fix: Restore soft-deleted users on re-authentication

convex/auth.ts

@@ -1,5 +1,6 @@
 import GitHub from '@auth/core/providers/github'
 import { convexAuth } from '@convex-dev/auth/server'
+import { Id } from './_generated/dataModel'
 
 export const { auth, signIn, signOut, store, isAuthenticated } = convexAuth({
   providers: [
@@ -16,4 +17,51 @@ export const { auth, signIn, signOut, store, isAuthenticated } = convexAuth({
       },
     }),
   ],
+  callbacks: {
+    /**
+     * Handle re-authentication of soft-deleted users.
+     *
+     * Performance note: This callback runs on every OAuth sign-in, but the
+     * audit log query ONLY executes when a soft-deleted user attempts to
+     * sign in (user.deletedAt is set). For normal active users, this is
+     * just a single `if` check on an already-loaded field - no extra queries.
+     */
+    async createOrUpdateUser(ctx, args) {
+      // New user - let Convex Auth handle creation with default behavior
+      if (!args.existingUserId) {
+        return null
+      }
+
+      const userId = args.existingUserId as Id<'users'>
+      const user = await ctx.db.get(userId)
+
+      // Active user - normal sign-in, no additional processing needed
+      if (!user?.deletedAt) {
+        return args.existingUserId
+      }
+
+      // Soft-deleted user attempting to sign in - check if banned or self-deleted
+      // Uses the by_target index for efficient lookup (not a full table scan)
+      const banRecord = await ctx.db
+        .query('auditLogs')
+        .withIndex('by_target', (q) =>
+          q.eq('targetType', 'user').eq('targetId', userId)
+        )
+        .filter((q) => q.eq(q.field('action'), 'user.ban'))
+        .first()
+
+      if (banRecord) {
+        // User was banned by a moderator - do NOT restore
+        throw new Error('This account has been suspended')
+      }
+
+      // User self-deleted their account - restore it
+      await ctx.db.patch(userId, {
+        deletedAt: undefined,
+        updatedAt: Date.now(),
+      })
+
+      return args.existingUserId
+    },
+  },
 })