diff --git a/src/lib/domain/__tests__/validation.test.ts b/src/lib/domain/__tests__/validation.test.ts
index c645177..cc069c4 100644
--- a/src/lib/domain/__tests__/validation.test.ts
+++ b/src/lib/domain/__tests__/validation.test.ts
@@ -122,6 +122,24 @@ describe("domain validation", () => {
     expect(parsed.ai_taste_checks[0]?.rule_id).toBe("promotion_tone");
   });
 
+  it("normalizes empty AI taste check evidence from LLM copy results", () => {
+    const parsed = copyOptimizationResultSchema.parse({
+      optimized_text: "我把句子顺了一下。",
+      change_notes: [],
+      ai_taste_checks: [
+        {
+          rule_id: "promotion_tone",
+          status: "pass",
+          evidence: "",
+          suggestion: "",
+        },
+      ],
+      warnings: [],
+    });
+
+    expect(parsed.ai_taste_checks[0]?.evidence).toBe("未提供具体证据。");
+  });
+
   it("accepts an unconfirmed optimization fact card with unresolved items", () => {
     const parsed = optimizationFactCardSchema.parse({
       company_full_name: "",
diff --git a/src/lib/domain/validation.ts b/src/lib/domain/validation.ts
index c4198b1..8105c3a 100644
--- a/src/lib/domain/validation.ts
+++ b/src/lib/domain/validation.ts
@@ -217,6 +217,14 @@ const optionalLlmStringSchema = z.preprocess((value) => {
   return normalizeStringValue(value);
 }, z.string().trim().default(""));
 
+const fallbackLlmEvidenceSchema = z.preprocess((value) => {
+  const normalized = normalizeStringValue(value);
+  if (typeof normalized === "string" && normalized.trim().length === 0) {
+    return "未提供具体证据。";
+  }
+  return normalized;
+}, z.string().trim().min(1));
+
 const stringListSchema = z.preprocess(
   normalizeStringList,
   z.array(z.string().trim().min(1)).default([]),
@@ -480,7 +488,7 @@ const copyAiTasteCheckSchema = z.object({
     "filler_hedging",
   ]),
   status: z.enum(["pass", "warn"]),
-  evidence: requiredLlmStringSchema,
+  evidence: fallbackLlmEvidenceSchema,
   suggestion: optionalLlmStringSchema,
 }) satisfies z.ZodType<CopyAiTasteCheck>;