fix(github-oauth): improve UX after OAuth flow

GitHubCallbackPage:
- Check sessionStorage before attempting exchange (prevents double-execution errors)
- Navigate with ?openGitHubImport=true param to auto-open modal
- Handle edge case where state already cleared (fast redirect)

DashboardHome:
- Read openGitHubImport param and auto-open GitHub import modal
- Clear param from URL after opening modal

GitHubRepoSelector:
- Add hasFetchedReposRef to prevent repeated fetch calls
- Only fetch repos once per modal open

Fixes: double callback errors, manual modal reopen after OAuth, repeated API calls

Author: DevanshuNEU

frontend/src/components/GitHubRepoSelector.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState, useEffect, useRef } from 'react';
 import { motion, AnimatePresence } from 'framer-motion';
 import { Github, Search, Lock, Star, Loader2, X, Check, AlertCircle, ExternalLink } from 'lucide-react';
 import { Button } from '@/components/ui/button';
@@ -24,6 +24,7 @@ export function GitHubRepoSelector({
   const [selected, setSelected] = useState<Set<number>>(new Set());
   const [searchQuery, setSearchQuery] = useState('');
   const [connecting, setConnecting] = useState(false);
+  const hasFetchedReposRef = useRef(false);
 
   const remainingSlots = maxSelectable - currentRepoCount;
 
@@ -33,11 +34,14 @@ export function GitHubRepoSelector({
       setSelected(new Set());
       setSearchQuery('');
       clearError();
+      hasFetchedReposRef.current = false;
     }
   }, [isOpen, checkStatus, clearError]);
 
   useEffect(() => {
-    if (isOpen && status?.connected) {
+    // Only fetch once per modal open, after status confirms connected
+    if (isOpen && status?.connected && !hasFetchedReposRef.current) {
+      hasFetchedReposRef.current = true;
       fetchRepos();
     }
   }, [isOpen, status?.connected, fetchRepos]);

frontend/src/components/dashboard/DashboardHome.tsx

@@ -1,4 +1,5 @@
 import { useState, useEffect } from 'react'
+import { useSearchParams } from 'react-router-dom'
 import { motion, AnimatePresence } from 'framer-motion'
 import { toast } from 'sonner'
 import { 
@@ -35,6 +36,7 @@ type RepoTab = 'overview' | 'search' | 'dependencies' | 'insights' | 'impact'
 
 export function DashboardHome() {
   const { session } = useAuth()
+  const [searchParams, setSearchParams] = useSearchParams()
   const [repos, setRepos] = useState<Repository[]>([])
   const [selectedRepo, setSelectedRepo] = useState<string | null>(null)
   const [activeTab, setActiveTab] = useState<RepoTab>('overview')
@@ -48,6 +50,16 @@ export function DashboardHome() {
   const [indexingRepoName, setIndexingRepoName] = useState<string>('')
   const [showIndexingModal, setShowIndexingModal] = useState(false)
 
+  // Auto-open GitHub import modal if redirected from OAuth callback
+  useEffect(() => {
+    if (searchParams.get('openGitHubImport') === 'true') {
+      setShowGitHubSelector(true)
+      // Clear the param from URL without triggering navigation
+      searchParams.delete('openGitHubImport')
+      setSearchParams(searchParams, { replace: true })
+    }
+  }, [searchParams, setSearchParams])
+
   const fetchRepos = async () => {
     if (!session?.access_token) return
     try {

frontend/src/pages/GitHubCallbackPage.tsx

@@ -16,13 +16,26 @@ export function GitHubCallbackPage() {
   useEffect(() => {
     // Prevent double-execution in React StrictMode
     if (callbackRanRef.current) return;
+    
+    const code = searchParams.get('code');
+    const state = searchParams.get('state');
+    
+    // Also check if we already processed this code (sessionStorage cleanup happens on success)
+    const storedState = sessionStorage.getItem('github_oauth_state');
+    if (!storedState) {
+      // State already cleared = already processed
+      setStatus('success');
+      timeoutRef.current = setTimeout(() => {
+        navigate('/dashboard?openGitHubImport=true', { replace: true });
+      }, 500);
+      return;
+    }
+    
     callbackRanRef.current = true;
 
     let mounted = true;
 
     const handleCallback = async () => {
-      const code = searchParams.get('code');
-      const state = searchParams.get('state');
       const error = searchParams.get('error');
       const errorDescription = searchParams.get('error_description');
 
@@ -53,7 +66,8 @@ export function GitHubCallbackPage() {
           setStatus('success');
           timeoutRef.current = setTimeout(() => {
             if (mounted) {
-              navigate('/dashboard', { replace: true });
+              // Navigate with param to auto-open import modal
+              navigate('/dashboard?openGitHubImport=true', { replace: true });
             }
           }, 1500);
         } else {