fix: pipeline LLM 全失败时明确报错而非静默输出空 IR - Closes #15

- step1: 所有 LLM 调用返回空 function_units 时抛出 RuntimeError
- step1: main() 在 _quick_validate 未通过时 sys.exit(1)
- step2: function_units 为空时提前报错终止
- step3: fragments 为空时提前报错终止
- test: test_step1 捕获 SystemExit, test_step2_5/step3 空数据改为 skip

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

skills/ir_generation_skill/step1_semantic_index.py

@@ -632,6 +632,18 @@ def run_ensemble_semantic_index(doc: dict) -> dict:
     if not raw_results:
         raise RuntimeError("所有集成的 LLM 调用均失败")
 
+    # Check that at least some raw results have function_units
+    all_empty = all(
+        len(r[2].get("function_units", [])) == 0 for r in raw_results
+    )
+    if all_empty:
+        raise RuntimeError(
+            "所有集成的 LLM 调用返回了空的 function_units。请检查:\n"
+            "  1. API Key 是否配置正确 (secrets.yaml 或环境变量)\n"
+            "  2. 输入文档格式是否与 Prompt 兼容\n"
+            "  3. LLM 服务是否可访问"
+        )
+
     # Sort by temperature for determinism
     raw_results.sort(key=lambda x: x[1])
     semantic_indices = [r[2] for r in raw_results]
@@ -709,6 +721,17 @@ def main():
     n_concepts = cs.get("total_concepts", len(merged_index.get("concepts", [])))
     n_units = cs.get("total_units", len(merged_index.get("function_units", [])))
     n_versions = merged_index.get("ensemble_versions", len(config.ENSEMBLE_TEMPERATURES))
+
+    if not merged_index.get("validation_passed", True):
+        print(f"\n错误: 语义索引验证未通过!")
+        gaps = merged_index.get("validation_gaps", {})
+        for category, issues in gaps.items():
+            for issue in issues:
+                print(f"  [{category}] {issue}")
+        print(f"\n流水线中止: {n_units} 个功能单元不满足最低覆盖率要求。")
+        print("请检查 LLM 配置、输入文档格式和 Prompt 兼容性。")
+        sys.exit(1)
+
     print(f"\n完成! {n_versions} 版本集成, {n_concepts} 个概念, {n_units} 个功能单元.")
     print(f"输出: {config.SEMANTIC_INDEX_JSON}")