fix(security): block plaintext WebSocket connections to non-loopback addresses (#20803)

* fix(security): block plaintext WebSocket connections to non-loopback addresses

Addresses CWE-319 (Cleartext Transmission of Sensitive Information).

Previously, ws:// connections to remote hosts were allowed, exposing
both credentials and chat data to network interception. This change
blocks ALL plaintext ws:// connections to non-loopback addresses,
regardless of whether explicit credentials are configured (device
tokens may be loaded dynamically).

Security policy:
- wss:// allowed to any host
- ws:// allowed only to loopback (127.x.x.x, localhost, ::1)
- ws:// to LAN/tailnet/remote hosts now requires TLS

Changes:
- Add isSecureWebSocketUrl() validation in net.ts
- Block insecure connections in GatewayClient.start()
- Block insecure URLs in buildGatewayConnectionDetails()
- Handle malformed URLs gracefully without crashing
- Update tests to use wss:// for non-loopback URLs

Fixes #12519

* fix(test): update gateway-chat mock to preserve net.js exports

Use importOriginal to spread actual module exports and mock only
the functions needed for testing. This ensures isSecureWebSocketUrl
and other exports remain available to the code under test.

src/gateway/call.ts

@@ -16,7 +16,7 @@ import {
   type GatewayClientName,
 } from "../utils/message-channel.js";
 import { GatewayClient } from "./client.js";
-import { pickPrimaryLanIPv4 } from "./net.js";
+import { isSecureWebSocketUrl, pickPrimaryLanIPv4 } from "./net.js";
 import { PROTOCOL_VERSION } from "./protocol/index.js";
 
 export type CallGatewayOptions = {
@@ -134,6 +134,22 @@ export function buildGatewayConnectionDetails(
     ? "Warn: gateway.mode=remote but gateway.remote.url is missing; set gateway.remote.url or switch gateway.mode=local."
     : undefined;
   const bindDetail = !urlOverride && !remoteUrl ? `Bind: ${bindMode}` : undefined;
+
+  // Security check: block ALL insecure ws:// to non-loopback addresses (CWE-319, CVSS 9.8)
+  // This applies to the FINAL resolved URL, regardless of source (config, CLI override, etc).
+  // Both credentials and chat/conversation data must not be transmitted over plaintext to remote hosts.
+  if (!isSecureWebSocketUrl(url)) {
+    throw new Error(
+      [
+        `SECURITY ERROR: Gateway URL "${url}" uses plaintext ws:// to a non-loopback address.`,
+        "Both credentials and chat data would be exposed to network interception.",
+        `Source: ${urlSource}`,
+        `Config: ${configPath}`,
+        "Fix: Use wss:// for the gateway URL, or connect via SSH tunnel to localhost.",
+      ].join("\n"),
+    );
+  }
+
   const message = [
     `Gateway target: ${url}`,
     `Source: ${urlSource}`,