From 327d65806994ff0c44c95fd32e276782cfa05dec Mon Sep 17 00:00:00 2001
From: Lawrence Chen <54008264+lawrencecchen@users.noreply.github.com>
Date: Fri, 20 Feb 2026 14:53:00 -0800
Subject: [PATCH] Fix CLI v2 commands showing JSON parse error instead of
 actual error (#189)

When the server returns a plain-text error (e.g., "ERROR: Access denied
...") before the JSON protocol starts, sendV2() would pass it through
JSONSerialization which throws a confusing NSCocoaErrorDomain 3840 error.

Now sendV2() checks for "ERROR:" prefix and surfaces the real message.
Also includes the raw response in the fallback error for easier debugging.

Fixes https://github.com/manaflow-ai/cmux/issues/188
---
 CLI/cmux.swift | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/CLI/cmux.swift b/CLI/cmux.swift
index 9220afd8..bdb617b4 100644
--- a/CLI/cmux.swift
+++ b/CLI/cmux.swift
@@ -365,11 +365,19 @@ final class SocketClient {
         }
 
         let raw = try send(command: requestLine)
+
+        // The server may return plain-text errors (e.g., "ERROR: Access denied ...")
+        // before the JSON protocol starts. Surface these directly instead of letting
+        // JSONSerialization throw a confusing parse error.
+        if raw.hasPrefix("ERROR:") {
+            throw CLIError(message: raw)
+        }
+
         guard let responseData = raw.data(using: .utf8) else {
             throw CLIError(message: "Invalid UTF-8 v2 response")
         }
         guard let response = try JSONSerialization.jsonObject(with: responseData, options: []) as? [String: Any] else {
-            throw CLIError(message: "Invalid v2 response")
+            throw CLIError(message: "Invalid v2 response: \(raw)")
         }
 
         if let ok = response["ok"] as? Bool, ok {