diff --git a/apps/api/src/flowchart/run.ts b/apps/api/src/flowchart/run.ts
index 75b6182..06dcfd7 100644
--- a/apps/api/src/flowchart/run.ts
+++ b/apps/api/src/flowchart/run.ts
@@ -15,22 +15,38 @@ function evaluationPrompt(problem: typeof schema.problem.$inferSelect) {
 题目：${problem.title}\n${problem.description.slice(0, 2000)}`
 }
 
+/**
+ * 等级一律由分数推出来，不采信模型自报的 grade。
+ * 提示词里写死了这四档，但模型偶尔会给出 88 分配 S 级这种自相矛盾的结果，
+ * 甚至直接吐「优秀」；脏值会一路串到等级分布图和「A/S 才展示流程图」的判断里。
+ */
+function gradeForScore(score: number) {
+  if (score >= 90) return "S"
+  if (score >= 80) return "A"
+  if (score >= 70) return "B"
+  return "C"
+}
+
 function parseEvaluation(value: string) {
   const block = value.match(/```(?:json)?\s*([\s\S]*?)```/)?.[1]
   const json = block ?? value.match(/\{[\s\S]*\}/)?.[0]
   if (!json) throw new Error("AI response did not contain JSON")
   const data = JSON.parse(json) as Record<string, unknown>
-  if (typeof data.score !== "number" || typeof data.grade !== "string") throw new Error("AI response is missing score or grade")
+  if (typeof data.score !== "number" || Number.isNaN(data.score)) throw new Error("AI response is missing score")
+  const score = Math.max(0, Math.min(100, data.score))
   return {
-    score: Math.max(0, Math.min(100, data.score)),
-    grade: data.grade,
+    score,
+    grade: gradeForScore(score),
     feedback: typeof data.feedback === "string" ? data.feedback : "",
     suggestions: typeof data.suggestions === "string" ? data.suggestions : "",
     criteria: data.criteria_details && typeof data.criteria_details === "object" ? data.criteria_details : {},
   }
 }
 
-export async function evaluateFlowchart(job: FlowchartJobData) {
+export async function evaluateFlowchart(
+  job: FlowchartJobData,
+  { isFinalAttempt = true }: { isFinalAttempt?: boolean } = {},
+) {
   const [row] = await db.select({ flowchart: schema.flowchartSubmission, problem: schema.problem }).from(schema.flowchartSubmission)
     .innerJoin(schema.problem, eq(schema.flowchartSubmission.problemId, schema.problem.id))
     .where(eq(schema.flowchartSubmission.id, job.submissionId)).limit(1)
@@ -69,6 +85,11 @@ export async function evaluateFlowchart(job: FlowchartJobData) {
     // AI provider 的地址、内部报错就这么进了浏览器。真实原因留在服务端日志里，
     // 学生只需要知道「失败了，再试一次」；error 字段留空，前端有兜底文案。
     console.error(`Failed to evaluate flowchart ${row.flowchart.id}`, error)
+    // 只有最后一次尝试才落 FAILED。中间几次必须把状态留在 PROCESSING(1)：
+    // 上面那道 `![0, 1].includes(status)` 的守卫会把状态为 3 的任务直接放行返回，
+    // 一旦提前写成 3，队列配的 attempts: 3 就成了摆设 —— 后两次尝试进来什么都不做
+    // 就算成功，AI 侧的偶发失败（限流、超时、网络抖动）永远等不到重试。
+    if (!isFinalAttempt) throw error
     await db.update(schema.flowchartSubmission).set({ status: 3 }).where(eq(schema.flowchartSubmission.id, row.flowchart.id))
     await publishFlowchartUpdate(row.flowchart.userId, flowchartUpdateSchema.parse({
       type: "flowchart_evaluation_failed",
diff --git a/apps/api/src/services/ai.ts b/apps/api/src/services/ai.ts
index 9059881..004bc52 100644
--- a/apps/api/src/services/ai.ts
+++ b/apps/api/src/services/ai.ts
@@ -15,10 +15,18 @@ function requestBody(messages: ChatMessage[], stream: boolean) {
   }
 }
 
+/**
+ * 非流式调用的超时。fetch 默认不超时，AI 侧一挂就会把 worker 的并发位一直占着，
+ * 学生那边的按钮也就一直转。流式调用不设：那边超时会把正在推的长回答直接掐断，
+ * 客户端断开本来就能收尾。
+ */
+const COMPLETE_TIMEOUT_MS = 60_000
+
 export async function completeChat(system: string, user: string) {
   if (!config.aiKey) throw new Error("缺少 AI_KEY")
   const response = await fetch(new URL("/chat/completions", config.aiBaseUrl), {
     method: "POST",
+    signal: AbortSignal.timeout(COMPLETE_TIMEOUT_MS),
     headers: { "content-type": "application/json", authorization: `Bearer ${config.aiKey}` },
     body: JSON.stringify(requestBody([
       { role: "system", content: system },
diff --git a/apps/api/src/worker.ts b/apps/api/src/worker.ts
index 60e6daa..5592b0c 100644
--- a/apps/api/src/worker.ts
+++ b/apps/api/src/worker.ts
@@ -18,7 +18,11 @@ const worker = new Worker<JudgeJobData>(
 
 const flowchartWorker = new Worker<FlowchartJobData>(
   flowchartQueueName,
-  async (job) => evaluateFlowchart(job.data),
+  // attemptsMade 是「此前已经失败过几次」，当前这次还没计进去，
+  // 所以最后一次尝试的判据是 attemptsMade + 1 >= attempts
+  async (job) => evaluateFlowchart(job.data, {
+    isFinalAttempt: job.attemptsMade + 1 >= (job.opts.attempts ?? 1),
+  }),
   { connection: createBlockingRedis(), concurrency: 2 },
 )