fix: harden Lightpanda startup timeouts (#762)

cli/src/native/cdp/discovery.rs

@@ -0,0 +1,73 @@
+use std::time::Duration;
+
+use super::types::BrowserVersionInfo;
+
+pub async fn discover_cdp_url(port: u16) -> Result<String, String> {
+    discover_cdp_url_with_request_timeout(port, Duration::from_secs(2)).await
+}
+
+pub async fn discover_cdp_url_with_request_timeout(
+    port: u16,
+    request_timeout: Duration,
+) -> Result<String, String> {
+    let url = format!("http://127.0.0.1:{}/json/version", port);
+
+    let body = tokio::time::timeout(request_timeout, async { reqwest_get_string(&url).await })
+        .await
+        .map_err(|_| format!("Timeout connecting to CDP on port {}", port))?
+        .map_err(|e| format!("Failed to connect to CDP on port {}: {}", port, e))?;
+
+    let info: BrowserVersionInfo = serde_json::from_str(&body)
+        .map_err(|e| format!("Invalid /json/version response: {}", e))?;
+
+    info.web_socket_debugger_url
+        .ok_or_else(|| format!("No webSocketDebuggerUrl in /json/version on port {}", port))
+}
+
+async fn reqwest_get_string(url: &str) -> Result<String, String> {
+    let resp = reqwest::get(url).await.map_err(|e| e.to_string())?;
+    resp.text().await.map_err(|e| e.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    use tokio::net::TcpListener;
+
+    async fn spawn_json_server(body: &'static str) -> (u16, tokio::task::JoinHandle<()>) {
+        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+        let port = listener.local_addr().unwrap().port();
+        let handle = tokio::spawn(async move {
+            let (mut socket, _) = listener.accept().await.unwrap();
+            let mut buf = [0u8; 1024];
+            let _ = socket.read(&mut buf).await;
+            let response = format!(
+                "HTTP/1.1 200 OK\r\nContent-Length: {}\r\nConnection: close\r\nContent-Type: application/json\r\n\r\n{}",
+                body.len(),
+                body
+            );
+            socket.write_all(response.as_bytes()).await.unwrap();
+        });
+        (port, handle)
+    }
+
+    #[tokio::test]
+    async fn discovers_ws_url_from_json_version() {
+        let (port, server) =
+            spawn_json_server(r#"{"webSocketDebuggerUrl":"ws://127.0.0.1:1234/"}"#).await;
+
+        let ws_url = discover_cdp_url(port).await.unwrap();
+        assert_eq!(ws_url, "ws://127.0.0.1:1234/");
+        server.await.unwrap();
+    }
+
+    #[tokio::test]
+    async fn invalid_json_returns_parse_error() {
+        let (port, server) = spawn_json_server("not-json").await;
+
+        let err = discover_cdp_url(port).await.unwrap_err();
+        assert!(err.contains("Invalid /json/version response"));
+        server.await.unwrap();
+    }
+}