(cross_zone.clone()),
+    )
+    .await
+    .context("Failed to set up zone B sequencer")?;
+    let (idx_b, _idx_b_home) = setup_indexer(bedrock_addr, channel_b, Some(cross_zone))
+        .await
+        .context("Failed to set up zone B indexer")?;
+
+    // Submit the ping on zone A, addressed to ping_receiver on zone B.
+    let ping = build_ping_tx(zone_b, receiver_id);
+    sequencer_client(seq_a.addr())?
+        .send_transaction(ping)
+        .await
+        .context("Failed to submit ping on zone A")?;
+
+    // Wait until zone B's indexer records the delivered payload. The indexer only
+    // applies the dispatch after re-deriving and verifying it.
+    let record_id = ping_record_pda(receiver_id);
+    let indexer_url = config::addr_to_url(config::UrlProtocol::Ws, idx_b.addr())
+        .context("Failed to build indexer URL")?;
+    let indexer = IndexerClient::new(&indexer_url)
+        .await
+        .context("Failed to build indexer client")?;
+
+    let delivered = wait_for_indexer_delivery(&indexer, record_id).await?;
+    assert_eq!(
+        delivered, PING_PAYLOAD,
+        "Zone B's indexer must record the verified cross-zone payload"
+    );
+    Ok(())
+}
+
+fn build_ping_tx(target_zone: [u8; 32], receiver_id: ProgramId) -> LeeTransaction {
+    let outbox_id = programs::cross_zone_outbox().id();
+    let ordinal = 0;
+
+    let words = risc0_zkvm::serde::to_vec(&ReceiverInstruction::Record {
+        payload: PING_PAYLOAD.to_vec(),
+    })
+    .expect("serialize ping instruction");
+    let payload: Vec<u8> = words.iter().flat_map(|word| word.to_le_bytes()).collect();
+
+    let send = SenderInstruction::Send {
+        outbox_program_id: outbox_id,
+        target_zone,
+        target_program_id: receiver_id,
+        target_accounts: vec![ping_record_pda(receiver_id).into_value()],
+        payload,
+        ordinal,
+    };
+
+    let outbox_account = outbox_pda(outbox_id, &target_zone, ordinal);
+    let message = Message::try_new(
+        programs::ping_sender().id(),
+        vec![outbox_account],
+        vec![],
+        send,
+    )
+    .expect("build ping message");
+    LeeTransaction::Public(PublicTransaction::new(
+        message,
+        lee::public_transaction::WitnessSet::from_raw_parts(vec![]),
+    ))
+}
+
+fn sequencer_client(addr: SocketAddr) -> Result<SequencerClient> {
+    let url = config::addr_to_url(config::UrlProtocol::Http, addr)
+        .context("Failed to build sequencer URL")?;
+    SequencerClientBuilder::default()
+        .build(url)
+        .context("Failed to build sequencer client")
+}
+
+/// Polls zone B's indexer until the ping record PDA holds a payload.
+async fn wait_for_indexer_delivery(
+    indexer: &IndexerClient,
+    record_id: AccountId,
+) -> Result<Vec<u8>> {
+    let account_id = indexer_service_protocol::AccountId {
+        value: record_id.into_value(),
+    };
+    let wait = async {
+        loop {
+            let account =
+                indexer_service_rpc::RpcClient::get_account(&**indexer, account_id).await?;
+            let data = account.data.0;
+            if !data.is_empty() {
+                return Ok::<Vec<u8>, anyhow::Error>(data);
+            }
+            tokio::time::sleep(Duration::from_secs(3)).await;
+        }
+    };
+    tokio::time::timeout(DELIVERY_TIMEOUT, wait)
+        .await
+        .context("Zone B's indexer did not record the payload in time")?
+}

integration_tests/tests/indexer_ffi_helpers/mod.rs

@@ -50,8 +50,12 @@ pub fn setup_indexer_ffi(bedrock_addr: SocketAddr) -> Result<(IndexerServiceFFI,
         temp_indexer_dir.path().display()
     );
 
-    let indexer_config = integration_tests::config::indexer_config(bedrock_addr)
-        .context("Failed to create Indexer config")?;
+    let indexer_config = integration_tests::config::indexer_config(
+        bedrock_addr,
+        integration_tests::config::bedrock_channel_id(),
+        None,
+    )
+    .context("Failed to create Indexer config")?;
 
     let config_json = serde_json::to_vec(&indexer_config)?;
     let config_path = temp_indexer_dir.path().join("indexer_config.json");

integration_tests/tests/two_zone.rs

@@ -0,0 +1,110 @@
+#![expect(
+    clippy::tests_outside_test_module,
+    reason = "top-level test functions are conventional for integration tests"
+)]
+
+//! Two zones (sequencer + indexer each, on separate channels) sharing one
+//! Bedrock node, each producing and finalizing blocks independently.
+
+use std::{net::SocketAddr, time::Duration};
+
+use anyhow::{Context as _, Result};
+use indexer_service_rpc::RpcClient as _;
+use integration_tests::{
+    config::{self, SequencerPartialConfig},
+    indexer_client::IndexerClient,
+    setup::{setup_bedrock_node, setup_indexer, setup_sequencer},
+};
+use sequencer_service_rpc::{RpcClient as _, SequencerClientBuilder};
+use tokio::test;
+
+const ZONE_LIVE_TIMEOUT: Duration = Duration::from_secs(360);
+
+// Genesis is block 1, so reaching 2 means a block was produced past it.
+const MIN_BLOCK_ID: u64 = 2;
+
+#[test]
+async fn two_zones_share_one_bedrock_and_both_advance() -> Result<()> {
+    // Declared first so it outlives both zones (drops run in reverse order).
+    let (_bedrock, bedrock_addr) = setup_bedrock_node()
+        .await
+        .context("Failed to set up shared Bedrock node")?;
+
+    let partial = SequencerPartialConfig::default();
+    let channel_a = config::bedrock_channel_id();
+    let channel_b = config::bedrock_channel_id_b();
+
+    // Empty genesis is enough: the clock transaction drives block production.
+    let (seq_a, _seq_a_home) = setup_sequencer(partial, bedrock_addr, vec![], channel_a, None)
+        .await
+        .context("Failed to set up zone A sequencer")?;
+    let (idx_a, _idx_a_home) = setup_indexer(bedrock_addr, channel_a, None)
+        .await
+        .context("Failed to set up zone A indexer")?;
+    let (seq_b, _seq_b_home) = setup_sequencer(partial, bedrock_addr, vec![], channel_b, None)
+        .await
+        .context("Failed to set up zone B sequencer")?;
+    let (idx_b, _idx_b_home) = setup_indexer(bedrock_addr, channel_b, None)
+        .await
+        .context("Failed to set up zone B indexer")?;
+
+    let (height_a, height_b) = tokio::try_join!(
+        wait_until_zone_live("A", seq_a.addr(), idx_a.addr()),
+        wait_until_zone_live("B", seq_b.addr(), idx_b.addr()),
+    )?;
+
+    assert!(
+        height_a >= MIN_BLOCK_ID,
+        "Zone A indexer only reached block {height_a}, expected >= {MIN_BLOCK_ID}"
+    );
+    assert!(
+        height_b >= MIN_BLOCK_ID,
+        "Zone B indexer only reached block {height_b}, expected >= {MIN_BLOCK_ID}"
+    );
+
+    Ok(())
+}
+
+/// Wait for the sequencer to produce past genesis and the indexer to finalize up
+/// to it. Returns the indexer's finalized block id.
+async fn wait_until_zone_live(
+    label: &str,
+    sequencer_addr: SocketAddr,
+    indexer_addr: SocketAddr,
+) -> Result<u64> {
+    let sequencer_url = config::addr_to_url(config::UrlProtocol::Http, sequencer_addr)
+        .context("Failed to build sequencer URL")?;
+    let sequencer = SequencerClientBuilder::default()
+        .build(sequencer_url)
+        .context("Failed to build sequencer client")?;
+
+    let indexer_url = config::addr_to_url(config::UrlProtocol::Ws, indexer_addr)
+        .context("Failed to build indexer URL")?;
+    let indexer = IndexerClient::new(&indexer_url)
+        .await
+        .context("Failed to build indexer client")?;
+
+    let wait = async {
+        loop {
+            if sequencer.get_last_block_id().await? >= MIN_BLOCK_ID {
+                break;
+            }
+            tokio::time::sleep(Duration::from_secs(2)).await;
+        }
+        let target = sequencer.get_last_block_id().await?;
+        loop {
+            let finalized = indexer.get_last_finalized_block_id().await?.unwrap_or(0);
+            if finalized >= target {
+                log::info!(
+                    "Zone {label} live: sequencer at {target}, indexer finalized {finalized}"
+                );
+                return Ok::<u64, anyhow::Error>(finalized);
+            }
+            tokio::time::sleep(Duration::from_secs(2)).await;
+        }
+    };
+
+    tokio::time::timeout(ZONE_LIVE_TIMEOUT, wait)
+        .await
+        .with_context(|| format!("Zone {label} did not become live within {ZONE_LIVE_TIMEOUT:?}"))?
+}

lee/state_machine/src/state/mod.rs

@@ -194,6 +194,14 @@ impl V03State {
         self.programs.insert(program.id(), program);
     }
 
+    /// Seeds a single genesis account that is not produced by any transaction
+    /// (e.g. the cross-zone inbox config or a bridge-lock holding). Lets the
+    /// sequencer and indexer seed identical zone-specific state after building
+    /// the shared initial state.
+    pub fn insert_genesis_account(&mut self, account_id: AccountId, account: Account) {
+        self.public_state.insert(account_id, account);
+    }
+
     pub fn apply_state_diff(&mut self, diff: ValidatedStateDiff) {
         let StateDiff {
             signer_account_ids,

lez/common/src/block.rs

@@ -68,6 +68,16 @@ impl Block {
         }
         .compute_hash()
     }
+
+    /// Recomputes the signed hash from the block contents and checks the header
+    /// signature against `expected_pubkey`. Used to pin a peer zone's
+    /// block-signing key, so a block inscribed by anyone other than that zone's
+    /// sequencer is rejected even if it reached the channel.
+    #[must_use]
+    pub fn is_signed_by(&self, expected_pubkey: &lee::PublicKey) -> bool {
+        let hash = HashableBlockData::from(self.clone()).compute_hash();
+        self.header.signature.is_valid_for(&hash.0, expected_pubkey)
+    }
 }
 
 impl Serialize for Block {

lez/cross_zone/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "cross_zone"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee.workspace = true
+lee_core.workspace = true
+programs.workspace = true
+cross_zone_inbox_core.workspace = true
+bridge_lock_core.workspace = true
+ping_core.workspace = true
+risc0-zkvm.workspace = true

lez/cross_zone/src/lib.rs

@@ -0,0 +1,189 @@
+//! Host-side cross-zone helpers that need program ids (`programs`) or the state
+//! machine (`lee`), kept out of the guest-pure cores. Mirrors `system_accounts`:
+//! it resolves builtin program ids and bakes them into transactions and genesis
+//! accounts for the watcher (sequencer) and verifier (indexer).
+
+use std::collections::BTreeMap;
+
+pub use cross_zone_inbox_core::{CrossZoneConfig, CrossZonePeer};
+use cross_zone_inbox_core::{
+    CrossZoneMessage, InboxConfig, Instruction, ZoneId, inbox_config_account_id,
+    inbox_seen_shard_account_id,
+};
+use lee_core::{
+    account::{Account, AccountId},
+    program::ProgramId,
+};
+
+/// The cross-zone emission fields a watcher or verifier reads off a source
+/// transaction, common to every emitter program.
+pub struct Emission {
+    pub target_zone: ZoneId,
+    pub target_program_id: ProgramId,
+    pub target_accounts: Vec<[u8; 32]>,
+    pub payload: Vec<u8>,
+}
+
+/// Whether a program may only be invoked by sequencer-origin transactions.
+///
+/// The cross-zone inbox is injected solely by the watcher; a user-submitted call
+/// must be rejected at ingress, since `TransactionOrigin` is not carried in the
+/// block.
+#[must_use]
+pub fn is_sequencer_only_program(program_id: ProgramId) -> bool {
+    program_id == programs::cross_zone_inbox().id()
+}
+
+/// Extracts the cross-zone emission from a source transaction.
+///
+/// Recognizes the known emitter programs (`ping_sender`, `bridge_lock`). The
+/// watcher and verifier both use this so they agree on what a given source tx
+/// emits.
+#[must_use]
+pub fn extract_emission(program_id: ProgramId, instruction_data: &[u32]) -> Option<Emission> {
+    if program_id == programs::ping_sender().id() {
+        let ping_core::SenderInstruction::Send {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ..
+        } = risc0_zkvm::serde::from_slice(instruction_data).ok()?;
+        Some(Emission {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+        })
+    } else if program_id == programs::bridge_lock().id() {
+        let bridge_lock_core::Instruction::Lock {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ..
+        } = risc0_zkvm::serde::from_slice(instruction_data).ok()?;
+        Some(Emission {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+        })
+    } else {
+        None
+    }
+}
+
+/// Builds the sequencer-origin dispatch transaction. Pure for fixed inputs, so
+/// the watcher's injected tx and the indexer's re-derived tx are byte-identical.
+fn build_inbox_dispatch_tx(
+    inbox_id: ProgramId,
+    msg: &CrossZoneMessage,
+    target_account_ids: Vec<AccountId>,
+) -> lee::PublicTransaction {
+    let mut account_ids = Vec::with_capacity(target_account_ids.len().saturating_add(2));
+    account_ids.push(inbox_config_account_id(inbox_id));
+    account_ids.push(inbox_seen_shard_account_id(
+        inbox_id,
+        &msg.src_zone,
+        msg.src_block_id,
+    ));
+    account_ids.extend(target_account_ids);
+
+    let message = lee::public_transaction::Message::try_new(
+        inbox_id,
+        account_ids,
+        vec![],
+        Instruction::Dispatch(msg.clone()),
+    )
+    .expect("inbox dispatch instruction must serialize");
+
+    lee::PublicTransaction::new(
+        message,
+        lee::public_transaction::WitnessSet::from_raw_parts(vec![]),
+    )
+}
+
+/// Builds the dispatch transaction for one peer emission.
+///
+/// Both the sequencer's watcher and the indexer's verifier go through this so
+/// their transactions are byte-identical for the same emission (the basis of the
+/// Option B check).
+#[must_use]
+pub fn build_dispatch_from_emission(
+    src_zone: ZoneId,
+    src_block_id: u64,
+    src_tx_index: u32,
+    src_program_id: ProgramId,
+    target_program_id: ProgramId,
+    target_accounts: &[[u8; 32]],
+    payload: Vec<u8>,
+) -> lee::PublicTransaction {
+    let msg = CrossZoneMessage {
+        src_zone,
+        src_block_id,
+        src_tx_index,
+        src_program_id,
+        target_program_id,
+        payload,
+        l1_inclusion_witness: None,
+    };
+    let target_ids = target_accounts
+        .iter()
+        .copied()
+        .map(AccountId::new)
+        .collect();
+    build_inbox_dispatch_tx(programs::cross_zone_inbox().id(), &msg, target_ids)
+}
+
+/// Builds the inbox config account a zone seeds into genesis state.
+///
+/// Lets the inbox guest authorize inbound peer messages. The sequencer and
+/// indexer seed the same account from the same config, keeping their replayed
+/// state consistent.
+#[must_use]
+pub fn build_inbox_config_account(
+    self_zone: ZoneId,
+    cross_zone: &CrossZoneConfig,
+) -> (AccountId, Account) {
+    let inbox_id = programs::cross_zone_inbox().id();
+
+    let mut allowed_targets = BTreeMap::new();
+    for peer in &cross_zone.peers {
+        allowed_targets.insert(peer.channel_id, peer.allowed_targets.clone());
+    }
+    let config = InboxConfig {
+        self_zone,
+        allowed_peers: BTreeMap::new(),
+        allowed_targets,
+    };
+
+    let account = Account {
+        program_owner: inbox_id,
+        balance: 0,
+        data: config
+            .to_bytes()
+            .try_into()
+            .expect("inbox config fits in account data"),
+        nonce: 0_u128.into(),
+    };
+    (inbox_config_account_id(inbox_id), account)
+}
+
+/// Builds the genesis holding account funding a holder's bridgeable balance.
+///
+/// Owned by `bridge_lock`, data is the LE balance. Not produced by any
+/// transaction, so the sequencer and indexer both seed it through this one
+/// builder.
+#[must_use]
+pub fn build_holding_account(holder: AccountId, amount: u128) -> (AccountId, Account) {
+    let account = Account {
+        program_owner: programs::bridge_lock().id(),
+        data: bridge_lock_core::balance_bytes(amount)
+            .to_vec()
+            .try_into()
+            .expect("balance fits in account data"),
+        ..Default::default()
+    };
+    (holder, account)
+}

lez/indexer/core/Cargo.toml

@@ -16,6 +16,9 @@ common.workspace = true
 logos-blockchain-zone-sdk.workspace = true
 lee.workspace = true
 lee_core.workspace = true
+cross_zone.workspace = true
+cross_zone_inbox_core.workspace = true
+programs.workspace = true
 storage.workspace = true
 testnet_initial_state.workspace = true
 
@@ -32,6 +35,9 @@ serde_json.workspace = true
 thiserror.workspace = true
 async-stream.workspace = true
 tokio.workspace = true
+risc0-zkvm.workspace = true
+hex.workspace = true
 
 [dev-dependencies]
 tempfile.workspace = true
+ping_core.workspace = true

lez/indexer/core/src/block_store.rs

@@ -45,13 +45,19 @@ pub struct IndexerStore {
 impl IndexerStore {
     /// Starting database at the start of new chain.
     /// Creates files if necessary.
-    pub fn open_db(location: &Path) -> Result<Self> {
+    pub fn open_db(location: &Path, genesis_seed: Vec<(AccountId, Account)>) -> Result<Self> {
         #[cfg(not(feature = "testnet"))]
-        let initial_state = testnet_initial_state::initial_state();
+        let mut initial_state = testnet_initial_state::initial_state();
 
         #[cfg(feature = "testnet")]
-        let initial_state = testnet_initial_state::initial_state_testnet();
+        let mut initial_state = testnet_initial_state::initial_state_testnet();
 
+        // Seed any zone-specific genesis accounts (the cross-zone inbox config and
+        // bridge-lock holdings) so the indexer's replayed state matches the
+        // sequencer's; none are produced by a transaction.
+        for (account_id, account) in genesis_seed {
+            initial_state.insert_genesis_account(account_id, account);
+        }
         let dbio = RocksDBIO::open_or_create(location, &initial_state)?;
 
         let current_state = dbio.final_state()?;
@@ -394,7 +400,7 @@ mod stall_reason_tests {
     #[tokio::test]
     async fn stall_reason_roundtrips_and_clears() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         assert!(store.get_stall_reason().expect("get").is_none());
 
@@ -441,7 +447,7 @@ mod tests {
     fn correct_startup() {
         let home = tempdir().unwrap();
 
-        let storage = IndexerStore::open_db(home.as_ref()).unwrap();
+        let storage = IndexerStore::open_db(home.as_ref(), Vec::new()).unwrap();
 
         let final_id = storage.get_last_block_id().unwrap();
 
@@ -451,7 +457,7 @@ mod tests {
     #[tokio::test]
     async fn accept_block_applies_transfers_and_advances_tip() {
         let home = tempdir().unwrap();
-        let store = IndexerStore::open_db(home.as_ref()).unwrap();
+        let store = IndexerStore::open_db(home.as_ref(), Vec::new()).unwrap();
 
         let initial_accounts = initial_pub_accounts_private_keys();
         let from = initial_accounts[0].account_id;
@@ -493,7 +499,7 @@ mod tests {
     #[tokio::test]
     async fn account_state_at_block_reflects_history() {
         let home = tempdir().unwrap();
-        let store = IndexerStore::open_db(home.as_ref()).unwrap();
+        let store = IndexerStore::open_db(home.as_ref(), Vec::new()).unwrap();
 
         let initial_accounts = initial_pub_accounts_private_keys();
         let from = initial_accounts[0].account_id;
@@ -559,7 +565,7 @@ mod accept_tests {
     #[tokio::test]
     async fn non_genesis_first_block_parks_with_unexpected_id() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let block = valid_hash_block(2, HashType([0_u8; 32]));
         let outcome = store
@@ -582,7 +588,7 @@ mod accept_tests {
     #[tokio::test]
     async fn hash_mismatch_parks() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let mut block = valid_hash_block(1, HashType([0_u8; 32]));
         block.header.timestamp = 999; // invalidates the stored hash
@@ -600,7 +606,7 @@ mod accept_tests {
     #[tokio::test]
     async fn second_break_bumps_orphan_count_and_keeps_first() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let first = valid_hash_block(2, HashType([0_u8; 32]));
         store
@@ -621,7 +627,7 @@ mod accept_tests {
     #[tokio::test]
     async fn deserialize_break_records_stall_without_header() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         store
             .record_stall(
@@ -639,7 +645,7 @@ mod accept_tests {
     #[tokio::test]
     async fn parks_then_recovers_on_valid_continuation() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         // Genesis (block 1, clock-only) applies and advances the tip.
         let genesis = produce_dummy_block(1, None, vec![]);
@@ -687,7 +693,7 @@ mod accept_tests {
     #[tokio::test]
     async fn accept_block_records_tip_inscription_slot() {
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         assert_eq!(store.get_tip_slot().expect("get"), None);
 
@@ -729,7 +735,7 @@ mod accept_tests {
         use testnet_initial_state::initial_pub_accounts_private_keys;
 
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let accounts = initial_pub_accounts_private_keys();
         let from = accounts[0].account_id;
@@ -779,7 +785,7 @@ mod accept_tests {
         use testnet_initial_state::initial_pub_accounts_private_keys;
 
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let accounts = initial_pub_accounts_private_keys();
         let from = accounts[0].account_id;
@@ -839,7 +845,7 @@ mod accept_tests {
         use testnet_initial_state::initial_pub_accounts_private_keys;
 
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let accounts = initial_pub_accounts_private_keys();
         let from = accounts[0].account_id;
@@ -876,7 +882,7 @@ mod accept_tests {
 
         // The #605 restart: reopening past the boundary must work.
         drop(store);
-        let reopened = IndexerStore::open_db(dir.path()).expect("reopen");
+        let reopened = IndexerStore::open_db(dir.path(), Vec::new()).expect("reopen");
         assert_eq!(reopened.last_block().unwrap(), Some(101));
     }
 
@@ -885,7 +891,7 @@ mod accept_tests {
         use testnet_initial_state::initial_pub_accounts_private_keys;
 
         let dir = tempfile::tempdir().expect("tempdir");
-        let store = IndexerStore::open_db(dir.path()).expect("open store");
+        let store = IndexerStore::open_db(dir.path(), Vec::new()).expect("open store");
 
         let accounts = initial_pub_accounts_private_keys();
         let from = accounts[0].account_id;

lez/indexer/core/src/chain_consistency.rs

@@ -319,6 +319,8 @@ mod tests {
             },
             channel_id: ChannelId::from([1; 32]),
             allow_chain_reset: false,
+            cross_zone: None,
+            bridge_lock_holdings: Vec::new(),
         };
         IndexerCore::open(config, dir).expect("open core")
     }

lez/indexer/core/src/config.rs

@@ -2,7 +2,9 @@ use std::{fs::File, io::BufReader, path::Path, time::Duration};
 
 use anyhow::{Context as _, Result};
 use common::config::BasicAuth;
+use cross_zone_inbox_core::CrossZoneConfig;
 use humantime_serde;
+use lee::AccountId;
 pub use logos_blockchain_core::mantle::ops::channel::ChannelId;
 use serde::{Deserialize, Serialize};
 use url::Url;
@@ -20,6 +22,14 @@ pub struct IndexerConfig {
     pub consensus_info_polling_interval: Duration,
     pub bedrock_config: ClientConfig,
     pub channel_id: ChannelId,
+    /// Cross-zone configuration. `None` disables the indexer's cross-zone handling.
+    #[serde(default)]
+    pub cross_zone: Option<CrossZoneConfig>,
+    /// Bridge-lock holdings to seed into genesis, mirroring the sequencer's
+    /// `SupplyBridgeLockHolding` actions. They are not produced by any
+    /// transaction, so the indexer must seed them to match the sequencer's state.
+    #[serde(default)]
+    pub bridge_lock_holdings: Vec<BridgeLockHolding>,
     /// Whether to wipe the indexer store and re-index from scratch when the startup
     /// chain-identity check finds the channel serving a different block than the one
     /// stored at the same id.
@@ -29,6 +39,14 @@ pub struct IndexerConfig {
     pub allow_chain_reset: bool,
 }
 
+/// A genesis-funded bridge-lock holder balance, configured identically on the
+/// sequencer (via `SupplyBridgeLockHolding`) and the indexer.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct BridgeLockHolding {
+    pub holder: AccountId,
+    pub amount: u128,
+}
+
 impl IndexerConfig {
     pub fn from_path(config_path: &Path) -> Result<Self> {
         let file = File::open(config_path).with_context(|| {

lez/indexer/core/src/cross_zone_verifier.rs

@@ -0,0 +1,500 @@
+use std::{
+    collections::{HashMap, HashSet},
+    sync::Arc,
+    time::Duration,
+};
+
+use anyhow::{Result, bail};
+use common::{block::Block, transaction::LeeTransaction};
+use cross_zone::{build_dispatch_from_emission, extract_emission};
+use cross_zone_inbox_core::{
+    CrossZoneMessage, Instruction as InboxInstruction, MessageKey, ZoneId, message_key,
+};
+use futures::StreamExt as _;
+use lee::PublicKey;
+use log::{error, info};
+use logos_blockchain_core::mantle::ops::channel::ChannelId;
+use logos_blockchain_zone_sdk::{
+    CommonHttpClient, ZoneMessage, adapter::NodeHttpClient, indexer::ZoneIndexer,
+};
+use tokio::sync::RwLock;
+
+use crate::config::IndexerConfig;
+
+/// How often the verifier logs that it is still waiting on a lagging peer reader,
+/// so a stuck wait is observable without rejecting a legitimate message.
+const LAG_LOG_INTERVAL: Duration = Duration::from_secs(30);
+
+/// Cache of finalized peer-zone blocks, filled by per-peer reader tasks and read
+/// by the verifier to re-derive cross-zone dispatch transactions.
+#[derive(Clone, Default)]
+struct PeerBlocks {
+    chains: Arc<RwLock<HashMap<ZoneId, HashMap<u64, Block>>>>,
+}
+
+impl PeerBlocks {
+    async fn insert(&self, zone: ZoneId, block: Block) {
+        self.chains
+            .write()
+            .await
+            .entry(zone)
+            .or_default()
+            .insert(block.header.block_id, block);
+    }
+
+    async fn get(&self, zone: ZoneId, block_id: u64) -> Option<Block> {
+        self.chains
+            .read()
+            .await
+            .get(&zone)
+            .and_then(|chain| chain.get(&block_id).cloned())
+    }
+
+    /// The highest block id this reader has finalized for `zone`, or `None` if it
+    /// has read nothing yet. Used to tell forgery (we have read past the
+    /// referenced block and it is absent) from lag (we simply have not caught up).
+    async fn highest_seen(&self, zone: ZoneId) -> Option<u64> {
+        self.chains
+            .read()
+            .await
+            .get(&zone)
+            .and_then(|chain| chain.keys().copied().max())
+    }
+}
+
+/// The indexer-side Option B verifier.
+///
+/// For every cross-zone dispatch in a block it re-derives the transaction from
+/// the peer's finalized block and rejects it if the bytes differ (a forgery) or
+/// the message was already delivered (a replay), so delivery no longer relies on
+/// trusting the sequencer.
+#[derive(Clone)]
+pub struct CrossZoneVerifier {
+    self_zone: ZoneId,
+    /// Pinned block-signing key per peer zone, enforced during re-derivation.
+    peer_pubkeys: HashMap<ZoneId, PublicKey>,
+    peers: PeerBlocks,
+    seen: Arc<RwLock<HashSet<MessageKey>>>,
+}
+
+impl CrossZoneVerifier {
+    /// Builds the verifier and spawns one peer reader per configured peer.
+    /// Returns `None` when cross-zone messaging is disabled.
+    pub fn start(config: &IndexerConfig) -> Option<Self> {
+        let cross_zone = config.cross_zone.as_ref()?;
+        let self_zone: ZoneId = *config.channel_id.as_ref();
+        let peers = PeerBlocks::default();
+        let mut peer_pubkeys = HashMap::new();
+
+        for peer in &cross_zone.peers {
+            let node = NodeHttpClient::new(
+                CommonHttpClient::new(config.bedrock_config.auth.clone().map(Into::into)),
+                config.bedrock_config.addr.clone(),
+            );
+            if let Some(bytes) = peer.expected_block_signing_pubkey {
+                let pubkey = PublicKey::try_new(bytes)
+                    .expect("configured peer block-signing pubkey is a valid key");
+                peer_pubkeys.insert(peer.channel_id, pubkey);
+            }
+            tokio::spawn(read_peer(
+                ZoneIndexer::new(ChannelId::from(peer.channel_id), node),
+                peer.channel_id,
+                peers.clone(),
+                config.consensus_info_polling_interval,
+            ));
+        }
+
+        Some(Self {
+            self_zone,
+            peer_pubkeys,
+            peers,
+            seen: Arc::new(RwLock::new(HashSet::new())),
+        })
+    }
+
+    /// Verifies every cross-zone dispatch in a block, returning `Err` on the
+    /// first forged or replayed dispatch. The caller halts ingestion on error.
+    pub async fn verify_block(&self, block: &Block) -> Result<()> {
+        for tx in &block.body.transactions {
+            let Some(msg) = Self::decode_dispatch(tx) else {
+                continue;
+            };
+
+            let key = message_key(&msg.src_zone, msg.src_block_id, msg.src_tx_index);
+            if self.seen.read().await.contains(&key) {
+                bail!(
+                    "cross-zone replay: message {} re-delivered",
+                    hex::encode(key)
+                );
+            }
+
+            let expected = self.rederive(&msg).await?;
+            if LeeTransaction::Public(expected) != *tx {
+                bail!(
+                    "forged cross-zone dispatch from zone {} block {} tx {}: re-derivation mismatch",
+                    hex::encode(msg.src_zone),
+                    msg.src_block_id,
+                    msg.src_tx_index
+                );
+            }
+
+            self.seen.write().await.insert(key);
+            info!(
+                "Verified cross-zone dispatch from zone {} block {} tx {}",
+                hex::encode(msg.src_zone),
+                msg.src_block_id,
+                msg.src_tx_index
+            );
+        }
+        Ok(())
+    }
+
+    /// Decodes a transaction into the cross-zone message it dispatches, or `None`
+    /// if it is not an inbox dispatch.
+    fn decode_dispatch(tx: &LeeTransaction) -> Option<CrossZoneMessage> {
+        let LeeTransaction::Public(public_tx) = tx else {
+            return None;
+        };
+        if public_tx.message().program_id != programs::cross_zone_inbox().id() {
+            return None;
+        }
+        match risc0_zkvm::serde::from_slice::<InboxInstruction, _>(
+            &public_tx.message().instruction_data,
+        ) {
+            Ok(InboxInstruction::Dispatch(msg)) => Some(msg),
+            Err(_) => None,
+        }
+    }
+
+    /// Re-derives the dispatch transaction the watcher should have injected for
+    /// `msg`, reading the source emission from the peer's finalized block.
+    async fn rederive(&self, msg: &CrossZoneMessage) -> Result<lee::PublicTransaction> {
+        let peer_block = self
+            .wait_for_peer_block(msg.src_zone, msg.src_block_id)
+            .await?;
+
+        // Equivocation defense: the source block must be signed by the peer's
+        // pinned block-signing key, not merely inscribed on the channel.
+        if let Some(expected) = self.peer_pubkeys.get(&msg.src_zone)
+            && !peer_block.is_signed_by(expected)
+        {
+            bail!(
+                "forged cross-zone dispatch: peer zone {} block {} is not signed by the pinned block-signing key",
+                hex::encode(msg.src_zone),
+                msg.src_block_id
+            );
+        }
+
+        let emission_tx = peer_block
+            .body
+            .transactions
+            .get(usize::try_from(msg.src_tx_index).expect("u32 index fits in usize"))
+            .ok_or_else(|| {
+                anyhow::anyhow!(
+                    "src_tx_index {} out of range in peer block",
+                    msg.src_tx_index
+                )
+            })?;
+
+        let LeeTransaction::Public(emission_tx) = emission_tx else {
+            bail!("peer emission transaction is not public");
+        };
+        let message = emission_tx.message();
+        let emission =
+            extract_emission(message.program_id, &message.instruction_data).ok_or_else(|| {
+                anyhow::anyhow!("peer transaction at src_tx_index is not a recognized emitter")
+            })?;
+
+        if emission.target_zone != self.self_zone {
+            bail!("peer emission targets a different zone");
+        }
+
+        Ok(build_dispatch_from_emission(
+            msg.src_zone,
+            msg.src_block_id,
+            msg.src_tx_index,
+            message.program_id,
+            emission.target_program_id,
+            &emission.target_accounts,
+            emission.payload,
+        ))
+    }
+
+    /// Resolves the referenced peer block, distinguishing forgery from lag.
+    ///
+    /// If the block is cached, return it. If our peer reader has already
+    /// finalized past `block_id` and we still do not have it, the reference is to
+    /// a block that does not exist on the peer chain, a forgery, so reject now.
+    /// Otherwise the reader simply has not caught up yet: keep waiting, since a
+    /// legitimate dispatch is only injected after its peer block finalized and
+    /// our reader of the same finalized chain will see it too. Rejecting on a
+    /// timeout here would turn a lagging reader into a permanent halt of an
+    /// honest message.
+    async fn wait_for_peer_block(&self, zone: ZoneId, block_id: u64) -> Result<Block> {
+        let mut waited = Duration::ZERO;
+        loop {
+            if let Some(block) = self.peers.get(zone, block_id).await {
+                return Ok(block);
+            }
+            if self
+                .peers
+                .highest_seen(zone)
+                .await
+                .is_some_and(|h| h >= block_id)
+            {
+                bail!(
+                    "forged cross-zone reference: peer zone {} finalized past block {} but it is absent",
+                    hex::encode(zone),
+                    block_id
+                );
+            }
+            if !waited.is_zero() && waited.as_secs().is_multiple_of(LAG_LOG_INTERVAL.as_secs()) {
+                info!(
+                    "Waiting for peer zone {} to finalize block {} ({}s); reader is behind",
+                    hex::encode(zone),
+                    block_id,
+                    waited.as_secs()
+                );
+            }
+            tokio::time::sleep(Duration::from_secs(1)).await;
+            waited = waited.saturating_add(Duration::from_secs(1));
+        }
+    }
+}
+
+/// Reads a peer zone's finalized blocks from Bedrock into the shared cache.
+#[expect(
+    clippy::infinite_loop,
+    reason = "the peer reader runs for the lifetime of the indexer process"
+)]
+async fn read_peer(
+    zone_indexer: ZoneIndexer<NodeHttpClient>,
+    peer_zone: ZoneId,
+    peers: PeerBlocks,
+    poll_interval: Duration,
+) {
+    info!(
+        "Cross-zone peer reader started for {}",
+        hex::encode(peer_zone)
+    );
+
+    let mut cursor = None;
+    loop {
+        let stream = match zone_indexer.next_messages(cursor).await {
+            Ok(stream) => stream,
+            Err(err) => {
+                error!(
+                    "Peer reader next_messages failed for {}: {err}",
+                    hex::encode(peer_zone)
+                );
+                tokio::time::sleep(poll_interval).await;
+                continue;
+            }
+        };
+        let mut stream = std::pin::pin!(stream);
+
+        while let Some((msg, slot)) = stream.next().await {
+            if let ZoneMessage::Block(zone_block) = msg {
+                match borsh::from_slice::<Block>(&zone_block.data) {
+                    Ok(block) => peers.insert(peer_zone, block).await,
+                    Err(err) => error!("Peer reader failed to deserialize block: {err}"),
+                }
+            }
+            cursor = Some(slot);
+        }
+
+        tokio::time::sleep(poll_interval).await;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use common::test_utils::produce_dummy_block;
+    use lee::{
+        PrivateKey, PublicKey, PublicTransaction,
+        public_transaction::{Message, WitnessSet},
+    };
+    use ping_core::{SenderInstruction, ping_record_pda};
+
+    use super::*;
+
+    const SELF_ZONE: ZoneId = [1; 32];
+    const PEER_ZONE: ZoneId = [2; 32];
+    const PEER_BLOCK_ID: u64 = 5;
+
+    fn verifier() -> CrossZoneVerifier {
+        verifier_with_pinned_keys(HashMap::new())
+    }
+
+    fn verifier_with_pinned_keys(peer_pubkeys: HashMap<ZoneId, PublicKey>) -> CrossZoneVerifier {
+        CrossZoneVerifier {
+            self_zone: SELF_ZONE,
+            peer_pubkeys,
+            peers: PeerBlocks::default(),
+            seen: Arc::new(RwLock::new(HashSet::new())),
+        }
+    }
+
+    /// A `ping_sender` emission addressed to `SELF_ZONE` carrying `payload`.
+    fn emission(payload: &[u8]) -> LeeTransaction {
+        let receiver_id = programs::ping_receiver().id();
+        let send = SenderInstruction::Send {
+            outbox_program_id: programs::cross_zone_outbox().id(),
+            target_zone: SELF_ZONE,
+            target_program_id: receiver_id,
+            target_accounts: vec![ping_record_pda(receiver_id).into_value()],
+            payload: payload.to_vec(),
+            ordinal: 0,
+        };
+        let message = Message::try_new(programs::ping_sender().id(), vec![], vec![], send)
+            .expect("emission serializes");
+        LeeTransaction::Public(PublicTransaction::new(
+            message,
+            WitnessSet::from_raw_parts(vec![]),
+        ))
+    }
+
+    /// The dispatch a watcher would inject for a `PEER_BLOCK_ID` emission of `payload`.
+    fn dispatch(payload: &[u8]) -> LeeTransaction {
+        let receiver_id = programs::ping_receiver().id();
+        LeeTransaction::Public(build_dispatch_from_emission(
+            PEER_ZONE,
+            PEER_BLOCK_ID,
+            0,
+            programs::ping_sender().id(),
+            receiver_id,
+            &[ping_record_pda(receiver_id).into_value()],
+            payload.to_vec(),
+        ))
+    }
+
+    #[tokio::test]
+    async fn verifies_dispatch_matching_a_peer_emission() {
+        let verifier = verifier();
+        verifier
+            .peers
+            .insert(
+                PEER_ZONE,
+                produce_dummy_block(PEER_BLOCK_ID, None, vec![emission(b"hi")]),
+            )
+            .await;
+
+        let block = produce_dummy_block(9, None, vec![dispatch(b"hi")]);
+        verifier
+            .verify_block(&block)
+            .await
+            .expect("dispatch matching the peer emission verifies");
+    }
+
+    #[tokio::test]
+    async fn rejects_dispatch_with_no_matching_emission() {
+        let verifier = verifier();
+        // The peer block carries the real emission, but the block claims a
+        // different payload, so re-derivation does not reproduce it.
+        verifier
+            .peers
+            .insert(
+                PEER_ZONE,
+                produce_dummy_block(PEER_BLOCK_ID, None, vec![emission(b"real")]),
+            )
+            .await;
+
+        let block = produce_dummy_block(9, None, vec![dispatch(b"forged")]);
+        let err = verifier.verify_block(&block).await.unwrap_err();
+        assert!(
+            err.to_string().contains("forged"),
+            "unexpected error: {err}"
+        );
+    }
+
+    #[tokio::test]
+    async fn verifies_dispatch_signed_by_the_pinned_peer_key() {
+        // produce_dummy_block signs with PrivateKey([37; 32]); pin its pubkey.
+        let signer = PublicKey::new_from_private_key(&PrivateKey::try_new([37; 32]).unwrap());
+        let mut keys = HashMap::new();
+        keys.insert(PEER_ZONE, signer);
+        let verifier = verifier_with_pinned_keys(keys);
+        verifier
+            .peers
+            .insert(
+                PEER_ZONE,
+                produce_dummy_block(PEER_BLOCK_ID, None, vec![emission(b"hi")]),
+            )
+            .await;
+
+        let block = produce_dummy_block(9, None, vec![dispatch(b"hi")]);
+        verifier
+            .verify_block(&block)
+            .await
+            .expect("a dispatch from the pinned signer verifies");
+    }
+
+    #[tokio::test]
+    async fn rejects_dispatch_from_a_block_not_signed_by_the_pinned_key() {
+        // Pin a different key than the one that signed the peer block.
+        let mut keys = HashMap::new();
+        keys.insert(PEER_ZONE, PublicKey::try_new([42; 32]).unwrap());
+        let verifier = verifier_with_pinned_keys(keys);
+        verifier
+            .peers
+            .insert(
+                PEER_ZONE,
+                produce_dummy_block(PEER_BLOCK_ID, None, vec![emission(b"hi")]),
+            )
+            .await;
+
+        let block = produce_dummy_block(9, None, vec![dispatch(b"hi")]);
+        let err = verifier.verify_block(&block).await.unwrap_err();
+        assert!(
+            err.to_string().contains("pinned"),
+            "unexpected error: {err}"
+        );
+    }
+
+    #[tokio::test]
+    async fn rejects_reference_to_a_block_the_peer_never_finalized() {
+        let verifier = verifier();
+        // The reader has finalized past PEER_BLOCK_ID (it holds a later block) but
+        // never saw PEER_BLOCK_ID itself, so a dispatch referencing it is a forgery
+        // and must be rejected rather than waited on forever.
+        verifier
+            .peers
+            .insert(
+                PEER_ZONE,
+                produce_dummy_block(PEER_BLOCK_ID + 1, None, vec![emission(b"hi")]),
+            )
+            .await;
+
+        let block = produce_dummy_block(9, None, vec![dispatch(b"hi")]);
+        let err = verifier.verify_block(&block).await.unwrap_err();
+        assert!(
+            err.to_string().contains("forged"),
+            "unexpected error: {err}"
+        );
+    }
+
+    #[tokio::test]
+    async fn rejects_replayed_dispatch() {
+        let verifier = verifier();
+        verifier
+            .peers
+            .insert(
+                PEER_ZONE,
+                produce_dummy_block(PEER_BLOCK_ID, None, vec![emission(b"hi")]),
+            )
+            .await;
+
+        let first = produce_dummy_block(9, None, vec![dispatch(b"hi")]);
+        verifier
+            .verify_block(&first)
+            .await
+            .expect("first delivery verifies");
+
+        let replay = produce_dummy_block(10, None, vec![dispatch(b"hi")]);
+        let err = verifier.verify_block(&replay).await.unwrap_err();
+        assert!(
+            err.to_string().contains("replay"),
+            "unexpected error: {err}"
+        );
+    }
+}

lez/indexer/core/src/lib.rs

@@ -17,11 +17,13 @@ use crate::{
     block_store::{AcceptOutcome, IndexerStore},
     chain_consistency::ChainConsistency,
     config::IndexerConfig,
+    cross_zone_verifier::CrossZoneVerifier,
     status::{IndexerStatus, IndexerSyncStatus},
 };
 pub mod block_store;
 pub mod chain_consistency;
 pub mod config;
+pub mod cross_zone_verifier;
 pub mod ingest_error;
 mod retry;
 pub mod stall_reason;
@@ -39,6 +41,8 @@ pub struct IndexerCore {
     pub store: IndexerStore,
     /// Live ingestion status; updated by the ingest stream, read by `status`.
     pub status: Arc<ArcSwap<IndexerSyncStatus>>,
+    /// Option B cross-zone verifier; `None` when cross-zone messaging is disabled.
+    pub verifier: Option<CrossZoneVerifier>,
 }
 
 impl IndexerCore {
@@ -89,12 +93,35 @@ impl IndexerCore {
         );
         let zone_indexer = ZoneIndexer::new(config.channel_id, node.clone());
 
+        // Genesis accounts the indexer must seed to match the sequencer's state,
+        // since none are produced by a transaction: the cross-zone inbox config
+        // and any bridge-lock holdings. Both go through the same builders the
+        // sequencer uses, so the states are byte-identical.
+        let mut genesis_seed = Vec::new();
+        if let Some(cross_zone) = config.cross_zone.as_ref() {
+            let self_zone: [u8; 32] = *config.channel_id.as_ref();
+            genesis_seed.push(cross_zone::build_inbox_config_account(
+                self_zone, cross_zone,
+            ));
+        }
+        for holding in &config.bridge_lock_holdings {
+            genesis_seed.push(cross_zone::build_holding_account(
+                holding.holder,
+                holding.amount,
+            ));
+        }
+
+        // Option B verifier: re-derives each cross-zone dispatch from the peer's
+        // finalized blocks. `None` when cross-zone messaging is disabled.
+        let verifier = CrossZoneVerifier::start(&config);
+
         Ok(Self {
             zone_indexer: Arc::new(zone_indexer),
+            store: IndexerStore::open_db(&home, genesis_seed)?,
             node,
             config,
-            store: IndexerStore::open_db(&home)?,
             status: Arc::new(ArcSwap::from_pointee(IndexerSyncStatus::starting())),
+            verifier,
         })
     }
 
@@ -229,6 +256,22 @@ impl IndexerCore {
                         }
                     };
 
+                    // Option B: re-derive and verify every cross-zone dispatch
+                    // before applying the block. A forged or replayed dispatch
+                    // halts ingestion rather than persisting an invalid state.
+                    if let Some(verifier) = &self.verifier
+                        && let Err(err) = verifier.verify_block(&block).await
+                    {
+                        error!(
+                            "Cross-zone verification failed for block {}: {err:#}. Halting indexer ingestion.",
+                            block.header.block_id
+                        );
+                        self.set_status(IndexerSyncStatus::error(format!(
+                            "cross-zone verification failed: {err:#}"
+                        )));
+                        return;
+                    }
+
                     match self.store.accept_block(&block, slot).await {
                         Ok(AcceptOutcome::Applied) => {
                             retry_gate.reset();

lez/programs/Cargo.toml

@@ -54,6 +54,36 @@ name = "vault"
 path = "vault/src/main.rs"
 required-features = ["programs"]
 
+[[bin]]
+name = "cross_zone_outbox"
+path = "cross_zone_outbox/src/main.rs"
+required-features = ["programs"]
+
+[[bin]]
+name = "cross_zone_inbox"
+path = "cross_zone_inbox/src/main.rs"
+required-features = ["programs"]
+
+[[bin]]
+name = "ping_sender"
+path = "ping_sender/src/main.rs"
+required-features = ["programs"]
+
+[[bin]]
+name = "ping_receiver"
+path = "ping_receiver/src/main.rs"
+required-features = ["programs"]
+
+[[bin]]
+name = "bridge_lock"
+path = "bridge_lock/src/main.rs"
+required-features = ["programs"]
+
+[[bin]]
+name = "wrapped_token"
+path = "wrapped_token/src/main.rs"
+required-features = ["programs"]
+
 [features]
 # TODO: Uncomment once https://github.com/risc0/risc0/issues/3772 is resolved.
 # default = ["artifacts"]
@@ -78,6 +108,11 @@ programs = [
   "dep:faucet_core",
   "dep:token_core",
   "dep:vault_core",
+  "dep:cross_zone_inbox_core",
+  "dep:cross_zone_outbox_core",
+  "dep:bridge_lock_core",
+  "dep:wrapped_token_core",
+  "dep:ping_core",
 ]
 
 [dependencies]
@@ -92,6 +127,11 @@ clock_core = { workspace = true, optional = true }
 faucet_core = { workspace = true, optional = true }
 token_core = { workspace = true, optional = true }
 vault_core = { workspace = true, optional = true }
+cross_zone_inbox_core = { workspace = true, optional = true }
+cross_zone_outbox_core = { workspace = true, optional = true }
+bridge_lock_core = { workspace = true, optional = true }
+wrapped_token_core = { workspace = true, optional = true }
+ping_core = { workspace = true, optional = true }
 
 amm_program = { path = "amm", optional = true }
 associated_token_account_program = { path = "associated_token_account", optional = true }

lez/programs/bridge_lock/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "bridge_lock_program"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+bridge_lock_core.workspace = true
+cross_zone_outbox_core.workspace = true
+wrapped_token_core.workspace = true
+risc0-zkvm.workspace = true

lez/programs/bridge_lock/core/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "bridge_lock_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }

lez/programs/bridge_lock/core/src/lib.rs

@@ -0,0 +1,71 @@
+//! Core types for the bridge-lock program, the source side of the cross-zone
+//! token bridge. A holder locks part of their balance into an escrow and emits a
+//! cross-zone message minting the wrapped token on the target zone.
+
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const ESCROW_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/BridgeLockEscrow/0000/";
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Lock `amount` of the holder's balance and emit a cross-zone message
+    /// minting the wrapped token on `target_zone`. The emission fields mirror
+    /// `cross_zone_outbox::Instruction::Emit` so the watcher reads them directly.
+    ///
+    /// Required accounts (3): holder holding (authorized), escrow PDA, outbox PDA.
+    Lock {
+        amount: u128,
+        target_zone: [u8; 32],
+        target_program_id: ProgramId,
+        target_accounts: Vec<[u8; 32]>,
+        payload: Vec<u8>,
+        outbox_program_id: ProgramId,
+        ordinal: u32,
+    },
+}
+
+/// PDA accumulating all locked balance on this zone.
+#[must_use]
+pub fn escrow_account_id(bridge_lock_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&bridge_lock_id, &escrow_seed())
+}
+
+#[must_use]
+pub const fn escrow_seed() -> PdaSeed {
+    PdaSeed::new(ESCROW_SEED_DOMAIN)
+}
+
+/// Reads a bridgeable balance from account data; empty data is a zero balance.
+#[must_use]
+pub fn read_balance(data: &[u8]) -> u128 {
+    if data.len() < 16 {
+        return 0;
+    }
+    u128::from_le_bytes(data[..16].try_into().unwrap_or_else(|_| unreachable!()))
+}
+
+#[must_use]
+pub const fn balance_bytes(amount: u128) -> [u8; 16] {
+    amount.to_le_bytes()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn balance_round_trips() {
+        assert_eq!(read_balance(&balance_bytes(7)), 7);
+        assert_eq!(read_balance(&[]), 0);
+    }
+
+    #[test]
+    fn escrow_is_stable() {
+        let id: ProgramId = [4; 8];
+        assert_eq!(escrow_account_id(id), escrow_account_id(id));
+    }
+}

lez/programs/bridge_lock/src/main.rs

@@ -0,0 +1,121 @@
+use bridge_lock_core::{Instruction, balance_bytes, escrow_account_id, escrow_seed, read_balance};
+use cross_zone_outbox_core::Instruction as OutboxInstruction;
+use lee_core::{
+    account::AccountWithMetadata,
+    program::{AccountPostState, ChainedCall, Claim, ProgramInput, ProgramOutput, read_lee_inputs},
+};
+use wrapped_token_core::Instruction as WrappedInstruction;
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id,
+            pre_states,
+            instruction,
+        },
+        instruction_words,
+    ) = read_lee_inputs::<Instruction>();
+
+    assert!(
+        caller_program_id.is_none(),
+        "bridge_lock is only invoked as a top-level user transaction"
+    );
+
+    let Instruction::Lock {
+        amount,
+        target_zone,
+        target_program_id,
+        target_accounts,
+        payload,
+        outbox_program_id,
+        ordinal,
+    } = instruction;
+
+    // Value conservation: the forwarded payload must mint exactly what is locked.
+    let WrappedInstruction::Mint {
+        amount: mint_amount,
+        ..
+    } = decode_mint(&payload);
+    assert_eq!(
+        mint_amount, amount,
+        "locked amount must equal the wrapped mint amount"
+    );
+
+    // pre_states: [holder holding (authorized), escrow PDA, outbox PDA].
+    let [holder, escrow, outbox] = <[AccountWithMetadata; 3]>::try_from(pre_states)
+        .expect("Lock requires holder, escrow, and outbox accounts");
+
+    assert!(holder.is_authorized, "holder must authorize the lock");
+    assert_eq!(
+        holder.account.program_owner, self_program_id,
+        "holder account must be a bridge_lock holding"
+    );
+    assert_eq!(
+        escrow.account_id,
+        escrow_account_id(self_program_id),
+        "second account must be the escrow PDA"
+    );
+
+    let holder_new = read_balance(&holder.account.data.clone().into_inner())
+        .checked_sub(amount)
+        .expect("insufficient balance to lock");
+    let escrow_new = read_balance(&escrow.account.data.clone().into_inner())
+        .checked_add(amount)
+        .expect("escrow balance overflow");
+
+    let mut holder_account = holder.account.clone();
+    holder_account.data = balance_bytes(holder_new)
+        .to_vec()
+        .try_into()
+        .expect("balance fits in account data");
+    let holder_post = AccountPostState::new(holder_account);
+
+    let mut escrow_account = escrow.account.clone();
+    escrow_account.data = balance_bytes(escrow_new)
+        .to_vec()
+        .try_into()
+        .expect("balance fits in account data");
+    let escrow_post =
+        AccountPostState::new_claimed_if_default(escrow_account, Claim::Pda(escrow_seed()));
+
+    let call = ChainedCall::new(
+        outbox_program_id,
+        vec![outbox.clone()],
+        &OutboxInstruction::Emit {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ordinal,
+        },
+    );
+
+    ProgramOutput::new(
+        self_program_id,
+        caller_program_id,
+        instruction_words,
+        vec![holder, escrow, outbox.clone()],
+        vec![
+            holder_post,
+            escrow_post,
+            AccountPostState::new(outbox.account),
+        ],
+    )
+    .with_chained_calls(vec![call])
+    .write();
+}
+
+/// Decodes the cross-zone payload (risc0 words, little-endian bytes) into the
+/// wrapped-token instruction it carries.
+fn decode_mint(payload: &[u8]) -> WrappedInstruction {
+    assert!(
+        payload.len().is_multiple_of(4),
+        "payload must be u32-aligned instruction words"
+    );
+    let words: Vec<u32> = payload
+        .chunks_exact(4)
+        .map(|chunk| u32::from_le_bytes(chunk.try_into().unwrap_or_else(|_| unreachable!())))
+        .collect();
+    risc0_zkvm::serde::from_slice(&words).expect("payload decodes to a wrapped-token instruction")
+}

lez/programs/cross_zone_inbox/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "cross_zone_inbox_program"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+cross_zone_inbox_core.workspace = true

lez/programs/cross_zone_inbox/core/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "cross_zone_inbox_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+risc0-zkvm.workspace = true
+borsh.workspace = true

lez/programs/cross_zone_inbox/core/src/lib.rs

@@ -0,0 +1,203 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+use borsh::{BorshDeserialize, BorshSerialize};
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+/// Source blocks per seen-set shard, so no single seen account grows without bound.
+pub const EPOCH_BLOCKS: u64 = 10_000;
+
+const MESSAGE_KEY_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/CrossZoneMsgKey/00000/";
+const INBOX_CONFIG_SEED: [u8; 32] = *b"/LEZ/v0.3/CrossZoneInboxCfg/000/";
+const INBOX_SEEN_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/CrossZoneInboxSeen/00/";
+
+/// Raw 32-byte zone (channel) id; the host maps it to the zone-sdk `ChannelId`.
+pub type ZoneId = [u8; 32];
+
+/// Block-signing public key pinned per peer zone.
+pub type ExpectedPubkey = [u8; 32];
+
+/// Content-addressed replay key for a delivered message.
+pub type MessageKey = [u8; 32];
+
+/// A peer zone whose outbox a zone watches for inbound cross-zone messages.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct CrossZonePeer {
+    /// The peer's Bedrock channel; its 32 bytes double as the peer's zone id.
+    pub channel_id: ZoneId,
+    /// Programs on the local zone a message from this peer is allowed to target.
+    pub allowed_targets: Vec<ProgramId>,
+    /// The peer's block-signing public key, pinned to reject blocks inscribed by
+    /// anyone other than that zone's sequencer. `None` skips the check (the
+    /// channel signer is still authenticated by the zone-sdk).
+    #[serde(default)]
+    pub expected_block_signing_pubkey: Option<[u8; 32]>,
+}
+
+/// Cross-zone configuration shared by a zone's sequencer (watcher) and indexer
+/// (verifier): the peers it reads from Bedrock and, per peer, the local programs
+/// they may deliver to.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct CrossZoneConfig {
+    pub peers: Vec<CrossZonePeer>,
+}
+
+/// A finalized outbound message observed on a peer zone, addressed to a program
+/// on this zone. The watcher fills it from the peer's block; it is never
+/// self-reported by a user.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct CrossZoneMessage {
+    pub src_zone: ZoneId,
+    pub src_block_id: u64,
+    pub src_tx_index: u32,
+    pub src_program_id: ProgramId,
+    pub target_program_id: ProgramId,
+    pub payload: Vec<u8>,
+    /// Reserved for a future source-state proof; MUST be `None` in v1.
+    pub l1_inclusion_witness: Option<Vec<u8>>,
+}
+
+/// Peer and per-peer target allowlists, plus this inbox's own zone id.
+#[derive(
+    Clone, Debug, Default, PartialEq, Eq, Serialize, Deserialize, BorshSerialize, BorshDeserialize,
+)]
+pub struct InboxConfig {
+    pub self_zone: ZoneId,
+    pub allowed_peers: BTreeMap<ZoneId, ExpectedPubkey>,
+    pub allowed_targets: BTreeMap<ZoneId, Vec<ProgramId>>,
+}
+
+impl InboxConfig {
+    /// Borsh-encoded form stored in the inbox config account.
+    #[must_use]
+    pub fn to_bytes(&self) -> Vec<u8> {
+        borsh::to_vec(self).expect("InboxConfig serializes")
+    }
+
+    /// Decodes an [`InboxConfig`] from account data.
+    pub fn from_bytes(bytes: &[u8]) -> borsh::io::Result<Self> {
+        borsh::from_slice(bytes)
+    }
+}
+
+/// The replay keys seen for one `(src_zone, epoch)` shard.
+#[derive(Clone, Debug, Default, PartialEq, Eq, BorshSerialize, BorshDeserialize)]
+pub struct SeenShard(pub BTreeSet<MessageKey>);
+
+impl SeenShard {
+    /// Decodes a shard from account data; empty data is an empty shard.
+    pub fn from_bytes(bytes: &[u8]) -> borsh::io::Result<Self> {
+        if bytes.is_empty() {
+            return Ok(Self::default());
+        }
+        borsh::from_slice(bytes)
+    }
+
+    #[must_use]
+    pub fn to_bytes(&self) -> Vec<u8> {
+        borsh::to_vec(self).expect("SeenShard serializes")
+    }
+
+    #[must_use]
+    pub fn contains(&self, key: &MessageKey) -> bool {
+        self.0.contains(key)
+    }
+
+    /// Inserts a key; returns true if it was newly inserted.
+    pub fn insert(&mut self, key: MessageKey) -> bool {
+        self.0.insert(key)
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Delivers a finalized peer message to its target program.
+    Dispatch(CrossZoneMessage),
+}
+
+/// Content-addressed replay key for a delivered message.
+///
+/// Hashes `(src_zone, src_block_id, src_tx_index)` under a domain separator.
+/// Watcher-independent and immune to proof malleability, since it keys on block
+/// id plus index rather than a tx hash.
+#[must_use]
+pub fn message_key(src_zone: &ZoneId, src_block_id: u64, src_tx_index: u32) -> MessageKey {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let mut bytes = [0_u8; 76];
+    bytes[..32].copy_from_slice(&MESSAGE_KEY_DOMAIN);
+    bytes[32..64].copy_from_slice(src_zone);
+    bytes[64..72].copy_from_slice(&src_block_id.to_le_bytes());
+    bytes[72..].copy_from_slice(&src_tx_index.to_le_bytes());
+
+    Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!())
+}
+
+/// The config account holding the allowlists.
+#[must_use]
+pub fn inbox_config_account_id(inbox_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&inbox_id, &PdaSeed::new(INBOX_CONFIG_SEED))
+}
+
+/// The seen-set shard for the `(src_zone, epoch)` the message falls in.
+#[must_use]
+pub fn inbox_seen_shard_account_id(
+    inbox_id: ProgramId,
+    src_zone: &ZoneId,
+    src_block_id: u64,
+) -> AccountId {
+    AccountId::for_public_pda(&inbox_id, &inbox_seen_shard_seed(src_zone, src_block_id))
+}
+
+/// Seed of the seen-shard PDA, exposed so the guest can claim the account.
+#[must_use]
+pub fn inbox_seen_shard_seed(src_zone: &ZoneId, src_block_id: u64) -> PdaSeed {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let src_epoch = src_block_id.wrapping_div(EPOCH_BLOCKS);
+    let mut bytes = [0_u8; 72];
+    bytes[..32].copy_from_slice(&INBOX_SEEN_SEED_DOMAIN);
+    bytes[32..64].copy_from_slice(src_zone);
+    bytes[64..].copy_from_slice(&src_epoch.to_le_bytes());
+
+    let seed: [u8; 32] = Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    PdaSeed::new(seed)
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn zone(b: u8) -> ZoneId {
+        [b; 32]
+    }
+
+    #[test]
+    fn message_key_is_stable_and_content_addressed() {
+        assert_eq!(message_key(&zone(1), 7, 3), message_key(&zone(1), 7, 3));
+        assert_ne!(message_key(&zone(1), 7, 3), message_key(&zone(2), 7, 3));
+        assert_ne!(message_key(&zone(1), 7, 3), message_key(&zone(1), 8, 3));
+        assert_ne!(message_key(&zone(1), 7, 3), message_key(&zone(1), 7, 4));
+    }
+
+    #[test]
+    fn seen_shards_split_on_epoch_boundary() {
+        let id: ProgramId = [9; 8];
+        assert_eq!(
+            inbox_seen_shard_account_id(id, &zone(1), 0),
+            inbox_seen_shard_account_id(id, &zone(1), EPOCH_BLOCKS - 1),
+        );
+        assert_ne!(
+            inbox_seen_shard_account_id(id, &zone(1), EPOCH_BLOCKS - 1),
+            inbox_seen_shard_account_id(id, &zone(1), EPOCH_BLOCKS),
+        );
+    }
+}

lez/programs/cross_zone_inbox/src/main.rs

@@ -0,0 +1,125 @@
+use cross_zone_inbox_core::{
+    InboxConfig, Instruction, SeenShard, inbox_config_account_id, inbox_seen_shard_account_id,
+    inbox_seen_shard_seed, message_key,
+};
+use lee_core::{
+    account::AccountWithMetadata,
+    program::{AccountPostState, ChainedCall, Claim, ProgramInput, ProgramOutput, read_lee_inputs},
+};
+
+fn unchanged(pre: &AccountWithMetadata) -> AccountPostState {
+    AccountPostState::new(pre.account.clone())
+}
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id,
+            pre_states,
+            instruction,
+        },
+        instruction_words,
+    ) = read_lee_inputs::<Instruction>();
+
+    assert!(
+        caller_program_id.is_none(),
+        "Inbox is only invoked as a top-level sequencer-origin transaction"
+    );
+
+    let Instruction::Dispatch(msg) = instruction;
+
+    assert!(
+        msg.l1_inclusion_witness.is_none(),
+        "l1_inclusion_witness must be None in v1"
+    );
+
+    // pre_states layout: [config, seen_shard, then the target accounts].
+    let mut accounts = pre_states.into_iter();
+    let config = accounts.next().expect("config account required");
+    let seen = accounts.next().expect("seen shard account required");
+    let target_accounts: Vec<AccountWithMetadata> = accounts.collect();
+
+    assert_eq!(
+        config.account_id,
+        inbox_config_account_id(self_program_id),
+        "First account must be the inbox config PDA"
+    );
+    assert_eq!(
+        seen.account_id,
+        inbox_seen_shard_account_id(self_program_id, &msg.src_zone, msg.src_block_id),
+        "Second account must be the seen-shard PDA"
+    );
+
+    let cfg = InboxConfig::from_bytes(&config.account.data.clone().into_inner())
+        .expect("inbox config decodes");
+
+    assert!(
+        msg.src_zone != cfg.self_zone,
+        "Source zone must not be this zone"
+    );
+    let allowed_targets = cfg
+        .allowed_targets
+        .get(&msg.src_zone)
+        .expect("Source zone is not an allowed peer");
+    assert!(
+        allowed_targets.contains(&msg.target_program_id),
+        "Target program is not allowed for this peer"
+    );
+
+    let key = message_key(&msg.src_zone, msg.src_block_id, msg.src_tx_index);
+    let mut shard =
+        SeenShard::from_bytes(&seen.account.data.clone().into_inner()).expect("seen shard decodes");
+    let already_seen = shard.contains(&key);
+
+    // On replay this is a no-op: the seen shard is untouched and no call is made.
+    let (seen_post, chained_calls) = if already_seen {
+        (unchanged(&seen), vec![])
+    } else {
+        shard.insert(key);
+        let mut seen_account = seen.account.clone();
+        seen_account.data = shard
+            .to_bytes()
+            .try_into()
+            .expect("seen shard fits in account data");
+        let seen_post = AccountPostState::new_claimed_if_default(
+            seen_account,
+            Claim::Pda(inbox_seen_shard_seed(&msg.src_zone, msg.src_block_id)),
+        );
+
+        // The payload carries the target instruction as risc0 words, little-endian.
+        assert!(
+            msg.payload.len().is_multiple_of(4),
+            "payload must be u32-aligned instruction words"
+        );
+        let instruction_data = msg
+            .payload
+            .chunks_exact(4)
+            .map(|c| u32::from_le_bytes(c.try_into().unwrap_or_else(|_| unreachable!())))
+            .collect();
+
+        let call = ChainedCall {
+            program_id: msg.target_program_id,
+            pre_states: target_accounts.clone(),
+            instruction_data,
+            pda_seeds: vec![],
+        };
+        (seen_post, vec![call])
+    };
+
+    let mut post_states = vec![unchanged(&config), seen_post];
+    post_states.extend(target_accounts.iter().map(unchanged));
+
+    let mut output_pre_states = vec![config, seen];
+    output_pre_states.extend(target_accounts);
+
+    ProgramOutput::new(
+        self_program_id,
+        caller_program_id,
+        instruction_words,
+        output_pre_states,
+        post_states,
+    )
+    .with_chained_calls(chained_calls)
+    .write();
+}

lez/programs/cross_zone_outbox/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "cross_zone_outbox_program"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+cross_zone_outbox_core.workspace = true

lez/programs/cross_zone_outbox/core/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "cross_zone_outbox_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+risc0-zkvm.workspace = true
+borsh.workspace = true

lez/programs/cross_zone_outbox/core/src/lib.rs

@@ -0,0 +1,93 @@
+use borsh::{BorshDeserialize, BorshSerialize};
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const OUTBOX_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/CrossZoneOutbox/00000/";
+
+/// Raw 32-byte zone (channel) id; the host maps it to the zone-sdk `ChannelId`.
+pub type ZoneId = [u8; 32];
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Records an outbound cross-zone message as a write to a self-owned PDA.
+    ///
+    /// Required accounts (1):
+    /// - Outbox PDA account
+    Emit {
+        target_zone: ZoneId,
+        target_program_id: ProgramId,
+        /// Accounts the destination inbox must hand to the target program's
+        /// chained call. The emitter specifies them; the watcher forwards them
+        /// verbatim so the inbox stays target-agnostic.
+        target_accounts: Vec<[u8; 32]>,
+        payload: Vec<u8>,
+        ordinal: u32,
+    },
+}
+
+/// The message as stored in an outbox PDA. The destination zone's watcher reads
+/// this from the inscribed block; the source coordinates are filled by the
+/// watcher, not stored here.
+#[derive(Clone, Debug, PartialEq, Eq, BorshSerialize, BorshDeserialize)]
+pub struct OutboxRecord {
+    pub target_zone: ZoneId,
+    pub target_program_id: ProgramId,
+    pub target_accounts: Vec<[u8; 32]>,
+    pub payload: Vec<u8>,
+}
+
+impl OutboxRecord {
+    /// Borsh-encoded form stored in the outbox PDA's account data.
+    #[must_use]
+    pub fn to_bytes(&self) -> Vec<u8> {
+        borsh::to_vec(self).expect("OutboxRecord serializes")
+    }
+
+    /// Decodes an [`OutboxRecord`] from account data.
+    pub fn from_bytes(bytes: &[u8]) -> borsh::io::Result<Self> {
+        borsh::from_slice(bytes)
+    }
+}
+
+/// PDA holding one emitted message, keyed by destination zone and a per-zone
+/// ordinal.
+#[must_use]
+pub fn outbox_pda(outbox_id: ProgramId, target_zone: &ZoneId, ordinal: u32) -> AccountId {
+    AccountId::for_public_pda(&outbox_id, &outbox_pda_seed(target_zone, ordinal))
+}
+
+/// Seed of an outbox message PDA, exposed so the guest can claim the account.
+#[must_use]
+pub fn outbox_pda_seed(target_zone: &ZoneId, ordinal: u32) -> PdaSeed {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let mut bytes = [0_u8; 68];
+    bytes[..32].copy_from_slice(&OUTBOX_SEED_DOMAIN);
+    bytes[32..64].copy_from_slice(target_zone);
+    bytes[64..].copy_from_slice(&ordinal.to_le_bytes());
+
+    let seed: [u8; 32] = Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    PdaSeed::new(seed)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn outbox_pda_is_unique_per_zone_and_ordinal() {
+        let id: ProgramId = [3; 8];
+        let zone_a = [1; 32];
+        let zone_b = [2; 32];
+
+        assert_eq!(outbox_pda(id, &zone_a, 0), outbox_pda(id, &zone_a, 0));
+        assert_ne!(outbox_pda(id, &zone_a, 0), outbox_pda(id, &zone_a, 1));
+        assert_ne!(outbox_pda(id, &zone_a, 0), outbox_pda(id, &zone_b, 0));
+    }
+}

lez/programs/cross_zone_outbox/src/main.rs

@@ -0,0 +1,72 @@
+use cross_zone_outbox_core::{Instruction, OutboxRecord, outbox_pda, outbox_pda_seed};
+use lee_core::{
+    account::AccountWithMetadata,
+    program::{AccountPostState, Claim, ProgramInput, ProgramOutput, read_lee_inputs},
+};
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id,
+            pre_states,
+            instruction,
+        },
+        instruction_words,
+    ) = read_lee_inputs::<Instruction>();
+
+    assert!(
+        caller_program_id.is_some(),
+        "Outbox is only callable through a chain call from a user program"
+    );
+
+    let (target_zone, target_program_id, target_accounts, payload, ordinal) = match instruction {
+        Instruction::Emit {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ordinal,
+        } => (
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ordinal,
+        ),
+    };
+
+    let [outbox] =
+        <[AccountWithMetadata; 1]>::try_from(pre_states).expect("Emit requires exactly 1 account");
+
+    assert_eq!(
+        outbox.account_id,
+        outbox_pda(self_program_id, &target_zone, ordinal),
+        "Account must be the outbox PDA for (target_zone, ordinal)"
+    );
+
+    let mut post_account = outbox.account.clone();
+    post_account.data = OutboxRecord {
+        target_zone,
+        target_program_id,
+        target_accounts,
+        payload,
+    }
+    .to_bytes()
+    .try_into()
+    .expect("OutboxRecord fits in account data");
+
+    let post = AccountPostState::new_claimed_if_default(
+        post_account,
+        Claim::Pda(outbox_pda_seed(&target_zone, ordinal)),
+    );
+
+    ProgramOutput::new(
+        self_program_id,
+        caller_program_id,
+        instruction_words,
+        vec![outbox],
+        vec![post],
+    )
+    .write();
+}

lez/programs/ping_core/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "ping_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }

lez/programs/ping_core/src/lib.rs

@@ -0,0 +1,38 @@
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const PING_RECORD_SEED: [u8; 32] = *b"/LEZ/v0.3/PingRecord/0000000000/";
+
+/// Instruction delivered to `ping_receiver` by the inbox: record the payload.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum ReceiverInstruction {
+    Record { payload: Vec<u8> },
+}
+
+/// Instruction to `ping_sender`: forwarded verbatim into `cross_zone_outbox::Instruction::Emit`.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum SenderInstruction {
+    Send {
+        outbox_program_id: ProgramId,
+        target_zone: [u8; 32],
+        target_program_id: ProgramId,
+        target_accounts: Vec<[u8; 32]>,
+        payload: Vec<u8>,
+        ordinal: u32,
+    },
+}
+
+/// The account a `ping_receiver` records the latest delivered payload into.
+#[must_use]
+pub fn ping_record_pda(receiver_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&receiver_id, &ping_record_seed())
+}
+
+/// Seed of the record PDA, exposed so the guest can claim the account.
+#[must_use]
+pub const fn ping_record_seed() -> PdaSeed {
+    PdaSeed::new(PING_RECORD_SEED)
+}

lez/programs/ping_receiver/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "ping_receiver_program"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+ping_core.workspace = true

lez/programs/ping_receiver/src/main.rs

@@ -0,0 +1,48 @@
+use lee_core::{
+    account::AccountWithMetadata,
+    program::{AccountPostState, Claim, ProgramInput, ProgramOutput, read_lee_inputs},
+};
+use ping_core::{ReceiverInstruction, ping_record_pda, ping_record_seed};
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id,
+            pre_states,
+            instruction,
+        },
+        instruction_words,
+    ) = read_lee_inputs::<ReceiverInstruction>();
+
+    assert!(
+        caller_program_id.is_some(),
+        "ping_receiver is only callable through a chained call"
+    );
+
+    let payload = match instruction {
+        ReceiverInstruction::Record { payload } => payload,
+    };
+
+    let [record] = <[AccountWithMetadata; 1]>::try_from(pre_states)
+        .expect("Record requires exactly 1 account");
+    assert_eq!(
+        record.account_id,
+        ping_record_pda(self_program_id),
+        "Account must be the ping record PDA"
+    );
+
+    let mut post_account = record.account.clone();
+    post_account.data = payload.try_into().expect("payload fits in account data");
+    let post =
+        AccountPostState::new_claimed_if_default(post_account, Claim::Pda(ping_record_seed()));
+
+    ProgramOutput::new(
+        self_program_id,
+        caller_program_id,
+        instruction_words,
+        vec![record],
+        vec![post],
+    )
+    .write();
+}

lez/programs/ping_sender/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "ping_sender_program"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+ping_core.workspace = true
+cross_zone_outbox_core.workspace = true

lez/programs/ping_sender/src/main.rs

@@ -0,0 +1,59 @@
+use cross_zone_outbox_core::Instruction as OutboxInstruction;
+use lee_core::{
+    account::AccountWithMetadata,
+    program::{AccountPostState, ChainedCall, ProgramInput, ProgramOutput, read_lee_inputs},
+};
+use ping_core::SenderInstruction;
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id,
+            pre_states,
+            instruction,
+        },
+        instruction_words,
+    ) = read_lee_inputs::<SenderInstruction>();
+
+    assert!(
+        caller_program_id.is_none(),
+        "ping_sender is only invoked as a top-level user transaction"
+    );
+
+    let SenderInstruction::Send {
+        outbox_program_id,
+        target_zone,
+        target_program_id,
+        target_accounts,
+        payload,
+        ordinal,
+    } = instruction;
+
+    // The single account is the outbox PDA the chained call writes into; the
+    // outbox claims it, so ping_sender forwards it unchanged.
+    let [outbox] =
+        <[AccountWithMetadata; 1]>::try_from(pre_states).expect("Send requires exactly 1 account");
+
+    let call = ChainedCall::new(
+        outbox_program_id,
+        vec![outbox.clone()],
+        &OutboxInstruction::Emit {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ordinal,
+        },
+    );
+
+    ProgramOutput::new(
+        self_program_id,
+        caller_program_id,
+        instruction_words,
+        vec![outbox.clone()],
+        vec![AccountPostState::new(outbox.account)],
+    )
+    .with_chained_calls(vec![call])
+    .write();
+}

lez/programs/src/lib.rs

@@ -10,9 +10,12 @@ mod inner {
 
     use guests::{
         AMM_ELF, AMM_ID, ASSOCIATED_TOKEN_ACCOUNT_ELF, ASSOCIATED_TOKEN_ACCOUNT_ID,
-        AUTHENTICATED_TRANSFER_ELF, AUTHENTICATED_TRANSFER_ID, BRIDGE_ELF, BRIDGE_ID, CLOCK_ELF,
-        CLOCK_ID, FAUCET_ELF, FAUCET_ID, PINATA_ELF, PINATA_ID, PINATA_TOKEN_ELF, PINATA_TOKEN_ID,
-        TOKEN_ELF, TOKEN_ID, VAULT_ELF, VAULT_ID,
+        AUTHENTICATED_TRANSFER_ELF, AUTHENTICATED_TRANSFER_ID, BRIDGE_ELF, BRIDGE_ID,
+        BRIDGE_LOCK_ELF, BRIDGE_LOCK_ID, CLOCK_ELF, CLOCK_ID, CROSS_ZONE_INBOX_ELF,
+        CROSS_ZONE_INBOX_ID, CROSS_ZONE_OUTBOX_ELF, CROSS_ZONE_OUTBOX_ID, FAUCET_ELF, FAUCET_ID,
+        PINATA_ELF, PINATA_ID, PINATA_TOKEN_ELF, PINATA_TOKEN_ID, PING_RECEIVER_ELF,
+        PING_RECEIVER_ID, PING_SENDER_ELF, PING_SENDER_ID, TOKEN_ELF, TOKEN_ID, VAULT_ELF,
+        VAULT_ID, WRAPPED_TOKEN_ELF, WRAPPED_TOKEN_ID,
     };
     use lee::program::Program;
 
@@ -87,6 +90,42 @@ mod inner {
         Program::new_unchecked(BRIDGE_ID, Cow::Borrowed(BRIDGE_ELF))
     }
 
+    #[must_use]
+    #[inline]
+    pub const fn cross_zone_outbox() -> Program {
+        Program::new_unchecked(CROSS_ZONE_OUTBOX_ID, Cow::Borrowed(CROSS_ZONE_OUTBOX_ELF))
+    }
+
+    #[must_use]
+    #[inline]
+    pub const fn cross_zone_inbox() -> Program {
+        Program::new_unchecked(CROSS_ZONE_INBOX_ID, Cow::Borrowed(CROSS_ZONE_INBOX_ELF))
+    }
+
+    #[must_use]
+    #[inline]
+    pub const fn ping_sender() -> Program {
+        Program::new_unchecked(PING_SENDER_ID, Cow::Borrowed(PING_SENDER_ELF))
+    }
+
+    #[must_use]
+    #[inline]
+    pub const fn ping_receiver() -> Program {
+        Program::new_unchecked(PING_RECEIVER_ID, Cow::Borrowed(PING_RECEIVER_ELF))
+    }
+
+    #[must_use]
+    #[inline]
+    pub const fn bridge_lock() -> Program {
+        Program::new_unchecked(BRIDGE_LOCK_ID, Cow::Borrowed(BRIDGE_LOCK_ELF))
+    }
+
+    #[must_use]
+    #[inline]
+    pub const fn wrapped_token() -> Program {
+        Program::new_unchecked(WRAPPED_TOKEN_ID, Cow::Borrowed(WRAPPED_TOKEN_ELF))
+    }
+
     #[cfg(test)]
     mod tests {
         use super::*;
@@ -127,6 +166,12 @@ mod inner {
                 (PINATA_TOKEN_ELF, PINATA_TOKEN_ID),
                 (TOKEN_ELF, TOKEN_ID),
                 (VAULT_ELF, VAULT_ID),
+                (CROSS_ZONE_OUTBOX_ELF, CROSS_ZONE_OUTBOX_ID),
+                (CROSS_ZONE_INBOX_ELF, CROSS_ZONE_INBOX_ID),
+                (PING_SENDER_ELF, PING_SENDER_ID),
+                (PING_RECEIVER_ELF, PING_RECEIVER_ID),
+                (BRIDGE_LOCK_ELF, BRIDGE_LOCK_ID),
+                (WRAPPED_TOKEN_ELF, WRAPPED_TOKEN_ID),
             ];
             for (elf, expected_id) in cases {
                 let program = Program::new((*elf).into()).unwrap();

lez/programs/wrapped_token/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "wrapped_token_program"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+wrapped_token_core.workspace = true

lez/programs/wrapped_token/core/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "wrapped_token_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+risc0-zkvm.workspace = true

lez/programs/wrapped_token/core/src/lib.rs

@@ -0,0 +1,121 @@
+//! Core types for the wrapped-token program, the destination side of the
+//! cross-zone bridge. Only the cross-zone inbox may mint; the guest enforces
+//! this by reading the authorized minter from a genesis-seeded config account.
+
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const CONFIG_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/WrappedTokenConfig/00/";
+const HOLDING_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/WrappedTokenHold/00000";
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Credit `amount` wrapped tokens to `recipient`'s holding. Delivered only by
+    /// the cross-zone inbox.
+    ///
+    /// Required accounts (2): the wrapped-token config PDA, then the recipient's
+    /// holding PDA.
+    Mint { recipient: [u8; 32], amount: u128 },
+}
+
+/// PDA holding the authorized minter program id (the cross-zone inbox), seeded at
+/// genesis so the guest can pin its caller without importing the inbox image id.
+#[must_use]
+pub fn config_account_id(wrapped_token_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&wrapped_token_id, &config_seed())
+}
+
+#[must_use]
+pub const fn config_seed() -> PdaSeed {
+    PdaSeed::new(CONFIG_SEED_DOMAIN)
+}
+
+/// PDA holding one recipient's wrapped-token balance.
+#[must_use]
+pub fn holding_account_id(wrapped_token_id: ProgramId, recipient: &[u8; 32]) -> AccountId {
+    AccountId::for_public_pda(&wrapped_token_id, &holding_seed(recipient))
+}
+
+#[must_use]
+pub fn holding_seed(recipient: &[u8; 32]) -> PdaSeed {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let mut bytes = [0_u8; 64];
+    bytes[..32].copy_from_slice(&HOLDING_SEED_DOMAIN);
+    bytes[32..].copy_from_slice(recipient);
+    let seed: [u8; 32] = Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    PdaSeed::new(seed)
+}
+
+/// Encodes the authorized minter program id for the config account's data.
+#[must_use]
+pub fn minter_bytes(minter: ProgramId) -> [u8; 32] {
+    let mut bytes = [0_u8; 32];
+    for (word, chunk) in minter.iter().zip(bytes.chunks_exact_mut(4)) {
+        chunk.copy_from_slice(&word.to_le_bytes());
+    }
+    bytes
+}
+
+/// Decodes the authorized minter program id from the config account's data.
+#[must_use]
+pub fn read_minter(data: &[u8]) -> Option<ProgramId> {
+    if data.len() < 32 {
+        return None;
+    }
+    let mut minter = [0_u32; 8];
+    for (word, chunk) in minter.iter_mut().zip(data[..32].chunks_exact(4)) {
+        *word = u32::from_le_bytes(chunk.try_into().unwrap_or_else(|_| unreachable!()));
+    }
+    Some(minter)
+}
+
+/// Reads a wrapped-token balance from account data; empty data is a zero balance.
+#[must_use]
+pub fn read_balance(data: &[u8]) -> u128 {
+    if data.len() < 16 {
+        return 0;
+    }
+    u128::from_le_bytes(data[..16].try_into().unwrap_or_else(|_| unreachable!()))
+}
+
+#[must_use]
+pub const fn balance_bytes(amount: u128) -> [u8; 16] {
+    amount.to_le_bytes()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn minter_round_trips() {
+        let minter: ProgramId = [1, 2, 3, 4, 5, 6, 7, 8];
+        assert_eq!(read_minter(&minter_bytes(minter)), Some(minter));
+    }
+
+    #[test]
+    fn balance_round_trips() {
+        assert_eq!(read_balance(&balance_bytes(42)), 42);
+        assert_eq!(read_balance(&[]), 0);
+    }
+
+    #[test]
+    fn holding_is_unique_per_recipient() {
+        let id: ProgramId = [9; 8];
+        assert_ne!(
+            holding_account_id(id, &[1; 32]),
+            holding_account_id(id, &[2; 32])
+        );
+        assert_eq!(
+            holding_account_id(id, &[1; 32]),
+            holding_account_id(id, &[1; 32])
+        );
+    }
+}

lez/programs/wrapped_token/src/main.rs

@@ -0,0 +1,70 @@
+use lee_core::{
+    account::AccountWithMetadata,
+    program::{AccountPostState, Claim, ProgramInput, ProgramOutput, read_lee_inputs},
+};
+use wrapped_token_core::{
+    Instruction, balance_bytes, config_account_id, holding_account_id, holding_seed, read_balance,
+    read_minter,
+};
+
+fn main() {
+    let (
+        ProgramInput {
+            self_program_id,
+            caller_program_id,
+            pre_states,
+            instruction,
+        },
+        instruction_words,
+    ) = read_lee_inputs::<Instruction>();
+
+    let Instruction::Mint { recipient, amount } = instruction;
+
+    // pre_states: [config PDA, recipient holding PDA].
+    let [config, holding] = <[AccountWithMetadata; 2]>::try_from(pre_states)
+        .expect("Mint requires the config and recipient holding accounts");
+
+    // The config PDA is genesis-seeded with the authorized minter (the cross-zone
+    // inbox). Pin the caller to it, since the guest cannot import the inbox id.
+    assert_eq!(
+        config.account_id,
+        config_account_id(self_program_id),
+        "first account must be the wrapped-token config PDA"
+    );
+    let minter = read_minter(&config.account.data.clone().into_inner())
+        .expect("config account holds an authorized minter id");
+    assert_eq!(
+        caller_program_id,
+        Some(minter),
+        "Mint is only callable by the authorized minter (the cross-zone inbox)"
+    );
+
+    assert_eq!(
+        holding.account_id,
+        holding_account_id(self_program_id, &recipient),
+        "second account must be the recipient holding PDA"
+    );
+
+    let new_balance = read_balance(&holding.account.data.clone().into_inner())
+        .checked_add(amount)
+        .expect("wrapped-token balance overflow");
+    let mut holding_account = holding.account.clone();
+    holding_account.data = balance_bytes(new_balance)
+        .to_vec()
+        .try_into()
+        .expect("balance fits in account data");
+    let holding_post = AccountPostState::new_claimed_if_default(
+        holding_account,
+        Claim::Pda(holding_seed(&recipient)),
+    );
+    let config_post = AccountPostState::new(config.account.clone());
+
+    ProgramOutput::new(
+        self_program_id,
+        caller_program_id,
+        instruction_words,
+        vec![config, holding],
+        vec![config_post, holding_post],
+    )
+    .write();
+}

lez/sequencer/core/Cargo.toml

@@ -20,6 +20,8 @@ bridge_core.workspace = true
 vault_core.workspace = true
 programs.workspace = true
 system_accounts.workspace = true
+cross_zone.workspace = true
+cross_zone_inbox_core.workspace = true
 
 logos-blockchain-key-management-system-service.workspace = true
 logos-blockchain-core.workspace = true

lez/sequencer/core/src/config.rs

@@ -8,6 +8,7 @@ use std::{
 use anyhow::Result;
 use bytesize::ByteSize;
 use common::config::BasicAuth;
+pub use cross_zone_inbox_core::{CrossZoneConfig, CrossZonePeer};
 use humantime_serde;
 use lee::AccountId;
 use logos_blockchain_core::mantle::ops::channel::ChannelId;
@@ -25,6 +26,11 @@ pub enum GenesisAction {
     SupplyBridgeAccount {
         balance: u128,
     },
+    /// Seeds a bridge-lock holder's initial bridgeable balance into genesis state.
+    SupplyBridgeLockHolding {
+        holder: AccountId,
+        amount: u128,
+    },
 }
 
 // TODO: Provide default values
@@ -53,6 +59,9 @@ pub struct SequencerConfig {
     /// Genesis configuration.
     #[serde(default)]
     pub genesis: Vec<GenesisAction>,
+    /// Cross-zone messaging configuration. `None` disables the watcher.
+    #[serde(default)]
+    pub cross_zone: Option<CrossZoneConfig>,
 }
 
 #[derive(Clone, Serialize, Deserialize)]

lez/sequencer/core/src/cross_zone_watcher.rs

@@ -0,0 +1,185 @@
+use std::time::Duration;
+
+use common::{block::Block, transaction::LeeTransaction};
+use cross_zone::{build_dispatch_from_emission, extract_emission};
+use futures::StreamExt as _;
+use lee::PublicKey;
+use lee_core::program::ProgramId;
+use log::{debug, error, info, warn};
+use logos_blockchain_core::mantle::ops::channel::ChannelId;
+use logos_blockchain_zone_sdk::{
+    CommonHttpClient, ZoneMessage, adapter::NodeHttpClient, indexer::ZoneIndexer,
+};
+use mempool::MemPoolHandle;
+
+use crate::{
+    TransactionOrigin,
+    config::{BedrockConfig, CrossZoneConfig},
+};
+
+/// Spawns one watcher task per configured peer.
+///
+/// Each task reads the peer's finalized blocks from Bedrock, recognizes outbound
+/// messages addressed to this zone, and injects the matching inbox dispatch as a
+/// sequencer-origin transaction into the local mempool.
+pub fn spawn_watchers(
+    bedrock_config: &BedrockConfig,
+    cross_zone: &CrossZoneConfig,
+    poll_interval: Duration,
+    mempool_handle: &MemPoolHandle<(TransactionOrigin, LeeTransaction)>,
+) {
+    let self_zone: [u8; 32] = *bedrock_config.channel_id.as_ref();
+
+    for peer in cross_zone.peers.clone() {
+        let node = NodeHttpClient::new(
+            CommonHttpClient::new(bedrock_config.auth.clone().map(Into::into)),
+            bedrock_config.node_url.clone(),
+        );
+        let expected_pubkey = peer.expected_block_signing_pubkey.map(|bytes| {
+            PublicKey::try_new(bytes).expect("configured peer block-signing pubkey is a valid key")
+        });
+        tokio::spawn(watch_peer(
+            ZoneIndexer::new(ChannelId::from(peer.channel_id), node),
+            peer.channel_id,
+            peer.allowed_targets,
+            expected_pubkey,
+            self_zone,
+            poll_interval,
+            mempool_handle.clone(),
+        ));
+    }
+}
+
+#[expect(
+    clippy::infinite_loop,
+    reason = "the peer watcher runs for the lifetime of the sequencer process"
+)]
+async fn watch_peer(
+    zone_indexer: ZoneIndexer<NodeHttpClient>,
+    peer_zone: [u8; 32],
+    allowed_targets: Vec<ProgramId>,
+    expected_pubkey: Option<PublicKey>,
+    self_zone: [u8; 32],
+    poll_interval: Duration,
+    mempool_handle: MemPoolHandle<(TransactionOrigin, LeeTransaction)>,
+) {
+    info!(
+        "Cross-zone watcher started for peer {}",
+        hex::encode(peer_zone)
+    );
+
+    let mut cursor = None;
+    loop {
+        let stream = match zone_indexer.next_messages(cursor).await {
+            Ok(stream) => stream,
+            Err(err) => {
+                error!(
+                    "Watcher next_messages failed for peer {}: {err}",
+                    hex::encode(peer_zone)
+                );
+                tokio::time::sleep(poll_interval).await;
+                continue;
+            }
+        };
+        let mut stream = std::pin::pin!(stream);
+
+        while let Some((msg, slot)) = stream.next().await {
+            let zone_block = match msg {
+                ZoneMessage::Block(block) => block,
+                ZoneMessage::Deposit(_) | ZoneMessage::Withdraw(_) => continue,
+            };
+            match borsh::from_slice::<Block>(&zone_block.data) {
+                Ok(block) => {
+                    debug!(
+                        "Watcher observed finalized peer {} block {}",
+                        hex::encode(peer_zone),
+                        block.header.block_id
+                    );
+                    // Reject blocks not signed by the pinned peer key (equivocation):
+                    // the channel signer is authenticated by the zone-sdk, but that
+                    // does not prove the peer's honest sequencer produced the block.
+                    if expected_pubkey
+                        .as_ref()
+                        .is_some_and(|pk| !block.is_signed_by(pk))
+                    {
+                        warn!(
+                            "Watcher dropping peer {} block {}: block-signing key does not match the pinned key",
+                            hex::encode(peer_zone),
+                            block.header.block_id
+                        );
+                    } else {
+                        deliver_block(
+                            &block,
+                            peer_zone,
+                            self_zone,
+                            &allowed_targets,
+                            &mempool_handle,
+                        )
+                        .await;
+                    }
+                }
+                Err(err) => error!("Watcher failed to deserialize peer block: {err}"),
+            }
+            cursor = Some(slot);
+        }
+
+        // Stream ended (caught up to the peer's last finalized block); poll again.
+        tokio::time::sleep(poll_interval).await;
+    }
+}
+
+/// Scans one peer block for outbound messages and injects a dispatch per match.
+async fn deliver_block(
+    block: &Block,
+    peer_zone: [u8; 32],
+    self_zone: [u8; 32],
+    allowed_targets: &[ProgramId],
+    mempool_handle: &MemPoolHandle<(TransactionOrigin, LeeTransaction)>,
+) {
+    for (index, tx) in block.body.transactions.iter().enumerate() {
+        let LeeTransaction::Public(public_tx) = tx else {
+            continue;
+        };
+        let message = public_tx.message();
+        let Some(emission) = extract_emission(message.program_id, &message.instruction_data) else {
+            continue;
+        };
+
+        if emission.target_zone != self_zone {
+            continue;
+        }
+        if !allowed_targets.contains(&emission.target_program_id) {
+            warn!(
+                "Watcher dropping message to disallowed target from peer {}",
+                hex::encode(peer_zone)
+            );
+            continue;
+        }
+
+        let dispatch = build_dispatch_from_emission(
+            peer_zone,
+            block.header.block_id,
+            u32::try_from(index).unwrap_or(u32::MAX),
+            message.program_id,
+            emission.target_program_id,
+            &emission.target_accounts,
+            emission.payload,
+        );
+
+        match mempool_handle
+            .push((
+                TransactionOrigin::Sequencer,
+                LeeTransaction::Public(dispatch),
+            ))
+            .await
+        {
+            Ok(()) => info!(
+                "Watcher injected cross-zone dispatch from peer {} block {} tx {}",
+                hex::encode(peer_zone),
+                block.header.block_id,
+                index
+            ),
+            Err(err) => error!("Watcher failed to enqueue inbox dispatch: {err}"),
+        }
+    }
+}

lez/sequencer/core/src/lib.rs

@@ -32,6 +32,7 @@ use crate::{
 pub mod block_publisher;
 pub mod block_store;
 pub mod config;
+pub mod cross_zone_watcher;
 
 #[cfg(feature = "mock")]
 pub mod mock;
@@ -181,6 +182,17 @@ impl<BP: BlockPublisherTrait> SequencerCore<BP> {
             }
         }
 
+        // Cross-zone messaging: start a watcher per configured peer. The inbox
+        // config account is seeded into genesis state in `build_genesis_state`.
+        if let Some(cross_zone) = &config.cross_zone {
+            cross_zone_watcher::spawn_watchers(
+                &config.bedrock_config,
+                cross_zone,
+                config.block_create_timeout,
+                &mempool_handle,
+            );
+        }
+
         let sequencer_core = Self {
             state,
             store,
@@ -628,14 +640,18 @@ fn build_genesis_state(config: &SequencerConfig) -> (lee::V03State, Vec<LeeTrans
     let genesis_txs = config
         .genesis
         .iter()
-        .map(|genesis_tx| match genesis_tx {
+        .filter_map(|genesis_tx| match genesis_tx {
             GenesisAction::SupplyAccount {
                 account_id,
                 balance,
-            } => build_supply_account_genesis_transaction(account_id, *balance),
+            } => Some(build_supply_account_genesis_transaction(
+                account_id, *balance,
+            )),
             GenesisAction::SupplyBridgeAccount { balance } => {
-                build_supply_bridge_account_genesis_transaction(*balance)
+                Some(build_supply_bridge_account_genesis_transaction(*balance))
             }
+            // Force-inserted below: bridge_lock has no mint transaction.
+            GenesisAction::SupplyBridgeLockHolding { .. } => None,
         })
         .chain(std::iter::once(clock_invocation(0)))
         .inspect(|tx| {
@@ -646,9 +662,36 @@ fn build_genesis_state(config: &SequencerConfig) -> (lee::V03State, Vec<LeeTrans
         .map(LeeTransaction::Public)
         .collect();
 
+    // Seed bridge-lock holder balances directly: they are not produced by any tx.
+    for action in &config.genesis {
+        if let GenesisAction::SupplyBridgeLockHolding { holder, amount } = action {
+            let (holder_id, account) = cross_zone::build_holding_account(*holder, *amount);
+            state.insert_genesis_account(holder_id, account);
+        }
+    }
+
+    // Seed this zone's cross-zone inbox config so the inbox guest can authorize
+    // inbound peer messages (zone-specific config, not produced by any tx).
+    if let Some(cross_zone) = &config.cross_zone {
+        let self_zone = *config.bedrock_config.channel_id.as_ref();
+        let (config_id, config_account) =
+            cross_zone::build_inbox_config_account(self_zone, cross_zone);
+        state.insert_genesis_account(config_id, config_account);
+    }
+
     (state, genesis_txs)
 }
 
+/// Whether a program may only be invoked by sequencer-origin transactions.
+///
+/// The cross-zone inbox is injected solely by the watcher; a user-submitted call
+/// must be rejected at ingress, since `TransactionOrigin` is not carried in the
+/// block.
+#[must_use]
+pub fn is_sequencer_only_program(program_id: lee::ProgramId) -> bool {
+    cross_zone::is_sequencer_only_program(program_id)
+}
+
 fn build_supply_account_genesis_transaction(
     account_id: &AccountId,
     balance: u128,

lez/sequencer/core/src/tests.rs

@@ -33,6 +33,7 @@ use crate::{
     block_store::SequencerStore,
     build_genesis_state,
     config::{BedrockConfig, SequencerConfig},
+    is_sequencer_only_program,
     mock::SequencerCoreWithMockClients,
 };
 
@@ -59,9 +60,21 @@ fn setup_sequencer_config() -> SequencerConfig {
         },
         retry_pending_blocks_timeout: Duration::from_mins(4),
         genesis: vec![],
+        cross_zone: None,
     }
 }
 
+#[test]
+fn only_the_cross_zone_inbox_is_sequencer_only() {
+    assert!(is_sequencer_only_program(programs::cross_zone_inbox().id()));
+    assert!(!is_sequencer_only_program(
+        programs::cross_zone_outbox().id()
+    ));
+    assert!(!is_sequencer_only_program(programs::wrapped_token().id()));
+    assert!(!is_sequencer_only_program(programs::ping_sender().id()));
+    assert!(!is_sequencer_only_program(programs::clock().id()));
+}
+
 fn create_signing_key_for_account1() -> lee::PrivateKey {
     initial_pub_accounts_private_keys()[0].pub_sign_key.clone()
 }

lez/sequencer/service/src/service.rs

@@ -74,6 +74,20 @@ impl<BC: BlockPublisherTrait + Send + 'static> sequencer_service_rpc::RpcServer
                 )
             })?;
 
+        // Sequencer-only programs (the cross-zone inbox) are injected by the
+        // watcher; a user must not invoke them top-level, or anyone could forge
+        // an inbound cross-zone delivery. Chained user calls are already rejected
+        // by the inbox guest's caller-is-none assertion.
+        if let LeeTransaction::Public(public_tx) = &authenticated_tx
+            && sequencer_core::is_sequencer_only_program(public_tx.message().program_id)
+        {
+            return Err(ErrorObjectOwned::owned(
+                ErrorCode::InvalidParams.code(),
+                "Program is sequencer-only and cannot be invoked by a user transaction".to_owned(),
+                None::<()>,
+            ));
+        }
+
         self.mempool_handle
             .push((TransactionOrigin::User, authenticated_tx))
             .await

lez/testnet_initial_state/Cargo.toml

@@ -10,6 +10,7 @@ lee.workspace = true
 lee_core.workspace = true
 system_accounts.workspace = true
 programs.workspace = true
+wrapped_token_core.workspace = true
 
 serde.workspace = true
 

lez/testnet_initial_state/src/lib.rs

@@ -258,9 +258,30 @@ fn initial_public_accounts() -> HashMap<AccountId, Account> {
                 .into_iter()
                 .map(|clock_id| (clock_id, system_accounts::clock_account())),
         )
+        .chain(std::iter::once(wrapped_token_config_account()))
         .collect()
 }
 
+/// The wrapped-token config account.
+///
+/// Seeded so the `wrapped_token` guest can pin its authorized minter (the
+/// cross-zone inbox) without importing the inbox id. Fixed for every zone, so it
+/// lives in the shared initial state.
+fn wrapped_token_config_account() -> (AccountId, Account) {
+    let wrapped_token_id = programs::wrapped_token().id();
+    (
+        wrapped_token_core::config_account_id(wrapped_token_id),
+        Account {
+            program_owner: wrapped_token_id,
+            data: wrapped_token_core::minter_bytes(programs::cross_zone_inbox().id())
+                .to_vec()
+                .try_into()
+                .expect("minter id fits in account data"),
+            ..Default::default()
+        },
+    )
+}
+
 fn initial_programs() -> Vec<Program> {
     vec![
         programs::authenticated_transfer(),
@@ -271,6 +292,12 @@ fn initial_programs() -> Vec<Program> {
         programs::vault(),
         programs::faucet(),
         programs::bridge(),
+        programs::cross_zone_outbox(),
+        programs::cross_zone_inbox(),
+        programs::ping_sender(),
+        programs::ping_receiver(),
+        programs::bridge_lock(),
+        programs::wrapped_token(),
     ]
 }
 

programs/bridge_lock/core/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "bridge_lock_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+lee = { workspace = true, optional = true }
+
+[features]
+# Host-only genesis helper; pulls `lee`, so the risc0 guest builds without it.
+host = ["dep:lee"]

programs/bridge_lock/core/src/lib.rs

@@ -0,0 +1,92 @@
+//! Core types for the bridge-lock program, the source side of the cross-zone
+//! token bridge. A holder locks part of their balance into an escrow and emits a
+//! cross-zone message minting the wrapped token on the target zone.
+
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const ESCROW_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/BridgeLockEscrow/0000/";
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Lock `amount` of the holder's balance and emit a cross-zone message
+    /// minting the wrapped token on `target_zone`. The emission fields mirror
+    /// `cross_zone_outbox::Instruction::Emit` so the watcher reads them directly.
+    ///
+    /// Required accounts (3): holder holding (authorized), escrow PDA, outbox PDA.
+    Lock {
+        amount: u128,
+        target_zone: [u8; 32],
+        target_program_id: ProgramId,
+        target_accounts: Vec<[u8; 32]>,
+        payload: Vec<u8>,
+        outbox_program_id: ProgramId,
+        ordinal: u32,
+    },
+}
+
+/// PDA accumulating all locked balance on this zone.
+#[must_use]
+pub fn escrow_account_id(bridge_lock_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&bridge_lock_id, &escrow_seed())
+}
+
+#[must_use]
+pub fn escrow_seed() -> PdaSeed {
+    PdaSeed::new(ESCROW_SEED_DOMAIN)
+}
+
+/// Reads a bridgeable balance from account data; empty data is a zero balance.
+#[must_use]
+pub fn read_balance(data: &[u8]) -> u128 {
+    if data.len() < 16 {
+        return 0;
+    }
+    u128::from_le_bytes(data[..16].try_into().unwrap_or_else(|_| unreachable!()))
+}
+
+#[must_use]
+pub fn balance_bytes(amount: u128) -> [u8; 16] {
+    amount.to_le_bytes()
+}
+
+/// Builds the genesis holding account funding a holder's bridgeable balance:
+/// owned by bridge_lock, data is the LE balance, at the holder's account id. It
+/// is not produced by any transaction, so the sequencer and the indexer both
+/// seed it through this one builder to keep their genesis states identical.
+#[cfg(feature = "host")]
+#[must_use]
+pub fn build_holding_account(
+    holder: AccountId,
+    amount: u128,
+) -> (AccountId, lee_core::account::Account) {
+    let account = lee_core::account::Account {
+        program_owner: lee::program::Program::bridge_lock().id(),
+        data: balance_bytes(amount)
+            .to_vec()
+            .try_into()
+            .expect("balance fits in account data"),
+        ..Default::default()
+    };
+    (holder, account)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn balance_round_trips() {
+        assert_eq!(read_balance(&balance_bytes(7)), 7);
+        assert_eq!(read_balance(&[]), 0);
+    }
+
+    #[test]
+    fn escrow_is_stable() {
+        let id: ProgramId = [4; 8];
+        assert_eq!(escrow_account_id(id), escrow_account_id(id));
+    }
+}

programs/cross_zone_inbox/core/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "cross_zone_inbox_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+risc0-zkvm.workspace = true
+borsh.workspace = true
+lee = { workspace = true, optional = true }
+ping_core = { workspace = true, optional = true }
+bridge_lock_core = { workspace = true, optional = true }
+
+[features]
+# Host-only transaction builder and emission extractor; pull `lee` and the
+# emitter cores, so the risc0 guest builds without them.
+host = ["dep:lee", "dep:ping_core", "dep:bridge_lock_core"]

programs/cross_zone_inbox/core/src/lib.rs

@@ -0,0 +1,378 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+use borsh::{BorshDeserialize, BorshSerialize};
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+/// Raw 32-byte zone (channel) id; the host maps it to the zone-sdk `ChannelId`.
+pub type ZoneId = [u8; 32];
+
+/// Block-signing public key pinned per peer zone.
+pub type ExpectedPubkey = [u8; 32];
+
+/// Content-addressed replay key for a delivered message.
+pub type MessageKey = [u8; 32];
+
+/// Source blocks per seen-set shard, so no single seen account grows without bound.
+pub const EPOCH_BLOCKS: u64 = 10_000;
+
+const MESSAGE_KEY_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/CrossZoneMsgKey/00000/";
+const INBOX_CONFIG_SEED: [u8; 32] = *b"/LEZ/v0.3/CrossZoneInboxCfg/000/";
+const INBOX_SEEN_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/CrossZoneInboxSeen/00/";
+
+/// A peer zone whose outbox a zone watches for inbound cross-zone messages.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct CrossZonePeer {
+    /// The peer's Bedrock channel; its 32 bytes double as the peer's zone id.
+    pub channel_id: ZoneId,
+    /// Programs on the local zone a message from this peer is allowed to target.
+    pub allowed_targets: Vec<ProgramId>,
+    /// The peer's block-signing public key, pinned to reject blocks inscribed by
+    /// anyone other than that zone's sequencer. `None` skips the check (the
+    /// channel signer is still authenticated by the zone-sdk).
+    #[serde(default)]
+    pub expected_block_signing_pubkey: Option<[u8; 32]>,
+}
+
+/// Cross-zone configuration shared by a zone's sequencer (watcher) and indexer
+/// (verifier): the peers it reads from Bedrock and, per peer, the local programs
+/// they may deliver to.
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct CrossZoneConfig {
+    pub peers: Vec<CrossZonePeer>,
+}
+
+/// A finalized outbound message observed on a peer zone, addressed to a program
+/// on this zone. The watcher fills it from the peer's block; it is never
+/// self-reported by a user.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct CrossZoneMessage {
+    pub src_zone: ZoneId,
+    pub src_block_id: u64,
+    pub src_tx_index: u32,
+    pub src_program_id: ProgramId,
+    pub target_program_id: ProgramId,
+    pub payload: Vec<u8>,
+    /// Reserved for a future source-state proof; MUST be `None` in v1.
+    pub l1_inclusion_witness: Option<Vec<u8>>,
+}
+
+/// Peer and per-peer target allowlists, plus this inbox's own zone id.
+#[derive(
+    Clone, Debug, Default, PartialEq, Eq, Serialize, Deserialize, BorshSerialize, BorshDeserialize,
+)]
+pub struct InboxConfig {
+    pub self_zone: ZoneId,
+    pub allowed_peers: BTreeMap<ZoneId, ExpectedPubkey>,
+    pub allowed_targets: BTreeMap<ZoneId, Vec<ProgramId>>,
+}
+
+impl InboxConfig {
+    /// Borsh-encoded form stored in the inbox config account.
+    #[must_use]
+    pub fn to_bytes(&self) -> Vec<u8> {
+        borsh::to_vec(self).expect("InboxConfig serializes")
+    }
+
+    /// Decodes an [`InboxConfig`] from account data.
+    pub fn from_bytes(bytes: &[u8]) -> borsh::io::Result<Self> {
+        borsh::from_slice(bytes)
+    }
+}
+
+/// The replay keys seen for one `(src_zone, epoch)` shard.
+#[derive(Clone, Debug, Default, PartialEq, Eq, BorshSerialize, BorshDeserialize)]
+pub struct SeenShard(pub BTreeSet<MessageKey>);
+
+impl SeenShard {
+    /// Decodes a shard from account data; empty data is an empty shard.
+    pub fn from_bytes(bytes: &[u8]) -> borsh::io::Result<Self> {
+        if bytes.is_empty() {
+            return Ok(Self::default());
+        }
+        borsh::from_slice(bytes)
+    }
+
+    #[must_use]
+    pub fn to_bytes(&self) -> Vec<u8> {
+        borsh::to_vec(self).expect("SeenShard serializes")
+    }
+
+    #[must_use]
+    pub fn contains(&self, key: &MessageKey) -> bool {
+        self.0.contains(key)
+    }
+
+    /// Inserts a key; returns true if it was newly inserted.
+    pub fn insert(&mut self, key: MessageKey) -> bool {
+        self.0.insert(key)
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Delivers a finalized peer message to its target program.
+    Dispatch(CrossZoneMessage),
+}
+
+/// Content-addressed replay key: `(src_zone, src_block_id, src_tx_index)` hashed
+/// under a domain separator. Watcher-independent and immune to proof
+/// malleability, since it keys on block id plus index rather than a tx hash.
+#[must_use]
+pub fn message_key(src_zone: &ZoneId, src_block_id: u64, src_tx_index: u32) -> MessageKey {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let mut bytes = Vec::with_capacity(MESSAGE_KEY_DOMAIN.len() + 32 + 8 + 4);
+    bytes.extend_from_slice(&MESSAGE_KEY_DOMAIN);
+    bytes.extend_from_slice(src_zone);
+    bytes.extend_from_slice(&src_block_id.to_le_bytes());
+    bytes.extend_from_slice(&src_tx_index.to_le_bytes());
+
+    Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!())
+}
+
+/// The config account holding the allowlists.
+#[must_use]
+pub fn inbox_config_account_id(inbox_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&inbox_id, &PdaSeed::new(INBOX_CONFIG_SEED))
+}
+
+/// The seen-set shard for the `(src_zone, epoch)` the message falls in.
+#[must_use]
+pub fn inbox_seen_shard_account_id(
+    inbox_id: ProgramId,
+    src_zone: &ZoneId,
+    src_block_id: u64,
+) -> AccountId {
+    AccountId::for_public_pda(&inbox_id, &inbox_seen_shard_seed(src_zone, src_block_id))
+}
+
+/// Seed of the seen-shard PDA, exposed so the guest can claim the account.
+#[must_use]
+pub fn inbox_seen_shard_seed(src_zone: &ZoneId, src_block_id: u64) -> PdaSeed {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let src_epoch = src_block_id / EPOCH_BLOCKS;
+    let mut bytes = Vec::with_capacity(INBOX_SEEN_SEED_DOMAIN.len() + 32 + 8);
+    bytes.extend_from_slice(&INBOX_SEEN_SEED_DOMAIN);
+    bytes.extend_from_slice(src_zone);
+    bytes.extend_from_slice(&src_epoch.to_le_bytes());
+
+    let seed: [u8; 32] = Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    PdaSeed::new(seed)
+}
+
+/// Builds the sequencer-origin dispatch transaction. Pure, so the watcher's
+/// injected tx and the indexer's re-derived tx are byte-identical for the same
+/// inputs (the basis of the Option B check). `target_account_ids` are the
+/// inbox's chained-call targets; deriving them is target-specific.
+#[cfg(feature = "host")]
+#[must_use]
+pub fn build_inbox_dispatch_tx(
+    inbox_id: ProgramId,
+    msg: &CrossZoneMessage,
+    target_account_ids: Vec<AccountId>,
+) -> lee::PublicTransaction {
+    let mut account_ids = Vec::with_capacity(2 + target_account_ids.len());
+    account_ids.push(inbox_config_account_id(inbox_id));
+    account_ids.push(inbox_seen_shard_account_id(
+        inbox_id,
+        &msg.src_zone,
+        msg.src_block_id,
+    ));
+    account_ids.extend(target_account_ids);
+
+    let message = lee::public_transaction::Message::try_new(
+        inbox_id,
+        account_ids,
+        vec![],
+        Instruction::Dispatch(msg.clone()),
+    )
+    .expect("inbox dispatch instruction must serialize");
+
+    lee::PublicTransaction::new(
+        message,
+        lee::public_transaction::WitnessSet::from_raw_parts(vec![]),
+    )
+}
+
+/// The cross-zone emission fields a watcher or verifier reads off a source
+/// transaction, common to every emitter program.
+#[cfg(feature = "host")]
+pub struct Emission {
+    pub target_zone: ZoneId,
+    pub target_program_id: ProgramId,
+    pub target_accounts: Vec<[u8; 32]>,
+    pub payload: Vec<u8>,
+}
+
+/// Extracts the cross-zone emission from a source transaction, recognizing the
+/// known emitter programs. Returns `None` for any other program. The watcher and
+/// verifier both use this so they agree on what a given source tx emits.
+///
+/// Option A: each emitter is decoded explicitly. The principled alternative is to
+/// read the outbox PDA write, which would need re-execution of the source tx.
+#[cfg(feature = "host")]
+#[must_use]
+pub fn extract_emission(
+    program_id: ProgramId,
+    instruction_data: &[u32],
+    ping_sender_id: ProgramId,
+    bridge_lock_id: ProgramId,
+) -> Option<Emission> {
+    if program_id == ping_sender_id {
+        let ping_core::SenderInstruction::Send {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ..
+        } = risc0_zkvm::serde::from_slice(instruction_data).ok()?;
+        Some(Emission {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+        })
+    } else if program_id == bridge_lock_id {
+        let bridge_lock_core::Instruction::Lock {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+            ..
+        } = risc0_zkvm::serde::from_slice(instruction_data).ok()?;
+        Some(Emission {
+            target_zone,
+            target_program_id,
+            target_accounts,
+            payload,
+        })
+    } else {
+        None
+    }
+}
+
+/// Builds the dispatch transaction for one peer emission. Both the sequencer's
+/// watcher and the indexer's verifier go through this so their transactions are
+/// byte-identical for the same emission (the basis of the Option B check).
+#[cfg(feature = "host")]
+#[must_use]
+pub fn build_dispatch_from_emission(
+    inbox_id: ProgramId,
+    src_zone: ZoneId,
+    src_block_id: u64,
+    src_tx_index: u32,
+    src_program_id: ProgramId,
+    target_program_id: ProgramId,
+    target_accounts: &[[u8; 32]],
+    payload: Vec<u8>,
+) -> lee::PublicTransaction {
+    let msg = CrossZoneMessage {
+        src_zone,
+        src_block_id,
+        src_tx_index,
+        src_program_id,
+        target_program_id,
+        payload,
+        l1_inclusion_witness: None,
+    };
+    let target_ids = target_accounts
+        .iter()
+        .copied()
+        .map(AccountId::new)
+        .collect();
+    build_inbox_dispatch_tx(inbox_id, &msg, target_ids)
+}
+
+/// Builds the inbox config account a zone seeds into genesis state so the inbox
+/// guest can authorize inbound peer messages. The sequencer and indexer seed the
+/// same account from the same config, keeping their replayed state consistent.
+#[cfg(feature = "host")]
+#[must_use]
+pub fn build_inbox_config_account(
+    self_zone: ZoneId,
+    cross_zone: &CrossZoneConfig,
+) -> (AccountId, lee_core::account::Account) {
+    let inbox_id = lee::program::Program::cross_zone_inbox().id();
+
+    let mut allowed_targets = BTreeMap::new();
+    for peer in &cross_zone.peers {
+        allowed_targets.insert(peer.channel_id, peer.allowed_targets.clone());
+    }
+    let config = InboxConfig {
+        self_zone,
+        allowed_peers: BTreeMap::new(),
+        allowed_targets,
+    };
+
+    let account = lee_core::account::Account {
+        program_owner: inbox_id,
+        balance: 0,
+        data: config
+            .to_bytes()
+            .try_into()
+            .expect("inbox config fits in account data"),
+        nonce: 0_u128.into(),
+    };
+    (inbox_config_account_id(inbox_id), account)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn zone(b: u8) -> ZoneId {
+        [b; 32]
+    }
+
+    #[test]
+    fn message_key_is_stable_and_content_addressed() {
+        assert_eq!(message_key(&zone(1), 7, 3), message_key(&zone(1), 7, 3));
+        assert_ne!(message_key(&zone(1), 7, 3), message_key(&zone(2), 7, 3));
+        assert_ne!(message_key(&zone(1), 7, 3), message_key(&zone(1), 8, 3));
+        assert_ne!(message_key(&zone(1), 7, 3), message_key(&zone(1), 7, 4));
+    }
+
+    #[test]
+    fn seen_shards_split_on_epoch_boundary() {
+        let id: ProgramId = [9; 8];
+        assert_eq!(
+            inbox_seen_shard_account_id(id, &zone(1), 0),
+            inbox_seen_shard_account_id(id, &zone(1), EPOCH_BLOCKS - 1),
+        );
+        assert_ne!(
+            inbox_seen_shard_account_id(id, &zone(1), EPOCH_BLOCKS - 1),
+            inbox_seen_shard_account_id(id, &zone(1), EPOCH_BLOCKS),
+        );
+    }
+
+    #[cfg(feature = "host")]
+    #[test]
+    fn build_inbox_dispatch_tx_is_deterministic() {
+        let inbox: ProgramId = [5; 8];
+        let msg = CrossZoneMessage {
+            src_zone: zone(1),
+            src_block_id: 42,
+            src_tx_index: 2,
+            src_program_id: [6; 8],
+            target_program_id: [7; 8],
+            payload: vec![1, 2, 3, 4],
+            l1_inclusion_witness: None,
+        };
+        let targets = vec![AccountId::new([8; 32]), AccountId::new([9; 32])];
+
+        let tx1 = build_inbox_dispatch_tx(inbox, &msg, targets.clone());
+        let tx2 = build_inbox_dispatch_tx(inbox, &msg, targets);
+        assert_eq!(tx1, tx2);
+    }
+}

programs/cross_zone_outbox/core/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "cross_zone_outbox_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+risc0-zkvm.workspace = true
+borsh.workspace = true

programs/cross_zone_outbox/core/src/lib.rs

@@ -0,0 +1,93 @@
+use borsh::{BorshDeserialize, BorshSerialize};
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+/// Raw 32-byte zone (channel) id; the host maps it to the zone-sdk `ChannelId`.
+pub type ZoneId = [u8; 32];
+
+const OUTBOX_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/CrossZoneOutbox/00000/";
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Records an outbound cross-zone message as a write to a self-owned PDA.
+    ///
+    /// Required accounts (1):
+    /// - Outbox PDA account
+    Emit {
+        target_zone: ZoneId,
+        target_program_id: ProgramId,
+        /// Accounts the destination inbox must hand to the target program's
+        /// chained call. The emitter specifies them; the watcher forwards them
+        /// verbatim so the inbox stays target-agnostic.
+        target_accounts: Vec<[u8; 32]>,
+        payload: Vec<u8>,
+        ordinal: u32,
+    },
+}
+
+/// The message as stored in an outbox PDA. The destination zone's watcher reads
+/// this from the inscribed block; the source coordinates are filled by the
+/// watcher, not stored here.
+#[derive(Clone, Debug, PartialEq, Eq, BorshSerialize, BorshDeserialize)]
+pub struct OutboxRecord {
+    pub target_zone: ZoneId,
+    pub target_program_id: ProgramId,
+    pub target_accounts: Vec<[u8; 32]>,
+    pub payload: Vec<u8>,
+}
+
+impl OutboxRecord {
+    /// Borsh-encoded form stored in the outbox PDA's account data.
+    #[must_use]
+    pub fn to_bytes(&self) -> Vec<u8> {
+        borsh::to_vec(self).expect("OutboxRecord serializes")
+    }
+
+    /// Decodes an [`OutboxRecord`] from account data.
+    pub fn from_bytes(bytes: &[u8]) -> borsh::io::Result<Self> {
+        borsh::from_slice(bytes)
+    }
+}
+
+/// PDA holding one emitted message, keyed by destination zone and a per-zone
+/// ordinal.
+#[must_use]
+pub fn outbox_pda(outbox_id: ProgramId, target_zone: &ZoneId, ordinal: u32) -> AccountId {
+    AccountId::for_public_pda(&outbox_id, &outbox_pda_seed(target_zone, ordinal))
+}
+
+/// Seed of an outbox message PDA, exposed so the guest can claim the account.
+#[must_use]
+pub fn outbox_pda_seed(target_zone: &ZoneId, ordinal: u32) -> PdaSeed {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let mut bytes = Vec::with_capacity(OUTBOX_SEED_DOMAIN.len() + target_zone.len() + 4);
+    bytes.extend_from_slice(&OUTBOX_SEED_DOMAIN);
+    bytes.extend_from_slice(target_zone);
+    bytes.extend_from_slice(&ordinal.to_le_bytes());
+
+    let seed: [u8; 32] = Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    PdaSeed::new(seed)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn outbox_pda_is_unique_per_zone_and_ordinal() {
+        let id: ProgramId = [3; 8];
+        let zone_a = [1; 32];
+        let zone_b = [2; 32];
+
+        assert_eq!(outbox_pda(id, &zone_a, 0), outbox_pda(id, &zone_a, 0));
+        assert_ne!(outbox_pda(id, &zone_a, 0), outbox_pda(id, &zone_a, 1));
+        assert_ne!(outbox_pda(id, &zone_a, 0), outbox_pda(id, &zone_b, 0));
+    }
+}

programs/ping/core/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "ping_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }

programs/ping/core/src/lib.rs

@@ -0,0 +1,38 @@
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const PING_RECORD_SEED: [u8; 32] = *b"/LEZ/v0.3/PingRecord/0000000000/";
+
+/// Instruction delivered to `ping_receiver` by the inbox: record the payload.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum ReceiverInstruction {
+    Record { payload: Vec<u8> },
+}
+
+/// Instruction to `ping_sender`: forwarded verbatim into `cross_zone_outbox::Instruction::Emit`.
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum SenderInstruction {
+    Send {
+        outbox_program_id: ProgramId,
+        target_zone: [u8; 32],
+        target_program_id: ProgramId,
+        target_accounts: Vec<[u8; 32]>,
+        payload: Vec<u8>,
+        ordinal: u32,
+    },
+}
+
+/// The account a `ping_receiver` records the latest delivered payload into.
+#[must_use]
+pub fn ping_record_pda(receiver_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&receiver_id, &ping_record_seed())
+}
+
+/// Seed of the record PDA, exposed so the guest can claim the account.
+#[must_use]
+pub fn ping_record_seed() -> PdaSeed {
+    PdaSeed::new(PING_RECORD_SEED)
+}

programs/wrapped_token/core/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "wrapped_token_core"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+lee_core.workspace = true
+serde = { workspace = true, features = ["alloc"] }
+risc0-zkvm.workspace = true

programs/wrapped_token/core/src/lib.rs

@@ -0,0 +1,121 @@
+//! Core types for the wrapped-token program, the destination side of the
+//! cross-zone bridge. Only the cross-zone inbox may mint; the guest enforces
+//! this by reading the authorized minter from a genesis-seeded config account.
+
+use lee_core::{
+    account::AccountId,
+    program::{PdaSeed, ProgramId},
+};
+use serde::{Deserialize, Serialize};
+
+const CONFIG_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/WrappedTokenConfig/00/";
+const HOLDING_SEED_DOMAIN: [u8; 32] = *b"/LEZ/v0.3/WrappedTokenHold/00000";
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Instruction {
+    /// Credit `amount` wrapped tokens to `recipient`'s holding. Delivered only by
+    /// the cross-zone inbox.
+    ///
+    /// Required accounts (2): the wrapped-token config PDA, then the recipient's
+    /// holding PDA.
+    Mint { recipient: [u8; 32], amount: u128 },
+}
+
+/// PDA holding the authorized minter program id (the cross-zone inbox), seeded at
+/// genesis so the guest can pin its caller without importing the inbox image id.
+#[must_use]
+pub fn config_account_id(wrapped_token_id: ProgramId) -> AccountId {
+    AccountId::for_public_pda(&wrapped_token_id, &config_seed())
+}
+
+#[must_use]
+pub fn config_seed() -> PdaSeed {
+    PdaSeed::new(CONFIG_SEED_DOMAIN)
+}
+
+/// PDA holding one recipient's wrapped-token balance.
+#[must_use]
+pub fn holding_account_id(wrapped_token_id: ProgramId, recipient: &[u8; 32]) -> AccountId {
+    AccountId::for_public_pda(&wrapped_token_id, &holding_seed(recipient))
+}
+
+#[must_use]
+pub fn holding_seed(recipient: &[u8; 32]) -> PdaSeed {
+    use risc0_zkvm::sha::{Impl, Sha256 as _};
+
+    let mut bytes = Vec::with_capacity(HOLDING_SEED_DOMAIN.len() + recipient.len());
+    bytes.extend_from_slice(&HOLDING_SEED_DOMAIN);
+    bytes.extend_from_slice(recipient);
+    let seed: [u8; 32] = Impl::hash_bytes(&bytes)
+        .as_bytes()
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    PdaSeed::new(seed)
+}
+
+/// Encodes the authorized minter program id for the config account's data.
+#[must_use]
+pub fn minter_bytes(minter: ProgramId) -> [u8; 32] {
+    let mut bytes = [0_u8; 32];
+    for (word, chunk) in minter.iter().zip(bytes.chunks_exact_mut(4)) {
+        chunk.copy_from_slice(&word.to_le_bytes());
+    }
+    bytes
+}
+
+/// Decodes the authorized minter program id from the config account's data.
+#[must_use]
+pub fn read_minter(data: &[u8]) -> Option<ProgramId> {
+    if data.len() < 32 {
+        return None;
+    }
+    let mut minter = [0_u32; 8];
+    for (word, chunk) in minter.iter_mut().zip(data[..32].chunks_exact(4)) {
+        *word = u32::from_le_bytes(chunk.try_into().unwrap_or_else(|_| unreachable!()));
+    }
+    Some(minter)
+}
+
+/// Reads a wrapped-token balance from account data; empty data is a zero balance.
+#[must_use]
+pub fn read_balance(data: &[u8]) -> u128 {
+    if data.len() < 16 {
+        return 0;
+    }
+    u128::from_le_bytes(data[..16].try_into().unwrap_or_else(|_| unreachable!()))
+}
+
+#[must_use]
+pub fn balance_bytes(amount: u128) -> [u8; 16] {
+    amount.to_le_bytes()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn minter_round_trips() {
+        let minter: ProgramId = [1, 2, 3, 4, 5, 6, 7, 8];
+        assert_eq!(read_minter(&minter_bytes(minter)), Some(minter));
+    }
+
+    #[test]
+    fn balance_round_trips() {
+        assert_eq!(read_balance(&balance_bytes(42)), 42);
+        assert_eq!(read_balance(&[]), 0);
+    }
+
+    #[test]
+    fn holding_is_unique_per_recipient() {
+        let id: ProgramId = [9; 8];
+        assert_ne!(
+            holding_account_id(id, &[1; 32]),
+            holding_account_id(id, &[2; 32])
+        );
+        assert_eq!(
+            holding_account_id(id, &[1; 32]),
+            holding_account_id(id, &[1; 32])
+        );
+    }
+}

test_fixtures/src/bin/regenerate_test_fixture.rs

@@ -53,6 +53,8 @@ async fn generate_prebuilt_fixture(dest: &Path) -> Result<()> {
         config::SequencerPartialConfig::default(),
         bedrock_addr,
         genesis,
+        config::bedrock_channel_id(),
+        None,
     )
     .await
     .context("Failed to setup Sequencer for fixture generation")?;

test_fixtures/src/config.rs

@@ -6,7 +6,7 @@ use indexer_service::{ChannelId, ClientConfig, IndexerConfig};
 use key_protocol::key_management::{KeyChain, secret_holders::SeedHolder};
 use lee::{AccountId, PrivateKey, PublicKey};
 use lee_core::Identifier;
-use sequencer_core::config::{BedrockConfig, GenesisAction, SequencerConfig};
+use sequencer_core::config::{BedrockConfig, CrossZoneConfig, GenesisAction, SequencerConfig};
 use url::Url;
 use wallet::config::WalletConfig;
 
@@ -80,6 +80,8 @@ pub fn sequencer_config(
     home: PathBuf,
     bedrock_addr: SocketAddr,
     genesis_transactions: Vec<GenesisAction>,
+    channel_id: ChannelId,
+    cross_zone: Option<CrossZoneConfig>,
 ) -> Result<SequencerConfig> {
     let SequencerPartialConfig {
         max_num_tx_in_block,
@@ -98,11 +100,12 @@ pub fn sequencer_config(
         genesis: genesis_transactions,
         signing_key: SEQUENCER_SIGNING_KEY,
         bedrock_config: BedrockConfig {
-            channel_id: bedrock_channel_id(),
+            channel_id,
             node_url: addr_to_url(UrlProtocol::Http, bedrock_addr)
                 .context("Failed to convert bedrock addr to URL")?,
             auth: None,
         },
+        cross_zone,
     })
 }
 
@@ -201,7 +204,11 @@ pub fn wallet_config(sequencer_addr: SocketAddr) -> Result<WalletConfig> {
     })
 }
 
-pub fn indexer_config(bedrock_addr: SocketAddr) -> Result<IndexerConfig> {
+pub fn indexer_config(
+    bedrock_addr: SocketAddr,
+    channel_id: ChannelId,
+    cross_zone: Option<CrossZoneConfig>,
+) -> Result<IndexerConfig> {
     Ok(IndexerConfig {
         consensus_info_polling_interval: Duration::from_secs(1),
         bedrock_config: ClientConfig {
@@ -209,7 +216,9 @@ pub fn indexer_config(bedrock_addr: SocketAddr) -> Result<IndexerConfig> {
                 .context("Failed to convert bedrock addr to URL")?,
             auth: None,
         },
-        channel_id: bedrock_channel_id(),
+        channel_id,
+        cross_zone,
+        bridge_lock_holdings: Vec::new(),
         allow_chain_reset: false,
     })
 }
@@ -235,3 +244,14 @@ pub fn bedrock_channel_id() -> ChannelId {
         .unwrap_or_else(|_| unreachable!());
     ChannelId::from(channel_id)
 }
+
+/// A second zone's channel id, distinct from [`bedrock_channel_id`] so two zones
+/// settle independently on one shared Bedrock node in the cross-zone tests.
+#[must_use]
+pub fn bedrock_channel_id_b() -> ChannelId {
+    let channel_id: [u8; 32] = [0_u8, 2]
+        .repeat(16)
+        .try_into()
+        .unwrap_or_else(|_| unreachable!());
+    ChannelId::from(channel_id)
+}

test_fixtures/src/lib.rs

@@ -336,9 +336,10 @@ impl TestContextBuilder {
             .context("Failed to setup Bedrock node")?;
 
         let indexer_components = if enable_indexer {
-            let (indexer_handle, temp_indexer_dir) = setup_indexer(bedrock_addr)
-                .await
-                .context("Failed to setup Indexer")?;
+            let (indexer_handle, temp_indexer_dir) =
+                setup_indexer(bedrock_addr, config::bedrock_channel_id(), None)
+                    .await
+                    .context("Failed to setup Indexer")?;
             let indexer_url = config::addr_to_url(config::UrlProtocol::Ws, indexer_handle.addr())
                 .context("Failed to convert indexer addr to URL")?;
             let indexer_client = IndexerClient::new(&indexer_url)
@@ -375,9 +376,15 @@ impl TestContextBuilder {
                 }
                 None => wallet_genesis,
             };
-            setup_sequencer(partial_config, bedrock_addr, genesis)
-                .await
-                .context("Failed to setup Sequencer")?
+            setup_sequencer(
+                partial_config,
+                bedrock_addr,
+                genesis,
+                config::bedrock_channel_id(),
+                None,
+            )
+            .await
+            .context("Failed to setup Sequencer")?
         };
 
         let (mut wallet, temp_wallet_dir, wallet_password) = setup_wallet(

test_fixtures/src/setup.rs

@@ -1,7 +1,7 @@
 use std::{net::SocketAddr, path::PathBuf};
 
 use anyhow::{Context as _, Result, bail};
-use indexer_service::IndexerHandle;
+use indexer_service::{ChannelId, IndexerHandle};
 use lee::{AccountId, PrivateKey, PublicKey};
 use log::{debug, warn};
 use sequencer_core::block_store::{DbDump, SequencerStore};
@@ -112,7 +112,11 @@ pub async fn setup_bedrock_node() -> Result<(DockerCompose, SocketAddr)> {
     Ok((compose, addr))
 }
 
-pub async fn setup_indexer(bedrock_addr: SocketAddr) -> Result<(IndexerHandle, TempDir)> {
+pub async fn setup_indexer(
+    bedrock_addr: SocketAddr,
+    channel_id: ChannelId,
+    cross_zone: Option<sequencer_core::config::CrossZoneConfig>,
+) -> Result<(IndexerHandle, TempDir)> {
     let temp_indexer_dir =
         tempfile::tempdir().context("Failed to create temp dir for indexer home")?;
 
@@ -121,8 +125,8 @@ pub async fn setup_indexer(bedrock_addr: SocketAddr) -> Result<(IndexerHandle, T
         temp_indexer_dir.path().display()
     );
 
-    let indexer_config =
-        config::indexer_config(bedrock_addr).context("Failed to create Indexer config")?;
+    let indexer_config = config::indexer_config(bedrock_addr, channel_id, cross_zone)
+        .context("Failed to create Indexer config")?;
 
     indexer_service::run_server(
         indexer_config,
@@ -139,11 +143,15 @@ pub async fn setup_sequencer(
     partial: config::SequencerPartialConfig,
     bedrock_addr: SocketAddr,
     genesis_transactions: Vec<GenesisAction>,
+    channel_id: ChannelId,
+    cross_zone: Option<sequencer_core::config::CrossZoneConfig>,
 ) -> Result<(SequencerHandle, TempDir)> {
     setup_sequencer_inner(
         partial,
         bedrock_addr,
         SequencerInit::Genesis(genesis_transactions),
+        channel_id,
+        cross_zone,
     )
     .await
 }
@@ -155,13 +163,22 @@ pub async fn setup_sequencer_from_prebuilt(
     bedrock_addr: SocketAddr,
 ) -> Result<(SequencerHandle, TempDir)> {
     let dump = load_prebuilt_dump()?;
-    setup_sequencer_inner(partial, bedrock_addr, SequencerInit::Prebuilt(&dump)).await
+    setup_sequencer_inner(
+        partial,
+        bedrock_addr,
+        SequencerInit::Prebuilt(&dump),
+        config::bedrock_channel_id(),
+        None,
+    )
+    .await
 }
 
 async fn setup_sequencer_inner(
     partial: config::SequencerPartialConfig,
     bedrock_addr: SocketAddr,
     init: SequencerInit<'_>,
+    channel_id: ChannelId,
+    cross_zone: Option<sequencer_core::config::CrossZoneConfig>,
 ) -> Result<(SequencerHandle, TempDir)> {
     let temp_sequencer_dir =
         tempfile::tempdir().context("Failed to create temp dir for sequencer home")?;
@@ -187,6 +204,8 @@ async fn setup_sequencer_inner(
         temp_sequencer_dir.path().to_owned(),
         bedrock_addr,
         genesis_transactions,
+        channel_id,
+        cross_zone,
     )
     .context("Failed to create Sequencer config")?;
 

tools/cross_zone_chat/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "cross_zone_chat"
+version = "0.1.0"
+edition = "2024"
+license = { workspace = true }
+
+[lints]
+workspace = true
+
+[dependencies]
+test_fixtures.workspace = true
+sequencer_service_rpc = { workspace = true, features = ["client"] }
+programs.workspace = true
+ping_core.workspace = true
+cross_zone_outbox_core.workspace = true
+cross_zone_inbox_core.workspace = true
+lee.workspace = true
+common.workspace = true
+risc0-zkvm.workspace = true
+tokio = { workspace = true, features = ["rt-multi-thread", "macros"] }
+anyhow.workspace = true
+serde = { workspace = true, features = ["derive"] }
+axum.workspace = true
+log.workspace = true
+env_logger.workspace = true

tools/cross_zone_chat/src/index.html

@@ -0,0 +1,234 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="utf-8" />
+<meta name="viewport" content="width=device-width, initial-scale=1" />
+<title>Cross-zone chat</title>
+<style>
+  :root { color-scheme: light dark; }
+  * { box-sizing: border-box; }
+  body {
+    margin: 0;
+    font-family: system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
+    background: #0e1116;
+    color: #e6edf3;
+  }
+  header {
+    padding: 14px 20px;
+    border-bottom: 1px solid #232a33;
+    font-size: 15px;
+    color: #9aa7b4;
+  }
+  header b { color: #e6edf3; }
+  .columns { display: flex; height: calc(100vh - 51px); }
+  .zone {
+    flex: 1 1 0;
+    display: flex;
+    flex-direction: column;
+    min-width: 0;
+  }
+  .zone + .zone { border-left: 1px solid #232a33; }
+  .zone h2 {
+    margin: 0;
+    padding: 12px 18px;
+    font-size: 14px;
+    letter-spacing: .04em;
+    text-transform: uppercase;
+    color: #9aa7b4;
+    border-bottom: 1px solid #232a33;
+  }
+  .zone.a h2 { color: #6cb6ff; }
+  .zone.b h2 { color: #6bd968; }
+  .log {
+    flex: 1 1 auto;
+    overflow-y: auto;
+    padding: 14px 18px;
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+  }
+  .msg {
+    background: #161b22;
+    border: 1px solid #232a33;
+    border-radius: 10px;
+    padding: 8px 12px;
+    max-width: 90%;
+    word-wrap: break-word;
+    white-space: pre-wrap;
+  }
+  .msg.inflight { border-color: #3a3320; }
+  .msg .text { margin-bottom: 6px; }
+  .stages {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 6px;
+    font-size: 11px;
+    line-height: 1.4;
+    color: #9aa7b4;
+  }
+  .stage {
+    display: inline-flex;
+    align-items: center;
+    gap: 4px;
+    padding: 1px 7px;
+    border-radius: 999px;
+    border: 1px solid #2d3640;
+    background: #0e1116;
+    white-space: nowrap;
+  }
+  .stage.todo { opacity: .4; }
+  .stage.wait { border-color: #6b5a1f; color: #e3b341; }
+  .stage.done { border-color: #2c5d33; color: #6bd968; }
+  .stage .blk { color: #6cb6ff; font-variant-numeric: tabular-nums; }
+  .elapsed { color: #7d8893; font-variant-numeric: tabular-nums; }
+  .composer {
+    display: flex;
+    gap: 8px;
+    padding: 12px 16px;
+    border-top: 1px solid #232a33;
+  }
+  .composer input {
+    flex: 1 1 auto;
+    padding: 9px 12px;
+    border-radius: 8px;
+    border: 1px solid #2d3640;
+    background: #0e1116;
+    color: #e6edf3;
+    font-size: 14px;
+  }
+  .composer button {
+    padding: 9px 16px;
+    border-radius: 8px;
+    border: 0;
+    background: #2563eb;
+    color: #fff;
+    font-size: 14px;
+    cursor: pointer;
+  }
+  .composer button:disabled { opacity: .5; cursor: default; }
+</style>
+</head>
+<body>
+<header>
+  <b>Cross-zone chat</b> — type in a column; each message shows its journey: sent into a source block, that block reaching <span style="color:#e3b341">Bedrock finality</span>, then <span style="color:#6bd968">delivery</span> into the other zone. The finality wait is the bulk of the latency.
+</header>
+<div class="columns">
+  <section class="zone a" data-zone="A">
+    <h2>Zone A</h2>
+    <div class="log" id="log-A"></div>
+    <form class="composer" data-zone="A">
+      <input type="text" placeholder="Message from Zone A → B" autocomplete="off" />
+      <button type="submit">Send</button>
+    </form>
+  </section>
+  <section class="zone b" data-zone="B">
+    <h2>Zone B</h2>
+    <div class="log" id="log-B"></div>
+    <form class="composer" data-zone="B">
+      <input type="text" placeholder="Message from Zone B → A" autocomplete="off" />
+      <button type="submit">Send</button>
+    </form>
+  </section>
+</div>
+<script>
+  // id -> { el, textEl, stagesEl } for in-place updates.
+  const bubbles = new Map();
+
+  function stage(cls, label, blockZone, block) {
+    const span = '<span class="stage ' + cls + '">' + label +
+      (block != null ? ' <span class="blk">' + blockZone + '#' + block + '</span>' : '') +
+      '</span>';
+    return span;
+  }
+
+  function renderStages(m) {
+    const parts = [];
+    // 1. submitted into a source block on the sender zone
+    if (m.source_block != null) {
+      parts.push(stage('done', 'sent', m.source_zone, m.source_block));
+    } else {
+      parts.push(stage('wait', 'sending…'));
+    }
+    // 2. Bedrock finality of that source block
+    if (m.finalized) {
+      parts.push(stage('done', 'Bedrock ✓ finalized'));
+    } else if (m.source_block != null) {
+      parts.push(stage('wait', 'Bedrock ⏳ pending'));
+    } else {
+      parts.push(stage('todo', 'Bedrock'));
+    }
+    // 3. delivery on the receiver zone
+    if (m.delivered_block != null) {
+      parts.push(stage('done', 'delivered', m.zone, m.delivered_block));
+    } else {
+      parts.push(stage(m.finalized ? 'wait' : 'todo', 'delivering…'));
+    }
+    // elapsed
+    const t = m.delivered_block != null ? (m.elapsed + 's ✓') : (m.elapsed + 's');
+    parts.push('<span class="elapsed">' + t + '</span>');
+    return parts.join('');
+  }
+
+  function upsert(m) {
+    let b = bubbles.get(m.id);
+    if (!b) {
+      const log = document.getElementById('log-' + m.zone);
+      const el = document.createElement('div');
+      el.className = 'msg inflight';
+      const textEl = document.createElement('div');
+      textEl.className = 'text';
+      textEl.textContent = m.text;
+      const stagesEl = document.createElement('div');
+      stagesEl.className = 'stages';
+      el.appendChild(textEl);
+      el.appendChild(stagesEl);
+      log.appendChild(el);
+      log.scrollTop = log.scrollHeight;
+      b = { el, stagesEl };
+      bubbles.set(m.id, b);
+    }
+    b.el.className = 'msg' + (m.delivered_block != null ? '' : ' inflight');
+    b.stagesEl.innerHTML = renderStages(m);
+  }
+
+  async function poll() {
+    try {
+      const res = await fetch('/timeline');
+      if (!res.ok) return;
+      const entries = await res.json();
+      for (const m of entries) upsert(m);
+    } catch (_) { /* transient; retry next tick */ }
+  }
+
+  for (const form of document.querySelectorAll('form.composer')) {
+    form.addEventListener('submit', async (ev) => {
+      ev.preventDefault();
+      const zone = form.dataset.zone;
+      const input = form.querySelector('input');
+      const text = input.value.trim();
+      if (!text) return;
+      input.value = '';
+      try {
+        const res = await fetch('/send', {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify({ zone, text }),
+        });
+        if (!res.ok) {
+          input.value = text;
+          input.placeholder = 'send failed: ' + (await res.text());
+        } else {
+          poll();
+        }
+      } catch (err) {
+        input.value = text;
+        input.placeholder = 'send error: ' + err;
+      }
+    });
+  }
+
+  setInterval(poll, 1000);
+  poll();
+</script>
+</body>
+</html>

tools/cross_zone_chat/src/main.rs

@@ -0,0 +1,533 @@
+//! Interactive cross-zone chat demo.
+//!
+//! Boots one Bedrock node hosting two zones (A and B), each running a sequencer
+//! whose cross-zone watcher points at the other zone, then serves a local
+//! two-column web UI. Type a message in one column and watch it cross Bedrock
+//! and appear in the other; two people can chat across the zones.
+//!
+//! This is the `cross_zone_ping` integration-test topology made interactive:
+//! a send builds a `ping_sender::Send` on the sender zone targeting the other
+//! zone's `ping_receiver`, the other zone's watcher reads the finalized source
+//! block and injects the inbox dispatch, and a per-zone block tailer decodes the
+//! delivered `cross_zone_inbox::Dispatch` payloads back into chat text.
+//!
+//! To make the cross-zone machinery visible, each message is tracked through its
+//! pipeline stages and surfaced to the page: submitted into a source block on the
+//! sender zone, that block's Bedrock finality (pending -> finalized), and final
+//! delivery into a block on the receiver zone. The Bedrock-finality wait is what
+//! dominates the latency, so it is shown live.
+//!
+//! Prerequisite: a working local Docker daemon (Bedrock comes up via
+//! `bedrock/docker-compose.yml`). Run with `RISC0_DEV_MODE=1` for fast,
+//! proving-free latency; on macOS run under the `just cross-zone-chat` recipe so
+//! the DYLD framework shim is set.
+
+#![allow(
+    clippy::arithmetic_side_effects,
+    clippy::print_stdout,
+    clippy::print_stderr,
+    clippy::unused_async,
+    clippy::needless_pass_by_value,
+    clippy::infinite_loop,
+    reason = "Demo binary: stdout banner is the deliverable; ordinal/elapsed arithmetic is \
+              bounded at chat scale; the per-zone scanners and finality poller are daemon \
+              loops that run for the process lifetime; axum handlers must be `async` and take \
+              their extractors (State/Json/Query) by value to satisfy the framework's bounds."
+)]
+
+use std::{
+    collections::BTreeSet,
+    net::SocketAddr,
+    sync::{
+        Arc, Mutex,
+        atomic::{AtomicU32, AtomicU64, Ordering},
+    },
+    time::{Duration, Instant},
+};
+
+use anyhow::{Context as _, Result};
+use axum::{
+    Json, Router,
+    extract::State,
+    http::StatusCode,
+    response::Html,
+    routing::{get, post},
+};
+use common::{block::BedrockStatus, transaction::LeeTransaction};
+use cross_zone_inbox_core::{CrossZoneConfig, CrossZonePeer, Instruction, ZoneId};
+use cross_zone_outbox_core::outbox_pda;
+use lee::{
+    ProgramId, PublicTransaction,
+    public_transaction::{Message, WitnessSet},
+};
+use log::{info, warn};
+use ping_core::{ReceiverInstruction, SenderInstruction, ping_record_pda};
+use sequencer_service_rpc::{RpcClient as _, SequencerClient, SequencerClientBuilder};
+use serde::{Deserialize, Serialize};
+use test_fixtures::{
+    config::{self, SequencerPartialConfig, UrlProtocol, bedrock_channel_id, bedrock_channel_id_b},
+    setup::{setup_bedrock_node, setup_sequencer},
+};
+
+const HTTP_PORT: u16 = 8088;
+const POLL_INTERVAL: Duration = Duration::from_secs(1);
+
+/// One chat message tracked through its cross-zone pipeline. Displayed in the
+/// receiving zone's column; the stage fields drive the on-page timeline.
+struct TrackedMessage {
+    id: u64,
+    /// Label ("A" / "B") of the sender zone.
+    source_label: &'static str,
+    /// Label of the receiver zone; the column this message shows in.
+    dest_label: &'static str,
+    text: String,
+    /// Outbox ordinal of this send, used to match the source-zone block.
+    ordinal: u32,
+    /// Block on the sender zone that included the `ping_sender` tx.
+    source_block: Option<u64>,
+    /// Whether `source_block` has reached Bedrock finality.
+    finalized: bool,
+    /// Block on the receiver zone that delivered the inbox dispatch.
+    delivered_block: Option<u64>,
+    created: Instant,
+    /// Wall-clock seconds from submit to delivery, set once delivered.
+    delivered_secs: Option<u64>,
+}
+
+/// A single send to perform.
+#[derive(Deserialize)]
+struct SendRequest {
+    zone: String,
+    text: String,
+}
+
+/// The id assigned to a freshly submitted message.
+#[derive(Serialize)]
+struct SendResponse {
+    id: u64,
+}
+
+/// One message's current pipeline state, as served to the page.
+#[derive(Serialize)]
+struct TimelineEntry {
+    id: u64,
+    /// Receiver column the message belongs to.
+    zone: &'static str,
+    source_zone: &'static str,
+    text: String,
+    source_block: Option<u64>,
+    finalized: bool,
+    delivered_block: Option<u64>,
+    /// Seconds elapsed (live until delivered, then frozen at delivery time).
+    elapsed: u64,
+}
+
+/// Everything one zone needs to send to its peer.
+struct ZoneRuntime {
+    /// The peer zone's channel id; the target of sends from this zone.
+    other_zone: ZoneId,
+    client: SequencerClient,
+    /// Monotonic outbox ordinal per (this zone -> peer); each send must use a
+    /// fresh value because the outbox PDA is claimed only when default.
+    ordinal: AtomicU32,
+}
+
+struct AppState {
+    zone_a: ZoneRuntime,
+    zone_b: ZoneRuntime,
+    /// Monotonic id assigned to every message.
+    next_id: AtomicU64,
+    messages: Mutex<Vec<TrackedMessage>>,
+}
+
+impl AppState {
+    fn zone(&self, label: &str) -> Option<&ZoneRuntime> {
+        match label {
+            "A" => Some(&self.zone_a),
+            "B" => Some(&self.zone_b),
+            _ => None,
+        }
+    }
+
+    /// Records a freshly submitted outbound message and returns its id.
+    fn record_outbound(
+        &self,
+        source_label: &'static str,
+        dest_label: &'static str,
+        ordinal: u32,
+        text: String,
+    ) -> u64 {
+        let id = self.next_id.fetch_add(1, Ordering::SeqCst);
+        self.messages
+            .lock()
+            .expect("messages mutex poisoned")
+            .push(TrackedMessage {
+                id,
+                source_label,
+                dest_label,
+                text,
+                ordinal,
+                source_block: None,
+                finalized: false,
+                delivered_block: None,
+                created: Instant::now(),
+                delivered_secs: None,
+            });
+        info!("[stage] msg {id} submitted {source_label}->{dest_label}");
+        id
+    }
+
+    /// Marks the source-zone block that included a send, matched by ordinal.
+    fn mark_source_block(&self, source_label: &'static str, ordinal: u32, block_id: u64) {
+        let mut messages = self.messages.lock().expect("messages mutex poisoned");
+        if let Some(message) = messages.iter_mut().find(|m| {
+            m.source_label == source_label && m.ordinal == ordinal && m.source_block.is_none()
+        }) {
+            message.source_block = Some(block_id);
+            info!(
+                "[stage] msg {} in source block {source_label}#{block_id} (+{}s)",
+                message.id,
+                message.created.elapsed().as_secs()
+            );
+        }
+    }
+
+    /// Marks delivery on the receiver zone. Prefers the oldest undelivered
+    /// message whose text matches; falls back to the oldest undelivered for the
+    /// zone (delivery order is preserved end to end).
+    fn mark_delivered(&self, dest_label: &'static str, text: &str, block_id: u64) {
+        let mut messages = self.messages.lock().expect("messages mutex poisoned");
+        let undelivered =
+            |m: &TrackedMessage| m.dest_label == dest_label && m.delivered_block.is_none();
+        let index = messages
+            .iter()
+            .position(|m| undelivered(m) && m.text == text)
+            .or_else(|| messages.iter().position(undelivered));
+        if let Some(index) = index {
+            let message = &mut messages[index];
+            message.delivered_block = Some(block_id);
+            let secs = message.created.elapsed().as_secs();
+            message.delivered_secs = Some(secs);
+            info!(
+                "[stage] msg {} delivered {dest_label}#{block_id} (+{secs}s total)",
+                message.id
+            );
+        }
+    }
+
+    /// Snapshot of (source zone, block) pairs whose finality is still unknown.
+    fn pending_finality(&self) -> BTreeSet<(&'static str, u64)> {
+        self.messages
+            .lock()
+            .expect("messages mutex poisoned")
+            .iter()
+            .filter(|m| !m.finalized)
+            .filter_map(|m| m.source_block.map(|block| (m.source_label, block)))
+            .collect()
+    }
+
+    /// Marks every message whose source block has reached Bedrock finality.
+    fn mark_finalized(&self, source_label: &'static str, block_id: u64) {
+        for message in self
+            .messages
+            .lock()
+            .expect("messages mutex poisoned")
+            .iter_mut()
+        {
+            if message.source_label == source_label
+                && message.source_block == Some(block_id)
+                && !message.finalized
+            {
+                message.finalized = true;
+                info!(
+                    "[stage] msg {} source block {source_label}#{block_id} finalized on Bedrock (+{}s)",
+                    message.id,
+                    message.created.elapsed().as_secs()
+                );
+            }
+        }
+    }
+
+    fn timeline(&self) -> Vec<TimelineEntry> {
+        self.messages
+            .lock()
+            .expect("messages mutex poisoned")
+            .iter()
+            .map(|m| TimelineEntry {
+                id: m.id,
+                zone: m.dest_label,
+                source_zone: m.source_label,
+                text: m.text.clone(),
+                source_block: m.source_block,
+                finalized: m.finalized,
+                delivered_block: m.delivered_block,
+                elapsed: m
+                    .delivered_secs
+                    .unwrap_or_else(|| m.created.elapsed().as_secs()),
+            })
+            .collect()
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    env_logger::init();
+
+    // Declared first so Bedrock outlives both zones (drops run in reverse order).
+    let (_bedrock, bedrock_addr) = setup_bedrock_node()
+        .await
+        .context("Failed to set up shared Bedrock node")?;
+
+    let channel_a = bedrock_channel_id();
+    let channel_b = bedrock_channel_id_b();
+    let zone_a: ZoneId = *channel_a.as_ref();
+    let zone_b: ZoneId = *channel_b.as_ref();
+    let receiver_id = programs::ping_receiver().id();
+
+    // Each zone watches the other and may deliver only to ping_receiver.
+    let cross_zone_a = watch_peer(zone_b, receiver_id);
+    let cross_zone_b = watch_peer(zone_a, receiver_id);
+
+    let partial = SequencerPartialConfig::default();
+    let (seq_a, _home_a) =
+        setup_sequencer(partial, bedrock_addr, vec![], channel_a, Some(cross_zone_a))
+            .await
+            .context("Failed to set up zone A sequencer")?;
+    let (seq_b, _home_b) =
+        setup_sequencer(partial, bedrock_addr, vec![], channel_b, Some(cross_zone_b))
+            .await
+            .context("Failed to set up zone B sequencer")?;
+
+    let state = Arc::new(AppState {
+        zone_a: ZoneRuntime {
+            other_zone: zone_b,
+            client: sequencer_client(seq_a.addr())?,
+            ordinal: AtomicU32::new(0),
+        },
+        zone_b: ZoneRuntime {
+            other_zone: zone_a,
+            client: sequencer_client(seq_b.addr())?,
+            ordinal: AtomicU32::new(0),
+        },
+        next_id: AtomicU64::new(1),
+        messages: Mutex::new(Vec::new()),
+    });
+
+    tokio::spawn(scan_zone(Arc::clone(&state), "A"));
+    tokio::spawn(scan_zone(Arc::clone(&state), "B"));
+    tokio::spawn(poll_finality(Arc::clone(&state)));
+
+    let app = Router::new()
+        .route("/", get(index))
+        .route("/send", post(send_handler))
+        .route("/timeline", get(timeline_handler))
+        .with_state(state);
+
+    let addr = SocketAddr::from(([127, 0, 0, 1], HTTP_PORT));
+    let listener = tokio::net::TcpListener::bind(addr)
+        .await
+        .with_context(|| format!("Failed to bind {addr}"))?;
+
+    println!("\n  💬 Cross-zone chat ready — open http://127.0.0.1:{HTTP_PORT} in your browser\n");
+
+    axum::serve(listener, app)
+        .await
+        .context("HTTP server error")?;
+    Ok(())
+}
+
+/// A cross-zone config whose single peer is `peer`, allowed to deliver only to
+/// `receiver_id`.
+fn watch_peer(peer: ZoneId, receiver_id: ProgramId) -> CrossZoneConfig {
+    CrossZoneConfig {
+        peers: vec![CrossZonePeer {
+            channel_id: peer,
+            allowed_targets: vec![receiver_id],
+            expected_block_signing_pubkey: None,
+        }],
+    }
+}
+
+fn sequencer_client(addr: SocketAddr) -> Result<SequencerClient> {
+    let url =
+        config::addr_to_url(UrlProtocol::Http, addr).context("Failed to build sequencer URL")?;
+    SequencerClientBuilder::default()
+        .build(url)
+        .context("Failed to build sequencer client")
+}
+
+/// Scans one zone's new blocks. A `ping_sender` tx marks the message's source
+/// block (its outbound leg); an inbox dispatch marks delivery on this zone.
+/// Runs forever; transient RPC errors are logged and retried.
+async fn scan_zone(state: Arc<AppState>, label: &'static str) {
+    let inbox_id = programs::cross_zone_inbox().id();
+    let sender_id = programs::ping_sender().id();
+    let client = &state.zone(label).expect("zone runtime exists").client;
+
+    // Start from the current tip so genesis/boot blocks are skipped.
+    let mut cursor = client.get_last_block_id().await.unwrap_or(0);
+
+    loop {
+        tokio::time::sleep(POLL_INTERVAL).await;
+
+        let last = match client.get_last_block_id().await {
+            Ok(last) => last,
+            Err(err) => {
+                warn!("[{label}] get_last_block_id failed: {err:#}");
+                continue;
+            }
+        };
+
+        while cursor < last {
+            let next = cursor.saturating_add(1);
+            match client.get_block(next).await {
+                Ok(Some(block)) => {
+                    for tx in &block.body.transactions {
+                        let LeeTransaction::Public(public) = tx else {
+                            continue;
+                        };
+                        let program_id = public.message.program_id;
+                        let data = &public.message.instruction_data;
+                        // A tx targets at most one of these programs; check both
+                        // independently rather than chaining (avoids an empty else).
+                        if program_id == inbox_id
+                            && let Some(text) = decode_inbox_text(data)
+                        {
+                            state.mark_delivered(label, &text, next);
+                        }
+                        if program_id == sender_id
+                            && let Some(ordinal) = decode_send_ordinal(data)
+                        {
+                            state.mark_source_block(label, ordinal, next);
+                        }
+                    }
+                }
+                Ok(None) => {}
+                Err(err) => {
+                    warn!("[{label}] get_block({next}) failed: {err:#}");
+                    break;
+                }
+            }
+            cursor = next;
+        }
+    }
+}
+
+/// Polls each tracked source block's Bedrock finality until it is finalized.
+async fn poll_finality(state: Arc<AppState>) {
+    loop {
+        tokio::time::sleep(POLL_INTERVAL).await;
+        for (label, block_id) in state.pending_finality() {
+            let client = &state.zone(label).expect("zone runtime exists").client;
+            match client.get_block(block_id).await {
+                Ok(Some(block)) => {
+                    if matches!(block.bedrock_status, BedrockStatus::Finalized) {
+                        state.mark_finalized(label, block_id);
+                    }
+                }
+                Ok(None) => {}
+                Err(err) => warn!("[{label}] finality get_block({block_id}) failed: {err:#}"),
+            }
+        }
+    }
+}
+
+/// Recovers the chat text from an inbox dispatch tx's instruction data.
+fn decode_inbox_text(instruction_data: &[u32]) -> Option<String> {
+    let instruction: Instruction =
+        risc0_zkvm::serde::from_slice::<Instruction, u32>(instruction_data).ok()?;
+    let Instruction::Dispatch(message) = instruction;
+    decode_payload(&message.payload)
+}
+
+/// Recovers the outbox ordinal from a `ping_sender::Send` tx's instruction data.
+fn decode_send_ordinal(instruction_data: &[u32]) -> Option<u32> {
+    let instruction: SenderInstruction =
+        risc0_zkvm::serde::from_slice::<SenderInstruction, u32>(instruction_data).ok()?;
+    let SenderInstruction::Send { ordinal, .. } = instruction;
+    Some(ordinal)
+}
+
+/// Decodes a `ping_receiver::Record` payload (risc0 words in LE bytes) to text.
+fn decode_payload(payload: &[u8]) -> Option<String> {
+    let chunks = payload.chunks_exact(4);
+    if !chunks.remainder().is_empty() {
+        return None;
+    }
+    let words: Vec<u32> = chunks
+        .map(|chunk| u32::from_le_bytes(chunk.try_into().expect("chunks_exact(4) yields 4 bytes")))
+        .collect();
+    let instruction: ReceiverInstruction =
+        risc0_zkvm::serde::from_slice::<ReceiverInstruction, u32>(&words).ok()?;
+    let ReceiverInstruction::Record { payload: bytes } = instruction;
+    Some(String::from_utf8_lossy(&bytes).into_owned())
+}
+
+/// Builds the unsigned `ping_sender::Send` that carries `text` to `other_zone`,
+/// mirroring `integration_tests/tests/cross_zone_ping.rs`.
+fn build_send_tx(other_zone: ZoneId, ordinal: u32, text: &str) -> LeeTransaction {
+    let receiver_id = programs::ping_receiver().id();
+    let outbox_id = programs::cross_zone_outbox().id();
+
+    let words = risc0_zkvm::serde::to_vec(&ReceiverInstruction::Record {
+        payload: text.as_bytes().to_vec(),
+    })
+    .expect("serialize record instruction");
+    let payload: Vec<u8> = words.iter().flat_map(|word| word.to_le_bytes()).collect();
+
+    let send = SenderInstruction::Send {
+        outbox_program_id: outbox_id,
+        target_zone: other_zone,
+        target_program_id: receiver_id,
+        target_accounts: vec![ping_record_pda(receiver_id).into_value()],
+        payload,
+        ordinal,
+    };
+
+    let outbox_account = outbox_pda(outbox_id, &other_zone, ordinal);
+    let message = Message::try_new(
+        programs::ping_sender().id(),
+        vec![outbox_account],
+        vec![],
+        send,
+    )
+    .expect("build ping_sender message");
+
+    LeeTransaction::Public(PublicTransaction::new(
+        message,
+        WitnessSet::from_raw_parts(vec![]),
+    ))
+}
+
+async fn index() -> Html<&'static str> {
+    Html(include_str!("index.html"))
+}
+
+async fn send_handler(
+    State(state): State<Arc<AppState>>,
+    Json(request): Json<SendRequest>,
+) -> Result<Json<SendResponse>, (StatusCode, String)> {
+    let text = request.text.trim();
+    if text.is_empty() {
+        return Err((StatusCode::BAD_REQUEST, "empty message".to_owned()));
+    }
+    let (source_label, dest_label) = match request.zone.as_str() {
+        "A" => ("A", "B"),
+        "B" => ("B", "A"),
+        other => return Err((StatusCode::BAD_REQUEST, format!("unknown zone {other}"))),
+    };
+    let zone = state.zone(source_label).expect("zone runtime exists");
+
+    let ordinal = zone.ordinal.fetch_add(1, Ordering::SeqCst);
+    let tx = build_send_tx(zone.other_zone, ordinal, text);
+    let id = state.record_outbound(source_label, dest_label, ordinal, text.to_owned());
+    zone.client
+        .send_transaction(tx)
+        .await
+        .map_err(|err| (StatusCode::BAD_GATEWAY, format!("submit failed: {err:#}")))?;
+    Ok(Json(SendResponse { id }))
+}
+
+async fn timeline_handler(State(state): State<Arc<AppState>>) -> Json<Vec<TimelineEntry>> {
+    Json(state.timeline())
+}