Add Claude provider, OpenRouter fallback, and GFM markdown support

- Add Claude (Anthropic) as third LLM provider with streaming support
- Add OpenRouter as transparent fallback when official API keys are missing or fail
- Add remark-gfm to ReactMarkdown for table/strikethrough rendering
- Claude models: sonnet-4.5, opus-4, opus-4.5, opus-4.6
- Backend: new stream_claude(), stream_openrouter(), provider routing, API key CRUD
- Frontend: model selectors, API key inputs for Claude and OpenRouter
- Auto-migration for new DB columns (claude_api_key, openrouter_api_key)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

2 files changed, 86 insertions, 7 deletions

diff --git a/frontend/src/components/LeftSidebar.tsx b/frontend/src/components/LeftSidebar.tsx
index 6806ca3..5c464bb 100644
--- a/frontend/src/components/LeftSidebar.tsx
+++ b/frontend/src/components/LeftSidebar.tsx
@@ -62,8 +62,12 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ isOpen, onToggle }) => {
   const [openaiApiKey, setOpenaiApiKey] = useState('');
   const [geminiApiKey, setGeminiApiKey] = useState('');
   const [showGuide, setShowGuide] = useState(false);
+  const [claudeApiKey, setClaudeApiKey] = useState('');
+  const [openrouterApiKey, setOpenrouterApiKey] = useState('');
   const [showOpenaiKey, setShowOpenaiKey] = useState(false);
   const [showGeminiKey, setShowGeminiKey] = useState(false);
+  const [showClaudeKey, setShowClaudeKey] = useState(false);
+  const [showOpenrouterKey, setShowOpenrouterKey] = useState(false);
   const [savingKeys, setSavingKeys] = useState(false);
   const [keysMessage, setKeysMessage] = useState<{ type: 'success' | 'error'; text: string } | null>(null);
   const { getAuthHeader } = useAuthStore();
@@ -86,6 +90,8 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ isOpen, onToggle }) => {
         .then(data => {
           setOpenaiApiKey(data.openai_api_key || '');
           setGeminiApiKey(data.gemini_api_key || '');
+          setClaudeApiKey(data.claude_api_key || '');
+          setOpenrouterApiKey(data.openrouter_api_key || '');
         })
         .catch(() => {});
     }
@@ -101,6 +107,8 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ isOpen, onToggle }) => {
         body: JSON.stringify({
           openai_api_key: openaiApiKey.includes('*') ? undefined : openaiApiKey,
           gemini_api_key: geminiApiKey.includes('*') ? undefined : geminiApiKey,
+          claude_api_key: claudeApiKey.includes('*') ? undefined : claudeApiKey,
+          openrouter_api_key: openrouterApiKey.includes('*') ? undefined : openrouterApiKey,
         }),
       });
       if (res.ok) {
@@ -111,6 +119,8 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ isOpen, onToggle }) => {
         }).then(r => r.json());
         setOpenaiApiKey(data.openai_api_key || '');
         setGeminiApiKey(data.gemini_api_key || '');
+        setClaudeApiKey(data.claude_api_key || '');
+        setOpenrouterApiKey(data.openrouter_api_key || '');
       } else {
         setKeysMessage({ type: 'error', text: 'Failed to save API keys' });
       }
@@ -628,8 +638,8 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ isOpen, onToggle }) => {
                       onChange={e => setGeminiApiKey(e.target.value)}
                       placeholder="AI..."
                       className={`w-full px-3 py-2 pr-10 rounded-lg text-sm ${
-                        isDark 
-                          ? 'bg-gray-700 border-gray-600 text-white placeholder-gray-500' 
+                        isDark
+                          ? 'bg-gray-700 border-gray-600 text-white placeholder-gray-500'
                           : 'bg-white border-gray-300 text-gray-900 placeholder-gray-400'
                       } border focus:outline-none focus:ring-2 focus:ring-blue-500`}
                     />
@@ -643,6 +653,60 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ isOpen, onToggle }) => {
                   </div>
                 </div>
 
+                {/* Claude API Key */}
+                <div>
+                  <label className={`block text-xs mb-1 ${isDark ? 'text-gray-400' : 'text-gray-600'}`}>
+                    Claude API Key
+                  </label>
+                  <div className="relative">
+                    <input
+                      type={showClaudeKey ? 'text' : 'password'}
+                      value={claudeApiKey}
+                      onChange={e => setClaudeApiKey(e.target.value)}
+                      placeholder="sk-ant-..."
+                      className={`w-full px-3 py-2 pr-10 rounded-lg text-sm ${
+                        isDark
+                          ? 'bg-gray-700 border-gray-600 text-white placeholder-gray-500'
+                          : 'bg-white border-gray-300 text-gray-900 placeholder-gray-400'
+                      } border focus:outline-none focus:ring-2 focus:ring-blue-500`}
+                    />
+                    <button
+                      type="button"
+                      onClick={() => setShowClaudeKey(!showClaudeKey)}
+                      className={`absolute right-2 top-1/2 -translate-y-1/2 p-1 ${isDark ? 'text-gray-400' : 'text-gray-500'}`}
+                    >
+                      {showClaudeKey ? <EyeOff size={16} /> : <Eye size={16} />}
+                    </button>
+                  </div>
+                </div>
+
+                {/* OpenRouter API Key (Fallback) */}
+                <div>
+                  <label className={`block text-xs mb-1 ${isDark ? 'text-gray-400' : 'text-gray-600'}`}>
+                    OpenRouter API Key <span className={`text-[10px] ${isDark ? 'text-gray-500' : 'text-gray-400'}`}>(fallback)</span>
+                  </label>
+                  <div className="relative">
+                    <input
+                      type={showOpenrouterKey ? 'text' : 'password'}
+                      value={openrouterApiKey}
+                      onChange={e => setOpenrouterApiKey(e.target.value)}
+                      placeholder="sk-or-v1-..."
+                      className={`w-full px-3 py-2 pr-10 rounded-lg text-sm ${
+                        isDark
+                          ? 'bg-gray-700 border-gray-600 text-white placeholder-gray-500'
+                          : 'bg-white border-gray-300 text-gray-900 placeholder-gray-400'
+                      } border focus:outline-none focus:ring-2 focus:ring-blue-500`}
+                    />
+                    <button
+                      type="button"
+                      onClick={() => setShowOpenrouterKey(!showOpenrouterKey)}
+                      className={`absolute right-2 top-1/2 -translate-y-1/2 p-1 ${isDark ? 'text-gray-400' : 'text-gray-500'}`}
+                    >
+                      {showOpenrouterKey ? <EyeOff size={16} /> : <Eye size={16} />}
+                    </button>
+                  </div>
+                </div>
+
                 {/* Save Button */}
                 <button
                   onClick={handleSaveApiKeys}
diff --git a/frontend/src/components/Sidebar.tsx b/frontend/src/components/Sidebar.tsx
index 5141081..78d2475 100644
--- a/frontend/src/components/Sidebar.tsx
+++ b/frontend/src/components/Sidebar.tsx
@@ -5,6 +5,7 @@ import { useAuthStore } from '../store/authStore';
 import type { NodeData, Trace, Message, MergedTrace, MergeStrategy } from '../store/flowStore';
 import type { Edge } from 'reactflow';
 import ReactMarkdown from 'react-markdown';
+import remarkGfm from 'remark-gfm';
 import { Play, Settings, Info, ChevronLeft, ChevronRight, Maximize2, Edit3, X, Check, FileText, MessageCircle, Send, GripVertical, GitMerge, Trash2, AlertCircle, Loader2, Navigation, Upload, Search, Link } from 'lucide-react';
 
 interface SidebarProps {
@@ -312,7 +313,7 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
           scopes,
           merge_strategy: selectedNode.data.mergeStrategy || 'smart',
           config: {
-            provider: selectedNode.data.model.includes('gpt') || selectedNode.data.model === 'o3' ? 'openai' : 'google',
+            provider: selectedNode.data.model.includes('claude') ? 'claude' : (selectedNode.data.model.includes('gpt') || selectedNode.data.model === 'o3') ? 'openai' : 'google',
             model_name: selectedNode.data.model,
             temperature: selectedNode.data.temperature,
             system_prompt: selectedNode.data.systemPrompt,
@@ -1004,7 +1005,9 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
 
     try {
       // Determine provider
+      const isClaude = modelAtSend.includes('claude');
       const isOpenAI = modelAtSend.includes('gpt') || modelAtSend === 'o3';
+      const provider = isClaude ? 'claude' : isOpenAI ? 'openai' : 'google';
       const reasoningModels = ['gpt-5', 'gpt-5-chat-latest', 'gpt-5-mini', 'gpt-5-nano', 'gpt-5-pro', 'gpt-5.1', 'gpt-5.1-chat-latest', 'gpt-5.2', 'gpt-5.2-chat-latest', 'gpt-5.2-pro', 'o3'];
       const isReasoning = reasoningModels.includes(modelAtSend);
 
@@ -1024,7 +1027,7 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
           scopes,
           merge_strategy: 'smart',
           config: {
-            provider: isOpenAI ? 'openai' : 'google',
+            provider,
             model_name: modelAtSend,
             temperature: isReasoning ? 1 : tempAtSend,
             enable_google_search: webSearchAtSend,
@@ -1424,6 +1427,12 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
                 }}
                 className="w-full border border-gray-300 rounded-md p-2 text-sm"
               >
+                <optgroup label="Claude">
+                  <option value="claude-sonnet-4-5">claude-sonnet-4.5</option>
+                  <option value="claude-opus-4">claude-opus-4</option>
+                  <option value="claude-opus-4-5">claude-opus-4.5</option>
+                  <option value="claude-opus-4-6">claude-opus-4.6</option>
+                </optgroup>
                 <optgroup label="Gemini">
                   <option value="gemini-2.5-flash">gemini-2.5-flash</option>
                   <option value="gemini-2.5-flash-lite">gemini-2.5-flash-lite</option>
@@ -1841,7 +1850,7 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
                     ? 'bg-gray-900 border-gray-700 prose-invert text-gray-200' 
                     : 'bg-gray-50 border-gray-200 text-gray-900'
                 }`}>
-                  <ReactMarkdown>{selectedNode.data.response || (streamingNodeId === selectedNode.id ? streamBuffer : '')}</ReactMarkdown>
+                  <ReactMarkdown remarkPlugins={[remarkGfm]}>{selectedNode.data.response || (streamingNodeId === selectedNode.id ? streamBuffer : '')}</ReactMarkdown>
                 </div>
               )}
             </div>
@@ -2135,7 +2144,7 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
                 />
               ) : (
                 <div className="prose prose-sm max-w-none">
-                  <ReactMarkdown>{selectedNode.data.response}</ReactMarkdown>
+                  <ReactMarkdown remarkPlugins={[remarkGfm]}>{selectedNode.data.response}</ReactMarkdown>
                 </div>
               )}
             </div>
@@ -2419,6 +2428,12 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
                     isDark ? 'bg-gray-700 border-gray-600 text-gray-200' : 'border-gray-300 text-gray-900'
                   }`}
                 >
+                  <optgroup label="Claude">
+                    <option value="claude-sonnet-4-5">claude-sonnet-4.5</option>
+                    <option value="claude-opus-4">claude-opus-4</option>
+                    <option value="claude-opus-4-5">claude-opus-4.5</option>
+                    <option value="claude-opus-4-6">claude-opus-4.6</option>
+                  </optgroup>
                   <optgroup label="Gemini">
                     <option value="gemini-2.5-flash">gemini-2.5-flash</option>
                     <option value="gemini-2.5-flash-lite">gemini-2.5-flash-lite</option>
@@ -2520,7 +2535,7 @@ const Sidebar: React.FC<SidebarProps> = ({ isOpen, onToggle, onInteract }) => {
                             <p className="whitespace-pre-wrap">{msg.content}</p>
                           ) : (
                             <div className={`prose prose-sm max-w-none ${isDark ? 'prose-invert' : ''}`}>
-                              <ReactMarkdown>{msg.content}</ReactMarkdown>
+                              <ReactMarkdown remarkPlugins={[remarkGfm]}>{msg.content}</ReactMarkdown>
                             </div>
                           )}
                         </div>