diff --git a/crates/buzz-acp/src/lib.rs b/crates/buzz-acp/src/lib.rs
index 600f0499d6..a4bfe4574f 100644
--- a/crates/buzz-acp/src/lib.rs
+++ b/crates/buzz-acp/src/lib.rs
@@ -14,6 +14,8 @@ mod observer;
 mod pool;
 mod pool_lifecycle;
 #[cfg(all(test, unix))]
+mod pool_refill_tests;
+#[cfg(all(test, unix))]
 mod pool_startup_tests;
 mod prompt_framing;
 mod prompt_project;
diff --git a/crates/buzz-acp/src/pool_refill_tests.rs b/crates/buzz-acp/src/pool_refill_tests.rs
new file mode 100644
index 0000000000..3d5019e221
--- /dev/null
+++ b/crates/buzz-acp/src/pool_refill_tests.rs
@@ -0,0 +1,235 @@
+//! Exercise immediate refill through the full harness, a local relay and real workers.
+use super::*;
+use axum::{
+    extract::{ws::WebSocketUpgrade, State},
+    response::IntoResponse,
+    routing::{get, post},
+    Json, Router,
+};
+use serde_json::{json, Value};
+
+struct RelayFixture {
+    channels: Vec<Uuid>,
+    pubkey: String,
+    events: tokio::sync::Mutex<mpsc::UnboundedReceiver<Vec<nostr::Event>>>,
+}
+
+async fn relay_socket(
+    State(state): State<Arc<RelayFixture>>,
+    upgrade: Result<WebSocketUpgrade, axum::extract::ws::rejection::WebSocketUpgradeRejection>,
+) -> axum::response::Response {
+    let Ok(upgrade) = upgrade else {
+        return Json(json!({"pubkey": state.pubkey})).into_response();
+    };
+    upgrade.on_upgrade(move |mut socket| async move {
+        use axum::extract::ws::Message;
+        let mut events = state.events.lock().await;
+        socket.send(Message::Text(json!(["AUTH", "fixture"]).to_string().into())).await.unwrap();
+        loop {
+            tokio::select! {
+                message = socket.recv() => {
+                    let Some(Ok(Message::Text(text))) = message else { break };
+                    let message: Value = serde_json::from_str(&text).unwrap();
+                    let reply = match message[0].as_str() {
+                        Some("AUTH" | "EVENT") => Some(json!(["OK", message[1]["id"], true, ""])),
+                        Some("REQ") => Some(json!(["EOSE", message[1]])),
+                        _ => None,
+                    };
+                    if let Some(reply) = reply {
+                        if socket.send(Message::Text(reply.to_string().into())).await.is_err() { break }
+                    }
+                }
+                batch = events.recv() => {
+                    let Some(batch) = batch else { break };
+                    for (channel, event) in state.channels.iter().zip(batch) {
+                        let message = json!(["EVENT", format!("ch-{channel}"), event]);
+                        if socket.send(Message::Text(message.to_string().into())).await.is_err() { return }
+                    }
+                }
+            }
+        }
+    })
+}
+
+async fn relay_query(
+    State(state): State<Arc<RelayFixture>>,
+    Json(filters): Json<Value>,
+) -> Json<Value> {
+    let events: Vec<Value> = match filters[0]["kinds"][0].as_u64() {
+        Some(39002) => state
+            .channels
+            .iter()
+            .map(|id| json!({"tags": [["d", id]]}))
+            .collect(),
+        Some(39000) => state
+            .channels
+            .iter()
+            .map(|id| json!({"tags": [["d", id], ["name", "refill"], ["t", "stream"]]}))
+            .collect(),
+        _ => vec![],
+    };
+    Json(json!(events))
+}
+
+fn worker_pids(path: &std::path::Path, prefix: &str) -> Vec<i32> {
+    std::fs::read_dir(path)
+        .unwrap()
+        .filter_map(|entry| {
+            entry
+                .unwrap()
+                .file_name()
+                .to_str()?
+                .strip_prefix(prefix)?
+                .parse()
+                .ok()
+        })
+        .collect()
+}
+
+async fn wait_for_prompts(path: &std::path::Path, count: usize) {
+    while worker_pids(path, "prompt-").len() < count {
+        tokio::time::sleep(Duration::from_millis(10)).await;
+    }
+}
+
+async fn immediate_refill(lazy: bool) {
+    let temp = tempfile::tempdir().unwrap();
+    let script = temp.path().join("adapter.py");
+    let release = temp.path().join("release");
+    std::fs::write(
+        &script,
+        r#"import json, os, pathlib, sys, time
+root = pathlib.Path(os.environ['PROBE_DIR'])
+(root / ('launch-' + str(os.getpid()))).touch()
+for line in sys.stdin:
+    message = json.loads(line)
+    method = message.get('method')
+    if method == 'initialize':
+        result = {'protocolVersion': 1, 'agentInfo': {'name': 'refill-probe'}}
+    elif method == 'session/new':
+        result = {'sessionId': str(os.getpid())}
+    elif method == 'session/prompt':
+        (root / ('prompt-' + str(os.getpid()))).touch()
+        while not (root / 'release').exists():
+            time.sleep(0.01)
+        result = {'stopReason': 'end_turn'}
+    else:
+        result = {}
+    if 'id' in message:
+        print(json.dumps({'jsonrpc': '2.0', 'id': message['id'], 'result': result}), flush=True)
+"#,
+    )
+    .unwrap();
+
+    let (events_tx, events_rx) = mpsc::unbounded_channel();
+    let channels: Vec<_> = (0..3).map(|_| Uuid::new_v4()).collect();
+    let author = nostr::Keys::generate();
+    let state = Arc::new(RelayFixture {
+        channels: channels.clone(),
+        pubkey: author.public_key().to_hex(),
+        events: tokio::sync::Mutex::new(events_rx),
+    });
+    let app = Router::new()
+        .route("/", get(relay_socket))
+        .route("/query", post(relay_query))
+        .with_state(state);
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let address = listener.local_addr().unwrap();
+    let server = tokio::spawn(async move { axum::serve(listener, app).await.unwrap() });
+    let mut config = build_mcp_servers_tests::test_config();
+    config.relay_url = format!("ws://{address}");
+    config.agent_command = "python3".into();
+    config.agent_args = vec![script.to_str().unwrap().into()];
+    config.persona_env_vars = vec![("PROBE_DIR".into(), temp.path().to_str().unwrap().into())];
+    config.agents = 3;
+    config.lazy_pool = lazy;
+    config.idle_pool_sleep_secs = if lazy { 1 } else { 0 };
+    config.presence_enabled = false;
+    config.typing_enabled = false;
+    config.no_base_prompt = true;
+    config.context_message_limit = 0;
+    let (shutdown_tx, shutdown_rx) = watch::channel(());
+    let (ready_tx, ready_rx) = tokio::sync::oneshot::channel();
+    let mut harness = tokio::task::JoinSet::new();
+    harness.spawn(run_harness(
+        config,
+        shutdown_tx.clone(),
+        shutdown_rx,
+        ready_tx,
+    ));
+
+    let outcome = tokio::time::timeout(
+        Duration::from_secs(15),
+        std::panic::AssertUnwindSafe(async {
+            ready_rx.await.unwrap();
+            if lazy {
+                assert!(worker_pids(temp.path(), "launch-").is_empty());
+            }
+            for round in 0..if lazy { 2 } else { 1 } {
+                let events = channels
+                    .iter()
+                    .map(|channel| {
+                        nostr::EventBuilder::new(nostr::Kind::Custom(9), format!("round {round}"))
+                            .tags([
+                                nostr::Tag::parse(["h".to_owned(), channel.to_string()]).unwrap()
+                            ])
+                            .sign_with_keys(&author)
+                            .unwrap()
+                    })
+                    .collect();
+                events_tx.send(events).unwrap();
+                tokio::time::timeout(
+                    Duration::from_secs(5),
+                    wait_for_prompts(temp.path(), (round + 1) * 3),
+                )
+                .await
+                .unwrap_or_else(|_| {
+                    panic!(
+                        "round {round}: expected {} prompt workers before the 30s maintenance delay, got {}",
+                        (round + 1) * 3,
+                        worker_pids(temp.path(), "prompt-").len()
+                    )
+                });
+                assert_eq!(worker_pids(temp.path(), "launch-").len(), (round + 1) * 3);
+                std::fs::write(&release, "done").unwrap();
+                if lazy && round == 0 {
+                    // A second wake is essential: the first lazy wake inherits the
+                    // eager backdate, whereas this one follows recent maintenance.
+                    use nix::{sys::signal::kill, unistd::Pid};
+                    let pids = worker_pids(temp.path(), "launch-");
+                    while pids
+                        .iter()
+                        .any(|pid| kill(Pid::from_raw(*pid), None).is_ok())
+                    {
+                        tokio::time::sleep(Duration::from_millis(10)).await;
+                    }
+                    std::fs::remove_file(&release).unwrap();
+                }
+            }
+        })
+        .catch_unwind(),
+    )
+    .await;
+    // Release prompts and exercise production shutdown even on a failed deadline.
+    std::fs::write(&release, "done").unwrap();
+    let _ = shutdown_tx.send(());
+    let stopped = tokio::time::timeout(Duration::from_secs(6), harness.join_next()).await;
+    if stopped.is_err() {
+        harness.shutdown().await;
+    }
+    server.abort();
+    outcome
+        .expect("harness refill scenario exceeded its deadline")
+        .expect("harness refill scenario failed");
+    stopped.unwrap().unwrap().unwrap().unwrap();
+}
+
+#[tokio::test]
+async fn eager_pool_refills_immediately_through_harness_maintenance() {
+    immediate_refill(false).await;
+}
+
+#[tokio::test]
+async fn lazy_pool_refills_immediately_after_sleep_and_wake() {
+    immediate_refill(true).await;
+}
diff --git a/crates/buzz-acp/src/pool_startup_tests.rs b/crates/buzz-acp/src/pool_startup_tests.rs
index e5ef2881f2..45e2d1c964 100644
--- a/crates/buzz-acp/src/pool_startup_tests.rs
+++ b/crates/buzz-acp/src/pool_startup_tests.rs
@@ -42,7 +42,7 @@ for line in sys.stdin:
     assert_eq!(
         remaining,
         (true, true),
-        "refill retains configured capacity"
+        "startup preserves the slots for background refill"
     );
 }