diff --git a/crates/obscura-cdp/tests/concurrent_connections_heavy_page.rs b/crates/obscura-cdp/tests/concurrent_connections_heavy_page.rs
new file mode 100644
index 0000000..e2e51a3
--- /dev/null
+++ b/crates/obscura-cdp/tests/concurrent_connections_heavy_page.rs
@@ -0,0 +1,245 @@
+//! Issue #430 regression: concurrent CDP connections driving a subresource-heavy
+//! page must not abort the process.
+//!
+//! Why this and not `concurrent_navigations` (data: URLs): the #430 abort needs
+//! a page whose event loop is still busy when the navigation settle loop's
+//! per-tick `tokio::time::timeout` around `run_event_loop` fires. A cancelled
+//! `run_event_loop` future left an isolate entered on the shared LocalSet
+//! thread; a second connection's `execute_script` then tripped V8's
+//! `heap->isolate() == Isolate::TryGetCurrent()` check and `abort(3)`'d. `data:`
+//! URLs settle instantly (no subresources, no busy loop), so they never drive
+//! it. This test serves a local page with SLOW subresources plus a `setInterval`
+//! so the settle loop keeps pumping, then drives it from several independent
+//! connections at once.
+//!
+//! On the single-LocalSet server this aborted deterministically. The
+//! thread-per-connection server confines each connection's isolates to their own
+//! OS thread, so the abort cannot happen (V8's check is per-thread) and all
+//! clients complete.
+//!
+//! Run with `cargo test -p obscura-cdp --test concurrent_connections_heavy_page
+//! -- --nocapture`.
+
+use std::time::Duration;
+
+use futures_util::{SinkExt, StreamExt};
+use serde_json::{json, Value};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpListener;
+use tokio_tungstenite::{connect_async, tungstenite::Message};
+
+const CLIENTS: u64 = 4;
+
+async fn pick_port() -> u16 {
+    let l = TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let port = l.local_addr().unwrap().port();
+    drop(l);
+    port
+}
+
+/// Minimal HTTP fixture: a root page with two subresources that respond after a
+/// delay (keeping the navigation settle loop pumping) and an inline
+/// `setInterval` that keeps the event loop non-idle. Serves every connection it
+/// accepts until the test ends.
+async fn serve_heavy_fixture(listener: TcpListener) {
+    let body = "<!DOCTYPE html><html><head>\
+        <script src=\"/slow.js\"></script>\
+        </head><body><h1>heavy</h1><img src=\"/slow.png\">\
+        <script>setInterval(function(){var x=0;for(var i=0;i<2000;i++){x+=i;}}, 3);</script>\
+        </body></html>";
+    loop {
+        let (mut sock, _) = match listener.accept().await {
+            Ok(s) => s,
+            Err(_) => return,
+        };
+        tokio::task::spawn_local(async move {
+            let mut buf = [0u8; 2048];
+            let n = sock.read(&mut buf).await.unwrap_or(0);
+            if n == 0 {
+                return;
+            }
+            let req = String::from_utf8_lossy(&buf[..n]);
+            let path = req
+                .split_whitespace()
+                .nth(1)
+                .unwrap_or("/")
+                .to_string();
+
+            // Slow subresources: respond after a delay so `active_requests` stays
+            // > 0 through several 10ms settle ticks, which is what forces the
+            // per-tick timeout to cancel `run_event_loop` mid-poll on the old
+            // single-thread server.
+            let (ctype, payload): (&str, Vec<u8>) = if path == "/slow.js" {
+                tokio::time::sleep(Duration::from_millis(120)).await;
+                ("application/javascript", b"void 0;".to_vec())
+            } else if path == "/slow.png" {
+                tokio::time::sleep(Duration::from_millis(120)).await;
+                // 1x1 transparent PNG.
+                (
+                    "image/png",
+                    vec![
+                        0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00, 0x0d,
+                        0x49, 0x48, 0x44, 0x52, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01,
+                        0x08, 0x06, 0x00, 0x00, 0x00, 0x1f, 0x15, 0xc4, 0x89, 0x00, 0x00, 0x00,
+                        0x0a, 0x49, 0x44, 0x41, 0x54, 0x78, 0x9c, 0x63, 0x00, 0x01, 0x00, 0x00,
+                        0x05, 0x00, 0x01, 0x0d, 0x0a, 0x2d, 0xb4, 0x00, 0x00, 0x00, 0x00, 0x49,
+                        0x45, 0x4e, 0x44, 0xae, 0x42, 0x60, 0x82,
+                    ],
+                )
+            } else {
+                ("text/html", body.as_bytes().to_vec())
+            };
+
+            let header = format!(
+                "HTTP/1.1 200 OK\r\nContent-Type: {}\r\nContent-Length: {}\r\nConnection: close\r\n\r\n",
+                ctype,
+                payload.len()
+            );
+            let _ = sock.write_all(header.as_bytes()).await;
+            let _ = sock.write_all(&payload).await;
+            let _ = sock.flush().await;
+        });
+    }
+}
+
+/// One client: open its own CDP connection, create a target at the heavy page,
+/// navigate, then repeatedly `Runtime.evaluate` an awaited promise. Returns Err
+/// on protocol failure; a V8 abort would take the whole process down instead.
+async fn one_client(ws_port: u16, page_url: String, id_base: u64) -> Result<(), String> {
+    let url = format!("ws://127.0.0.1:{}/devtools/browser", ws_port);
+    let (mut ws, _) = connect_async(&url).await.map_err(|e| e.to_string())?;
+
+    let create = json!({
+        "id": id_base,
+        "method": "Target.createTarget",
+        "params": {"url": page_url},
+    });
+    ws.send(Message::Text(create.to_string().into()))
+        .await
+        .map_err(|e| e.to_string())?;
+
+    let mut session_id: Option<String> = None;
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(20);
+    while session_id.is_none() {
+        if tokio::time::Instant::now() >= deadline {
+            return Err("timeout waiting for sessionId".to_string());
+        }
+        let msg = tokio::time::timeout(Duration::from_secs(10), ws.next())
+            .await
+            .map_err(|_| "timeout waiting for createTarget".to_string())?
+            .ok_or("ws closed")?
+            .map_err(|e| e.to_string())?;
+        let text = match msg {
+            Message::Text(t) => t.to_string(),
+            _ => continue,
+        };
+        let v: Value = serde_json::from_str(&text).map_err(|e| e.to_string())?;
+        if let Some(s) = v
+            .get("params")
+            .and_then(|p| p.get("sessionId"))
+            .and_then(|s| s.as_str())
+        {
+            session_id = Some(s.to_string());
+        }
+    }
+    let sid = session_id.unwrap();
+
+    // A few awaited evaluations: each drives resolve_promises_until while the
+    // page's setInterval keeps the loop busy — the settle/eval cancellation path.
+    for k in 0..3u64 {
+        let eval = json!({
+            "id": id_base + 100 + k,
+            "method": "Runtime.evaluate",
+            "sessionId": sid,
+            "params": {
+                "expression": "new Promise(r => setTimeout(() => r(1 + 1), 40))",
+                "awaitPromise": true,
+                "returnByValue": true,
+            },
+        });
+        ws.send(Message::Text(eval.to_string().into()))
+            .await
+            .map_err(|e| e.to_string())?;
+
+        let d = tokio::time::Instant::now() + Duration::from_secs(15);
+        loop {
+            if tokio::time::Instant::now() >= d {
+                return Err(format!("timeout waiting for evaluate {}", k));
+            }
+            let remaining = d - tokio::time::Instant::now();
+            let msg = tokio::time::timeout(remaining, ws.next())
+                .await
+                .map_err(|_| "timeout".to_string())?
+                .ok_or("ws closed mid-evaluate")?
+                .map_err(|e| e.to_string())?;
+            let text = match msg {
+                Message::Text(t) => t.to_string(),
+                _ => continue,
+            };
+            let v: Value = serde_json::from_str(&text).map_err(|e| e.to_string())?;
+            if v.get("id").and_then(|x| x.as_u64()) == Some(id_base + 100 + k) {
+                break;
+            }
+        }
+    }
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "current_thread")]
+async fn concurrent_connections_heavy_page_do_not_abort_v8() {
+    let ws_port = pick_port().await;
+    // Bind the fixture listener up front so we can hand its port to the clients.
+    let fixture = TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let fixture_port = fixture.local_addr().unwrap().port();
+    let page_url = format!("http://127.0.0.1:{}/", fixture_port);
+
+    let local = tokio::task::LocalSet::new();
+    local
+        .run_until(async {
+            // Fixture HTTP server.
+            tokio::task::spawn_local(serve_heavy_fixture(fixture));
+
+            // CDP server. allow_private_network so it may fetch 127.0.0.1.
+            tokio::task::spawn_local(async move {
+                let _ = obscura_cdp::server::start_with_full_serve_options(
+                    ws_port,
+                    "127.0.0.1",
+                    None,
+                    false,
+                    None,
+                    false,
+                    None,
+                    true,
+                )
+                .await;
+            });
+            tokio::time::sleep(Duration::from_millis(200)).await;
+
+            let mut handles = Vec::new();
+            for i in 0..CLIENTS {
+                let url = page_url.clone();
+                let id_base = (i + 1) * 1000;
+                handles.push(tokio::task::spawn_local(async move {
+                    one_client(ws_port, url, id_base).await
+                }));
+            }
+
+            let mut ok = 0usize;
+            let mut errors = Vec::new();
+            for (i, h) in handles.into_iter().enumerate() {
+                match h.await {
+                    Ok(Ok(())) => ok += 1,
+                    Ok(Err(e)) => errors.push(format!("client {}: {}", i, e)),
+                    Err(e) => errors.push(format!("client {} join: {}", i, e)),
+                }
+            }
+            assert!(
+                errors.is_empty(),
+                "clients failed (a V8 abort would instead kill the process): {:#?}",
+                errors
+            );
+            assert_eq!(ok as u64, CLIENTS, "every concurrent client must complete");
+        })
+        .await;
+}