diff --git a/src/app/api/auth/register/route.ts b/src/app/api/auth/register/route.ts
index 9fbbfd1..ea8c7bd 100644
--- a/src/app/api/auth/register/route.ts
+++ b/src/app/api/auth/register/route.ts
@@ -1,5 +1,6 @@
 import { NextResponse } from "next/server";
 import { prisma } from "@/lib/prisma";
+import { Prisma } from "@prisma/client";
 import bcrypt from "bcryptjs";
 import { apiHandler, ApiError } from "@/lib/api";
 import { validateUsername, validatePassword } from "@/lib/validation";
@@ -12,22 +13,26 @@ export const POST = apiHandler(async (req) => {
   const trimmedUsername = validateUsername(username);
   validatePassword(password);
 
-  const existing = await prisma.user.findUnique({ where: { username: trimmedUsername } });
-  if (existing) throw new ApiError("用户名已被注册", 409);
-
   const passwordHash = await bcrypt.hash(password, 10);
 
-  const user = await prisma.user.create({
-    data: {
-      username: trimmedUsername,
-      passwordHash,
-      avatar: avatar || "🐱",
-    },
-  });
+  try {
+    const user = await prisma.user.create({
+      data: {
+        username: trimmedUsername,
+        passwordHash,
+        avatar: avatar || "🐱",
+      },
+    });
 
-  return NextResponse.json({
-    id: user.id,
-    username: user.username,
-    avatar: user.avatar,
-  });
+    return NextResponse.json({
+      id: user.id,
+      username: user.username,
+      avatar: user.avatar,
+    });
+  } catch (e) {
+    if (e instanceof Prisma.PrismaClientKnownRequestError && e.code === "P2002") {
+      throw new ApiError("用户名已被注册", 409);
+    }
+    throw e;
+  }
 });
diff --git a/src/app/api/user/route.ts b/src/app/api/user/route.ts
index 6f07c9e..d9a0a2d 100644
--- a/src/app/api/user/route.ts
+++ b/src/app/api/user/route.ts
@@ -1,5 +1,6 @@
 import { NextResponse } from "next/server";
 import { prisma } from "@/lib/prisma";
+import { Prisma } from "@prisma/client";
 import bcrypt from "bcryptjs";
 import { apiHandler, ApiError, requireUserId, requireUser } from "@/lib/api";
 import { validateUsername, validatePassword, validateEmail } from "@/lib/validation";
@@ -13,12 +14,15 @@ export const GET = apiHandler(async (req) => {
 
   const decisionCount = await prisma.decision.count({ where: { userId } });
 
+  let preferences = {};
+  try { preferences = JSON.parse(user.preferences); } catch { /* fallback */ }
+
   return NextResponse.json({
     id: user.id,
     username: user.username,
     avatar: user.avatar,
     email: user.email,
-    preferences: JSON.parse(user.preferences),
+    preferences,
     createdAt: user.createdAt.toISOString(),
     decisionCount,
   });
@@ -63,16 +67,23 @@ export const PUT = apiHandler(async (req) => {
     updateData.preferences = JSON.stringify(body.preferences);
   }
 
-  const user = await prisma.user.update({
-    where: { id: userId },
-    data: updateData,
-  });
+  try {
+    const user = await prisma.user.update({
+      where: { id: userId },
+      data: updateData,
+    });
 
-  return NextResponse.json({
-    id: user.id,
-    username: user.username,
-    avatar: user.avatar,
-    email: user.email,
-    preferences: JSON.parse(user.preferences),
-  });
+    return NextResponse.json({
+      id: user.id,
+      username: user.username,
+      avatar: user.avatar,
+      email: user.email,
+      preferences: JSON.parse(user.preferences),
+    });
+  } catch (e) {
+    if (e instanceof Prisma.PrismaClientKnownRequestError && e.code === "P2002") {
+      throw new ApiError("用户名已被占用", 409);
+    }
+    throw e;
+  }
 });
diff --git a/src/lib/api.ts b/src/lib/api.ts
index 33d1e46..f3879dc 100644
--- a/src/lib/api.ts
+++ b/src/lib/api.ts
@@ -1,4 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
+import { Prisma } from "@prisma/client";
 import { prisma } from "@/lib/prisma";
 
 export class ApiError extends Error {
@@ -7,6 +8,7 @@ export class ApiError extends Error {
     public status: number = 400,
   ) {
     super(message);
+    this.name = "ApiError";
   }
 }
 
@@ -45,6 +47,15 @@ export function apiHandler(handler: RouteHandler): RouteHandler {
       if (e instanceof ApiError) {
         return NextResponse.json({ error: e.message }, { status: e.status });
       }
+      if (
+        e instanceof Prisma.PrismaClientKnownRequestError &&
+        e.code === "P2002"
+      ) {
+        return NextResponse.json(
+          { error: "该记录已存在或值已被占用" },
+          { status: 409 },
+        );
+      }
       console.error(`[API ${req.method} ${req.nextUrl.pathname}]`, e);
       return NextResponse.json({ error: "操作失败" }, { status: 500 });
     }
diff --git a/src/lib/validation.ts b/src/lib/validation.ts
index c9f5b5b..f400757 100644
--- a/src/lib/validation.ts
+++ b/src/lib/validation.ts
@@ -12,6 +12,9 @@ export function validatePassword(password: string, label = "密码"): void {
   if (password.length < 6) {
     throw new ApiError(`${label}至少 6 个字符`);
   }
+  if (password.length > 128) {
+    throw new ApiError(`${label}不能超过 128 个字符`);
+  }
 }
 
 export function validateEmail(email: string): void {