gateway: a vendor refusing the client outright (WorkBuddy's 400 "Illegal API invocation from an unapproved channel") hands a group's request to its next member (PR #232 Y-C-Fan: a routing group stopped at a WorkBuddy member refusing Claude Code's chats) — retryable let a 400 fall over only on quota or unserved-model words, so this refusal, which is of the provider and not the request, went back to the agent. A new refusedWords (unapproved channel, illegal api invocation) joins them. The request body is not changed: a chat opening with Claude Code's own system prompt is still sent as it came. Tested with a new case in TestGroupFailsOverAnUnservedModel's retryable table (false before) and the gateway package.

internal/gateway/fallback.go

@@ -411,6 +411,12 @@ var quotaWords = regexp.MustCompile(`(?i)quota|insufficient|balance|credit|billi
 // key, or this way — words another provider, or key, may not answer with.
 var unservedWords = regexp.MustCompile(`(?i)model.{0,80}(not (supported|accessible|available|found|enabled|allowed)|unsupported|does ?n[o']t exist|unknown|invalid)|(no such|unknown|invalid|unsupported) model|model_not_found|模型.{0,12}(不存在|不支持|无权|未开通)`)
 
+// refusedWords are how a vendor says it won't take requests from this
+// client at all — WorkBuddy's "Illegal API invocation from an unapproved
+// channel" to a chat opening with another agent's own system prompt — a
+// refusal of the provider, not of the request, another member may serve.
+var refusedWords = regexp.MustCompile(`(?i)unapproved channel|illegal api invocation`)
+
 // retryable says whether another provider may do better with a request
 // that failed this way: the vendor was busy, out of quota or failing, or
 // this key or provider can't serve it — not the request itself at fault.
@@ -419,7 +425,7 @@ func retryable(status int, body []byte) bool {
 	case status == 401, status == 402, status == 403, status == 404, status == 408, status == 429, status >= 500:
 		return true
 	case status == 400, status == 422:
-		return quotaWords.Match(body) || unservedWords.Match(body)
+		return quotaWords.Match(body) || unservedWords.Match(body) || refusedWords.Match(body)
 	}
 	return false
 }

internal/gateway/retry_test.go

@@ -90,6 +90,7 @@ func TestGroupFailsOverAnUnservedModel(t *testing.T) {
 		{400, `{"error":{"message":"The model gpt-x does not exist"}}`, true},
 		{400, `{"error":{"message":"messages: field required"}}`, false},
 		{400, `{"error":{"message":"This model's maximum context length is 128000 tokens"}}`, false},
+		{400, `{"error":{"message":"Illegal API invocation from an unapproved channel"}}`, true},
 	} {
 		if got := retryable(x.status, []byte(x.body)); got != x.want {
 			t.Errorf("retryable(%d, %s) = %v", x.status, x.body, got)