feat: cherry-pick PR #183 — multi-provider support, PWA, dynamic models, UI improvements

Cherry-picked from decolua/9router PR #183.
Note: open-sse changes included but need further review due to extensive modifications.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/sse/handlers/chat.js

@@ -28,7 +28,7 @@ export async function handleChat(request, clientRawRequest = null) {
     log.warn("CHAT", "Invalid JSON body");
     return errorResponse(HTTP_STATUS.BAD_REQUEST, "Invalid JSON body");
   }
-  
+
   // Build clientRawRequest for logging (if not provided)
   if (!clientRawRequest) {
     const url = new URL(request.url);
@@ -42,7 +42,7 @@ export async function handleChat(request, clientRawRequest = null) {
   // Log request endpoint and model
   const url = new URL(request.url);
   const modelStr = body.model;
-  
+
   // Count messages (support both messages[] and input[] formats)
   const msgCount = body.messages?.length || body.input?.length || 0;
   const toolCount = body.tools?.length || 0;
@@ -99,7 +99,19 @@ export async function handleChat(request, clientRawRequest = null) {
  */
 async function handleSingleModelChat(body, modelStr, clientRawRequest = null, request = null, apiKey = null) {
   const modelInfo = await getModelInfo(modelStr);
+
+  // If provider is null, this might be a combo name - check and handle
   if (!modelInfo.provider) {
+    const comboModels = await getComboModels(modelStr);
+    if (comboModels) {
+      log.info("CHAT", `Combo "${modelStr}" with ${comboModels.length} models`);
+      return handleComboChat({
+        body,
+        models: comboModels,
+        handleSingleModel: (b, m) => handleSingleModelChat(b, m, clientRawRequest, request, apiKey, forceSourceFormat),
+        log
+      });
+    }
     log.warn("CHAT", "Invalid model format", { model: modelStr });
     return errorResponse(HTTP_STATUS.BAD_REQUEST, "Invalid model format");
   }
@@ -178,12 +190,12 @@ async function handleSingleModelChat(body, modelStr, clientRawRequest = null, re
         await clearAccountError(credentials.connectionId, credentials);
       }
     });
-    
+
     if (result.success) return result.response;
 
     // Mark account unavailable (auto-calculates cooldown with exponential backoff)
     const { shouldFallback } = await markAccountUnavailable(credentials.connectionId, result.status, result.error, provider, model);
-    
+
     if (shouldFallback) {
       log.warn("AUTH", `Account ${accountId}... unavailable (${result.status}), trying fallback`);
       excludeConnectionId = credentials.connectionId;