add content type guard catch

src/convox/_http.py

@@ -237,6 +237,18 @@ def request(
             request_id = response.headers.get("request-id")
             raise exception_for_response(response.status_code, message, request_id)
 
+        # Guard against non-JSON success responses.  The Convox console
+        # returns its HTML UI when no Rack header is present; without
+        # this check callers would get an opaque JSONDecodeError.
+        ct = response.headers.get("content-type", "")
+        if "text/html" in ct:
+            raise exception_for_response(
+                502,
+                "Expected JSON response but received HTML. "
+                "If you are connecting through a Convox console, "
+                "make sure the 'rack' parameter is set.",
+            )
+
         return response
 
     def get(self, path: str, **kwargs: Any) -> httpx.Response:

src/convox/client.py

@@ -110,7 +110,7 @@ def from_env(
         import os
 
         host, api_key = credentials_from_env()
-        rack = os.environ.get("CONVOX_RACK")
+        rack = os.environ.get("CONVOX_RACK") or None
         return cls(host, api_key, rack=rack, retry=retry, timeout=timeout)
 
     @classmethod