fix(webcrt): replay login banner/prompt on attach

Drain and nudge the device prompt after Netmiko login, replay bootstrap stdout when the WebSocket attaches, and surface connect errors in the terminal pane.

Co-authored-by: Cursor <cursoragent@cursor.com>

netx_api/webcrt_router.py

@@ -93,9 +93,27 @@ async def websocket_session(websocket: WebSocket, session_id: str) -> None:
             "protocol": sess.protocol,
             "cols": sess.cols,
             "rows": sess.rows,
+            "device_type": sess.device_type,
+            "vendor": sess.vendor,
         }
     )
 
+    # Replay post-login banner/prompt so the UI is not blank until the user presses Enter.
+    bootstrap = bytes(sess.bootstrap_output or b"")
+    if bootstrap:
+        try:
+            await websocket.send_json(
+                {"type": "stdout", "data": bootstrap.decode("utf-8", errors="replace")}
+            )
+        except Exception:
+            _log.debug("webcrt bootstrap send failed session=%s", session_id, exc_info=True)
+    else:
+        # Last resort: ask the device to redraw the prompt into the live reader.
+        try:
+            await asyncio.get_running_loop().run_in_executor(None, sess.write_stdin, "\r")
+        except Exception:
+            pass
+
     stop = asyncio.Event()
 
     async def pump_stdout() -> None:

netx_api/webcrt_service.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 import json
 import logging
 import queue
+import re
 import threading
 import time
 import uuid
@@ -76,6 +77,35 @@ def map_network_cli_keys(data: str) -> str:
             i += 1
     return "".join(out)
 
+def _drain_channel(conn: ConnectHandler, *, rounds: int = 10, wait: float = 0.12) -> str:
+    """Read whatever is already sitting on the channel after login."""
+    chunks: list[str] = []
+    empty_streak = 0
+    for _ in range(max(1, rounds)):
+        time.sleep(wait)
+        try:
+            part = conn.read_channel()
+        except Exception:
+            break
+        if part:
+            chunks.append(str(part))
+            empty_streak = 0
+        else:
+            empty_streak += 1
+            if empty_streak >= 2 and chunks:
+                break
+    return "".join(chunks)
+
+
+def _looks_like_cli_prompt(text: str) -> bool:
+    s = str(text or "").rstrip()
+    if not s:
+        return False
+    # Common network CLI prompts: <r1>  [HUAWEI]  Router#  Router>
+    return bool(re.search(r"(?:[>\]]|#)\s*$", s)) or bool(re.search(r"<[^>\r\n]+>\s*$", s))
+
+
+
 def _utc_now() -> datetime:
     return datetime.now(timezone.utc)
 
@@ -120,6 +150,7 @@ class WebcrtSession:
     detach_deadline: float | None = None
     closed: bool = False
     close_reason: str = ""
+    bootstrap_output: bytes = b""
     out_queue: queue.Queue[bytes | None] = field(default_factory=queue.Queue)
     _reader: threading.Thread | None = field(default=None, repr=False)
     _write_lock: threading.Lock = field(default_factory=threading.Lock, repr=False)
@@ -358,9 +389,19 @@ def create_session(
             pass
 
     try:
-        leftover = conn.read_channel()
+        leftover = _drain_channel(conn, rounds=8, wait=0.1)
     except Exception:
         leftover = ""
+    # Netmiko often consumes the login banner; nudge Enter once to surface the prompt.
+    if not _looks_like_cli_prompt(leftover):
+        try:
+            conn.write_channel("\r")
+        except Exception:
+            pass
+        try:
+            leftover = (leftover or "") + _drain_channel(conn, rounds=8, wait=0.12)
+        except Exception:
+            pass
 
     sess = WebcrtSession(
         session_id=session_id,
@@ -374,9 +415,9 @@ def create_session(
         vendor=vendor,
         cli_keymap=cli_keymap,
         conn=conn,
+        bootstrap_output=str(leftover or "").encode("utf-8", errors="replace"),
     )
-    if leftover:
-        sess.out_queue.put(str(leftover).encode("utf-8", errors="replace"))
+    # Keep bootstrap for WS attach replay; do not rely solely on out_queue (StrictMode remount).
     sess.start_reader()
 
     with _sessions_lock:

tests/test_webcrt.py

@@ -145,8 +145,11 @@ class WebcrtServiceTests(unittest.TestCase):
         self.assertEqual(out["ne_id"], "ne-hop")
         sess = svc.get_session(out["session_id"])
         assert sess is not None
+        # create_session may nudge Enter when no prompt was drained.
+        before = list(fake.written)
         sess.write_stdin("\n")
-        self.assertEqual(fake.written, ["\n"])
+        self.assertEqual(fake.written[len(before) :], ["\n"])
+        self.assertTrue(isinstance(sess.bootstrap_output, (bytes, bytearray)))
         svc.close_session(out["session_id"], reason="test")
 
     @patch.object(svc, "_audit")

web/src/components/WebTerminal.tsx

@@ -75,7 +75,6 @@ export function WebTerminal({ wsUrl, title, onStatus, onReady }: Props) {
 
     ws.onopen = () => {
       onStatusRef.current?.("open");
-      term.writeln("\x1b[32mConnected.\x1b[0m");
       sendResize();
       onReadyRef.current?.();
     };
@@ -87,6 +86,9 @@ export function WebTerminal({ wsUrl, title, onStatus, onReady }: Props) {
           data?: string;
           state?: string;
           message?: string;
+          ne_name?: string;
+          ne_ip?: string;
+          protocol?: string;
         };
         if (msg.type === "stdout" && typeof msg.data === "string") {
           term.write(msg.data);
@@ -95,7 +97,8 @@ export function WebTerminal({ wsUrl, title, onStatus, onReady }: Props) {
         if (msg.type === "status") {
           onStatusRef.current?.(String(msg.state || ""), msg.message);
           if (msg.state === "connected") {
-            // Server ack; keep terminal clean.
+            const where = [msg.ne_name || title, msg.ne_ip, msg.protocol].filter(Boolean).join(" · ");
+            term.writeln(`\x1b[90m--- session ready${where ? `: ${where}` : ""} ---\x1b[0m`);
             return;
           }
           if (msg.state === "closed" || msg.state === "error") {

web/src/index.css

@@ -1741,6 +1741,16 @@ pre {
   color: #fecaca;
 }
 
+.webcrt-error-detail {
+  margin: 8px 0 0;
+  max-width: 80%;
+  white-space: pre-wrap;
+  word-break: break-word;
+  font-size: 12px;
+  color: #fee2e2;
+  text-align: left;
+}
+
 .webcrt-statusline {
   padding: 3px 8px;
   background: #ececec;

web/src/pages/WebcrtPage.tsx

@@ -22,6 +22,7 @@ type TermTab = {
   wsUrl: string;
   target: CliTargetItem;
   status: "connecting" | "connected" | "error" | "closed";
+  errorMessage?: string;
 };
 
 function targetKey(t: Pick<CliTargetItem, "source" | "id">): string {
@@ -120,8 +121,9 @@ export function WebcrtPage() {
         updateTab(key, { sessionId: sess.session_id, wsUrl, status: "connecting" });
         showOk(t("webcrt.opened", { name: target.name || target.ip_address }));
       } catch (err) {
-        updateTab(key, { status: "error" });
-        showError(webcrtErrorMessage(err, t));
+        const message = webcrtErrorMessage(err, t);
+        updateTab(key, { status: "error", errorMessage: message });
+        showError(message);
       } finally {
         connectingKeysRef.current.delete(key);
       }
@@ -344,7 +346,8 @@ export function WebcrtPage() {
                   ) : null}
                   {tab.status === "error" && !tab.wsUrl ? (
                     <div className="webcrt-main__placeholder webcrt-main__placeholder--error">
-                      {t("webcrt.status.error")}
+                      <div>{t("webcrt.status.error")}</div>
+                      {tab.errorMessage ? <pre className="webcrt-error-detail">{tab.errorMessage}</pre> : null}
                     </div>
                   ) : null}
                   {tab.wsUrl ? (