fix(security): harden SSH target handling (#4001)

Thanks @YLChen-007.

Co-authored-by: Edward-x <YLChen-007@users.noreply.github.com>

src/commands/gateway-status.test.ts

@@ -192,6 +192,45 @@ describe("gateway-status command", () => {
     expect(targets.some((t) => t.kind === "sshTunnel")).toBe(true);
   });
 
+  it("skips invalid ssh-auto discovery targets", async () => {
+    const runtimeLogs: string[] = [];
+    const runtime = {
+      log: (msg: string) => runtimeLogs.push(msg),
+      error: (_msg: string) => {},
+      exit: (code: number) => {
+        throw new Error(`__exit__:${code}`);
+      },
+    };
+
+    const originalUser = process.env.USER;
+    try {
+      process.env.USER = "steipete";
+      loadConfig.mockReturnValueOnce({
+        gateway: {
+          mode: "remote",
+          remote: {},
+        },
+      });
+      discoverGatewayBeacons.mockResolvedValueOnce([
+        { tailnetDns: "-V" },
+        { tailnetDns: "goodhost" },
+      ]);
+
+      startSshPortForward.mockClear();
+      const { gatewayStatusCommand } = await import("./gateway-status.js");
+      await gatewayStatusCommand(
+        { timeout: "1000", json: true, sshAuto: true },
+        runtime as unknown as import("../runtime.js").RuntimeEnv,
+      );
+
+      expect(startSshPortForward).toHaveBeenCalledTimes(1);
+      const call = startSshPortForward.mock.calls[0]?.[0] as { target: string };
+      expect(call.target).toBe("steipete@goodhost");
+    } finally {
+      process.env.USER = originalUser;
+    }
+  });
+
   it("infers SSH target from gateway.remote.url and ssh config", async () => {
     const runtimeLogs: string[] = [];
     const runtime = {