Harden Server-Timing fallback logging

Author: justin808

react_on_rails_pro/lib/react_on_rails_pro/concerns/stream.rb

@@ -174,8 +174,12 @@ def emit_rsc_stream_server_timing_header
       response.headers["Server-Timing"] = existing.present? ? "#{existing}, #{entry}" : entry
     rescue StandardError => e
       # Observability must never break a real response. Swallow and log.
-      Rails.logger.warn do
-        "[React on Rails Pro] Failed to emit RSC stream Server-Timing header: #{e.class}: #{e.message}"
+      begin
+        Rails.logger.warn(
+          "[React on Rails Pro] Failed to emit RSC stream Server-Timing header: #{e.class}: #{e.message}"
+        )
+      rescue StandardError
+        # Logging itself can fail if the logger is unavailable; keep the response alive.
       end
     end
 

react_on_rails_pro/spec/react_on_rails_pro/stream_spec.rb

@@ -225,6 +225,22 @@ def build_mocked_response
       expect(server_timing).to start_with("action_total;dur=5, ror_stream_shell;dur=")
     end
 
+    it "swallows Server-Timing header emission errors even when logging fails" do
+      _queues, controller, _stream = setup_stream_test(component_count: 0)
+      failing_headers = instance_double(Hash)
+      allow(failing_headers).to receive(:[]).and_raise(StandardError, "headers unavailable")
+      allow(controller.response).to receive(:headers).and_return(failing_headers)
+
+      failing_logger = instance_double(Logger)
+      allow(failing_logger).to receive(:warn).and_raise(StandardError, "logger unavailable")
+      allow(Rails).to receive(:logger).and_return(failing_logger)
+
+      controller.instance_variable_set(:@react_on_rails_rsc_stream_observability, true)
+      controller.instance_variable_set(:@react_on_rails_rsc_stream_initial_render_duration_ms, 12.3)
+
+      expect { controller.send(:emit_rsc_stream_server_timing_header) }.not_to raise_error
+    end
+
     it "escapes the final observability mark name inside the generated script" do
       _queues, controller, _stream = setup_stream_test(component_count: 0)