diff --git a/.config/nextest.toml b/.config/nextest.toml
index 79608e2ff..c02287239 100644
--- a/.config/nextest.toml
+++ b/.config/nextest.toml
@@ -54,3 +54,19 @@ default-filter = """
     not test(testnet)
     & not test(client_rpcs)
 """
+
+# Debug profile for hunting hangs and load-dependent flakes in the production
+# unit tests, which the default profile deliberately runs without any
+# slow-timeout. A parallel run under this profile names laggards with a SLOW
+# line at 60s and terminates a genuinely stuck test at 300s, dumping its
+# captured output — run with RUST_LOG=trace so that capture holds the full
+# instrumentation:
+#
+#   NEXTEST_PROFILE=hangdebug RUST_LOG=trace cargo nextest run
+#
+[profile.hangdebug]
+fail-fast = false
+
+[[profile.hangdebug.overrides]]
+filter = 'package(zaino-state)'
+slow-timeout = { period = "60s", terminate-after = "5" }
diff --git a/packages/zaino-state/src/chain_index/tests/mockchain_tests.rs b/packages/zaino-state/src/chain_index/tests/mockchain_tests.rs
index 2ee2de790..86ffba684 100644
--- a/packages/zaino-state/src/chain_index/tests/mockchain_tests.rs
+++ b/packages/zaino-state/src/chain_index/tests/mockchain_tests.rs
@@ -11,7 +11,7 @@ use crate::{
     },
     BlockchainSource as _, Outpoint,
 };
-use tokio::time::{sleep, Duration};
+use tokio::time::Duration;
 use tokio_stream::StreamExt as _;
 use zaino_fetch::jsonrpsee::response::address_deltas::{
     GetAddressDeltasParams, GetAddressDeltasResponse,
@@ -423,10 +423,20 @@ async fn get_mempool_stream_no_expected_chain_tip_snapshot() {
         .unwrap_or_default();
     mempool_transactions.sort_by_key(|transaction| transaction.hash());
 
+    // Same ordering constraint as the expected-tip variant below: the stream
+    // must open before the mine, or it observes the drained post-mine
+    // mempool and collects nothing. Without an expected tip there is no
+    // guard at open, so the lost race presents as an assertion failure
+    // rather than a hang. The handshake makes the ordering deterministic.
+    let (stream_opened_tx, stream_opened_rx) = tokio::sync::oneshot::channel();
+
     let mempool_stream_task = tokio::spawn(async move {
         let mut mempool_stream = index_reader
             .get_mempool_stream(None)
             .expect("failed to create mempool stream");
+        stream_opened_tx
+            .send(())
+            .expect("the main task awaits the handshake");
 
         let mut indexer_mempool_transactions: Vec<zebra_chain::transaction::Transaction> =
             Vec::new();
@@ -442,7 +452,9 @@ async fn get_mempool_stream_no_expected_chain_tip_snapshot() {
         indexer_mempool_transactions
     });
 
-    sleep(Duration::from_millis(500)).await;
+    stream_opened_rx
+        .await
+        .expect("the collector task opens the stream");
 
     mockchain.mine_blocks(1);
 
@@ -484,11 +496,22 @@ async fn get_mempool_stream_correct_expected_chain_tip_snapshot() {
         .unwrap_or_default();
     mempool_transactions.sort_by_key(|transaction| transaction.hash());
 
+    // The stream closes only when the chain tip moves away from the tip its
+    // snapshot recorded, and the mine below is that one move: the snapshot
+    // and stream-open must therefore happen strictly before the mine, or the
+    // stream arms itself against the post-mine tip and waits forever for a
+    // second mine that never comes. A handshake makes the ordering
+    // deterministic where a sleep only made it likely on an idle machine.
+    let (stream_opened_tx, stream_opened_rx) = tokio::sync::oneshot::channel();
+
     let mempool_stream_task = tokio::spawn(async move {
         let nonfinalized_snapshot = index_reader.snapshot_nonfinalized_state().await.unwrap();
         let mut mempool_stream = index_reader
             .get_mempool_stream(Some(&nonfinalized_snapshot))
             .expect("failed to create mempool stream");
+        stream_opened_tx
+            .send(())
+            .expect("the main task awaits the handshake");
 
         let mut indexer_mempool_transactions: Vec<zebra_chain::transaction::Transaction> =
             Vec::new();
@@ -504,7 +527,9 @@ async fn get_mempool_stream_correct_expected_chain_tip_snapshot() {
         indexer_mempool_transactions
     });
 
-    sleep(Duration::from_millis(500)).await;
+    stream_opened_rx
+        .await
+        .expect("the collector task opens the stream");
 
     mockchain.mine_blocks(1);