fix: captain json parsing (#13708)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Shivam Mishra <scm.mymail@gmail.com>

spec/enterprise/services/llm/base_ai_service_spec.rb

@@ -0,0 +1,35 @@
+require 'rails_helper'
+
+RSpec.describe Llm::BaseAiService do
+  subject(:service) { described_class.new }
+
+  before do
+    create(:installation_config, name: 'CAPTAIN_OPEN_AI_API_KEY', value: 'test-key')
+  end
+
+  describe '#sanitize_json_response' do
+    it 'strips ```json fences' do
+      input = "```json\n{\"key\": \"value\"}\n```"
+      expect(service.send(:sanitize_json_response, input)).to eq('{"key": "value"}')
+    end
+
+    it 'strips bare ``` fences' do
+      input = "```\n{\"key\": \"value\"}\n```"
+      expect(service.send(:sanitize_json_response, input)).to eq('{"key": "value"}')
+    end
+
+    it 'passes through plain JSON unchanged' do
+      input = '{"key": "value"}'
+      expect(service.send(:sanitize_json_response, input)).to eq('{"key": "value"}')
+    end
+
+    it 'returns nil for nil input' do
+      expect(service.send(:sanitize_json_response, nil)).to be_nil
+    end
+
+    it 'strips surrounding whitespace' do
+      input = "  \n{\"key\": \"value\"}\n  "
+      expect(service.send(:sanitize_json_response, input)).to eq('{"key": "value"}')
+    end
+  end
+end