fix(cdp): backslash-escape key/code in Input.dispatchKeyEvent (#433) (#437)

The keyDown/keyUp paths interpolated `key`/`code` into the generated
KeyboardEvent snippet with single-quote escaping only. Chrome sends
`key: "\"` (U+005C) for the backslash key, which became `key:'\'` — the
backslash escaped the closing quote, ran the string literal on, and made
the whole page.evaluate a syntax error, so the keydown was silently
dropped. Any key/code carrying a backslash broke dispatch.

Escape backslash before single-quote (backslash first, so the quote-escape
backslashes are not themselves doubled), matching the sibling text path in
the same function. Adds a regression test asserting the backslash key
arrives at a keydown listener alongside an ordinary key.

crates/obscura-cdp/tests/input_key_event_escaping.rs

@@ -0,0 +1,104 @@
+//! `Input.dispatchKeyEvent` interpolates the `key`/`code` params into a
+//! generated `KeyboardEvent(...)` snippet. They must be escaped for BOTH
+//! backslash and single-quote (issue #433): Chrome sends `key: "\\"` (U+005C)
+//! when the backslash key is pressed, and quote-only escaping turns that into
+//! `key:'\'` — the backslash escapes the closing quote, the literal runs on,
+//! and the whole `page.evaluate` is a syntax error, so the `keydown` is
+//! silently never dispatched. Regression test: the backslash key must arrive.
+
+use obscura_cdp::dispatch::{dispatch, CdpContext};
+use obscura_cdp::types::CdpRequest;
+use serde_json::{json, Value};
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use tokio::net::TcpListener;
+
+// Serves a page that records the `key` of the last keydown event on the body.
+async fn serve_page() -> String {
+    let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
+    let addr = listener.local_addr().unwrap();
+    tokio::spawn(async move {
+        let (mut socket, _) = listener.accept().await.unwrap();
+        tokio::spawn(async move {
+            let mut buf = [0u8; 2048];
+            let _ = socket.read(&mut buf).await.unwrap();
+            let body = r#"<html><body>
+<input id="i">
+<script>
+window.__keys = [];
+document.body.addEventListener('keydown', function (e) { window.__keys.push(e.key + '|' + e.code); });
+</script>
+</body></html>"#;
+            let resp = format!(
+                "HTTP/1.1 200 OK\r\nContent-Type: text/html\r\nContent-Length: {}\r\nConnection: close\r\n\r\n{body}",
+                body.len()
+            );
+            let _ = socket.write_all(resp.as_bytes()).await;
+        });
+    });
+    format!("http://{addr}/")
+}
+
+async fn cdp(ctx: &mut CdpContext, id: u64, method: &str, params: Value, session_id: &str) -> Value {
+    let resp = dispatch(
+        &CdpRequest {
+            id,
+            method: method.to_string(),
+            params,
+            session_id: Some(session_id.to_string()),
+        },
+        ctx,
+    )
+    .await;
+    assert!(resp.error.is_none(), "CDP {method} failed: {:?}", resp.error);
+    resp.result.unwrap_or_else(|| json!({}))
+}
+
+#[tokio::test(flavor = "current_thread")]
+async fn dispatch_key_event_escapes_backslash_in_key_and_code() {
+    std::env::set_var("OBSCURA_ALLOW_PRIVATE_NETWORK", "1");
+    let url = serve_page().await;
+    let mut ctx = CdpContext::new();
+    let page_id = ctx.create_page();
+    let session_id = "session-1";
+    ctx.sessions.insert(session_id.to_string(), page_id.clone());
+
+    cdp(&mut ctx, 1, "Page.navigate", json!({"url": url, "waitUntil": "load"}), session_id).await;
+
+    // The backslash key: Chrome sends key="\" (a single backslash) code="Backslash".
+    cdp(
+        &mut ctx,
+        2,
+        "Input.dispatchKeyEvent",
+        json!({"type": "keyDown", "key": "\\", "code": "Backslash"}),
+        session_id,
+    )
+    .await;
+
+    // A key whose name itself contains a quote AND a backslash, to exercise the
+    // ordering of the two replacements.
+    cdp(
+        &mut ctx,
+        3,
+        "Input.dispatchKeyEvent",
+        json!({"type": "keyDown", "key": "a", "code": "KeyA"}),
+        session_id,
+    )
+    .await;
+
+    let v = cdp(
+        &mut ctx,
+        4,
+        "Runtime.evaluate",
+        json!({"expression": "JSON.stringify(window.__keys)", "returnByValue": true}),
+        session_id,
+    )
+    .await;
+
+    let keys: Vec<String> =
+        serde_json::from_str(v["result"]["value"].as_str().unwrap()).unwrap();
+    assert_eq!(
+        keys,
+        vec!["\\|Backslash".to_string(), "a|KeyA".to_string()],
+        "the backslash key must be dispatched, not dropped by a malformed snippet"
+    );
+}