fix(gemini): accept signature-only reasoning exhaustion

apps/aether-gateway/src/execution_runtime/sync/execution.rs

@@ -3774,6 +3774,33 @@ mod tests {
         assert!(message.is_none());
     }
 
+    #[test]
+    fn invalid_gemini_provider_stream_success_accepts_signature_only_reasoning_exhaustion() {
+        let plan = test_gemini_chat_plan();
+        let report_context = json!({
+            "has_envelope": true,
+            "envelope_name": "antigravity:v1internal",
+            "provider_api_format": "gemini:generate_content",
+        });
+        let body = concat!(
+            "data: {\"response\":{\"responseId\":\"resp_signature_only_123\",\"modelVersion\":\"gemini-3.7-flash-tiered\",",
+            "\"candidates\":[{\"index\":0,\"content\":{\"role\":\"model\",\"parts\":[{\"text\":\"\",\"thoughtSignature\":\"opaque-thought-signature\"}]},\"finishReason\":\"MAX_TOKENS\"}],",
+            "\"usageMetadata\":{\"promptTokenCount\":22,\"thoughtsTokenCount\":29,\"totalTokenCount\":51}},",
+            "\"traceId\":\"trace-signature-only\"}\n\n",
+        );
+
+        let message = invalid_gemini_provider_stream_success_message(
+            &plan,
+            Some(&report_context),
+            StatusCode::OK.as_u16(),
+            None,
+            body.as_bytes(),
+            true,
+        );
+
+        assert!(message.is_none());
+    }
+
     #[test]
     fn invalid_gemini_provider_success_error_is_retryable_candidate_failure() {
         let error = invalid_gemini_provider_success_execution_error(