fix(rectification): fall back when narrative models fail

docs/BUG_HISTORY.md

@@ -1444,3 +1444,18 @@
 - 防复发：跨语言 wire schema 必须覆盖 Python 真源可返回的枚举；诊断状态在适配边界归一化，内部领域模型继续保持最小稳定集合。
 - 相关记录：BUG-067、BUG-075
 - 修复版本：本次修复提交
+
+## BUG-078 | 叙事模型超时导致已完成的事件评分整轮返回 503
+
+- 状态：resolved
+- 首次发现：2026-07-26
+- 最近更新：2026-07-26
+- 影响面：生时校正开放叙事、历史事件保存、候选收敛、Narrative Agent 降级路径
+- 用户现象：历史事件已被成功抽取和技术评分，但主叙事模型与备用模型超时后，整轮返回 503，用户必须重试且无法看到已记录结果。
+- 触发条件：非最终轮的两次叙事生成均超时、报错或未通过安全校验。
+- 根因：安全的 packet 驱动兜底已经存在，却只允许最终轮使用；首轮和中间轮在两次生成失败后直接抛出 `RectificationNarrativeUnavailable`，把非关键的文案依赖变成了事件记录与收敛的硬依赖。
+- 修复：所有阶段在两次生成失败后统一使用既有的确定性安全兜底；保留已完成的事件记录、技术评分与候选推进，`evidenceRequest` 为 null，不机械追问，也不展示模型未验证内容。
+- 验证：回归覆盖首轮超时、首轮非法问卷、首轮非法技术层和中间轮虚构引用，均返回安全兜底且不泄漏被拒内容；Narrative Agent 聚焦测试、目标 ESLint、生产构建与 `git diff --check` 通过。
+- 防复发：叙事模型只能影响自然语言表达，不能成为事件持久化和确定性收敛的单点故障；降级输出必须来自已验证 packet。
+- 相关记录：BUG-067、BUG-075、BUG-077
+- 修复版本：本次修复提交

frontend/src/lib/conversational-rectification/narrative-agent.ts

@@ -784,17 +784,6 @@ export async function generateRectificationNarrative(input: {
       issues = [...issues, ...attemptIssues];
     }
   }
-  if (input.phase !== "final") {
-    logNarrativeGeneration({
-      phase: input.phase,
-      retryCount: 1,
-      fallbackUsed: false,
-      source: "failed",
-      issues: boundedReceiptIssues(issues),
-      startedAt,
-    });
-    throw new Error("RectificationNarrativeUnavailable");
-  }
   const output = fallbackOutput(input.packet, input.phase);
   const narrative = input.phase === "final"
     ? appendFinalAnalysisTables(output.narrative, input.packet, input.context ?? {})

frontend/tests/conversational-narrative-agent.test.ts

@@ -569,7 +569,7 @@ test("allows packet-grounded technical tables during an intermediate turn", () =
   assert.deepEqual(validateNarrativeAgainstPacket(output, packet, "intermediate"), { valid: true, issues: [] });
 });
 
-test("rejects a generic broad-year choice questionnaire without replacing the first Agent answer with a template", async () => {
+test("replaces a generic broad-year choice questionnaire with the safe fallback", async () => {
   const invalid = {
     ...richOutput(),
     narrative: [
@@ -588,14 +588,14 @@ test("rejects a generic broad-year choice questionnaire without replacing the fi
   assert.equal(direct.valid, false);
   assert.ok(direct.issues.some((issue) => issue.includes("broad-year choice questionnaire")));
 
-  await assert.rejects(
-    generateRectificationNarrative({
-      phase: "first",
-      packet: syntheticTechnicalPacket(),
-      generator: generator([invalid, invalid]),
-    }),
-    /RectificationNarrativeUnavailable/,
-  );
+  const result = await generateRectificationNarrative({
+    phase: "first",
+    packet: syntheticTechnicalPacket(),
+    generator: generator([invalid, invalid]),
+  });
+  assert.equal(result.fallbackUsed, true);
+  assert.equal(result.output.evidenceRequest, null);
+  assert.doesNotMatch(result.narrative, /2018–2020/);
 });
 
 test("rejects generic individual-year options even without a written range", () => {
@@ -1030,52 +1030,49 @@ test("records first-turn generation timeouts separately from schema failures", a
   const warnings: string[] = [];
   const originalWarn = console.warn;
   console.warn = (...values: unknown[]) => warnings.push(values.map(String).join(" "));
+  let result: Awaited<ReturnType<typeof generateRectificationNarrative>>;
   try {
-    await assert.rejects(
-      generateRectificationNarrative({
-        phase: "first",
-        packet: syntheticTechnicalPacket(),
-        generator: {
-          modelId: "test-model",
-          async generate() { throw new DOMException("timed out", "TimeoutError"); },
-        },
-      }),
-      /RectificationNarrativeUnavailable/,
-    );
+    result = await generateRectificationNarrative({
+      phase: "first",
+      packet: syntheticTechnicalPacket(),
+      generator: {
+        modelId: "test-model",
+        async generate() { throw new DOMException("timed out", "TimeoutError"); },
+      },
+    });
   } finally {
     console.warn = originalWarn;
   }
 
+  assert.equal(result.fallbackUsed, true);
   assert.match(warnings.at(-1) ?? "", /"issueCodes":\["timeout"\]/);
 });
 
-test("rejects the first turn instead of presenting a deterministic template as an agent answer", async () => {
+test("falls back safely when the first-turn model output is invalid", async () => {
   const packet = syntheticTechnicalPacket();
   const invalid = { ...richOutput(), sensitiveLayers: ["D60"] };
-  await assert.rejects(
-    generateRectificationNarrative({
-      phase: "first",
-      packet,
-      generator: generator([invalid, invalid]),
-    }),
-    /RectificationNarrativeUnavailable/,
-  );
+  const result = await generateRectificationNarrative({
+    phase: "first",
+    packet,
+    generator: generator([invalid, invalid]),
+  });
+  assert.equal(result.fallbackUsed, true);
+  assert.doesNotMatch(result.narrative, /D60/);
 });
 
-test("rejects an invalid intermediate narrative instead of showing a deterministic template", async () => {
+test("falls back safely when an intermediate narrative is invalid", async () => {
   const inventedReference = `invented-${"x".repeat(500)}`;
   const invalid = {
     ...richOutput(),
     narrative: `${richOutput().narrative}\n另见【${inventedReference}】。`,
   };
-  await assert.rejects(
-    generateRectificationNarrative({
-      phase: "intermediate",
-      packet: syntheticTechnicalPacket(),
-      generator: generator([invalid, invalid]),
-    }),
-    /RectificationNarrativeUnavailable/,
-  );
+  const result = await generateRectificationNarrative({
+    phase: "intermediate",
+    packet: syntheticTechnicalPacket(),
+    generator: generator([invalid, invalid]),
+  });
+  assert.equal(result.fallbackUsed, true);
+  assert.doesNotMatch(result.narrative, /invented-/);
 });
 
 test("builds distinct first, intermediate, and final grounded prompts", async () => {