diff --git a/src/video_transcript_api/llm/processors/notes_processor.py b/src/video_transcript_api/llm/processors/notes_processor.py
index 2b8022a4..a4db9a67 100644
--- a/src/video_transcript_api/llm/processors/notes_processor.py
+++ b/src/video_transcript_api/llm/processors/notes_processor.py
@@ -548,15 +548,6 @@ def call_notes(user_prompt: str) -> str:
                     chapter_notes = retry_notes
                 return f"{_format_chapter_heading(chapter)}\n{chapter_notes.strip()}"
 
-            if not mapping.slices:
-                return NotesResult(
-                    text=None,
-                    status=NotesStatus.FAILED,
-                    error=mapping.error or "no chapter slices available",
-                    fingerprint=mapping.current_fingerprint,
-                    chapter_count=0,
-                )
-
             max_workers = min(len(mapping.slices), self.config.notes_concurrency)
             with ThreadPoolExecutor(max_workers=max_workers) as executor:
                 future_positions = {
diff --git a/tests/README.md b/tests/README.md
index e4302d9d..aab0226e 100644
--- a/tests/README.md
+++ b/tests/README.md
@@ -166,7 +166,7 @@ ffprobe / ffmpeg、无预置 fixture、没有 skip 分支。拒绝路径的完
 需要真实 ffprobe 的文件覆盖。
 
 LLM 处理器空输入守卫（#179）：`tests/unit/test_empty_input_processors.py`。
-锁的不变量：`PlainTextProcessor._calibrate_segments`、`SpeakerAwareProcessor._calibrate_chunks` 与 `NotesProcessor.process` 在输入分段/分块列表为空时直接返回与空输入同构的空结果，不启动 `ThreadPoolExecutor(max_workers=0)`，不发起 LLM 调用；端到端空文本/空对话校对返回诚实状态 `calibration_status=none` 且不抛 `ValueError`。
+锁的不变量：`PlainTextProcessor._calibrate_segments` 与 `SpeakerAwareProcessor._calibrate_chunks` 在输入分段/分块列表为空时直接返回与空输入同构的空结果，不启动 `ThreadPoolExecutor(max_workers=0)`，不发起 LLM 调用；`NotesProcessor.process` 在空 chapters payload 下走 `is_valid` 校验失败返回 `FAILED`，不发起 LLM 调用；端到端空文本/空对话校对返回诚实状态 `calibration_status=none` 且不抛 `ValueError`。
 
 ## 并发压测
 
diff --git a/tests/unit/test_empty_input_processors.py b/tests/unit/test_empty_input_processors.py
index a7412eae..78a1ba42 100644
--- a/tests/unit/test_empty_input_processors.py
+++ b/tests/unit/test_empty_input_processors.py
@@ -9,8 +9,8 @@
    zeroed calibration stats without launching a ThreadPoolExecutor.
 4. SpeakerAwareProcessor.process(dialogs=[]) completes cleanly with empty output
    and honest calibration_status=none.
-5. NotesProcessor with empty chapter slices returns a failed NotesResult rather
-   than crashing on max_workers=0.
+5. NotesProcessor with empty chapters returns a failed NotesResult via
+   is_valid validation failure without issuing LLM calls.
 """
 
 from unittest.mock import MagicMock, Mock
@@ -112,6 +112,41 @@ def test_plain_text_process_empty_text(self, mock_config):
         assert stats["calibration_status"] == CalibrationStatus.NONE
         llm_client.call.assert_not_called()
 
+    def test_plain_text_process_whitespace_only_text(self, mock_config):
+        llm_client = Mock()
+        key_info_mock = Mock(spec=KeyInfo)
+        key_info_mock.to_dict.return_value = {}
+        key_info_mock.format_for_prompt.return_value = ""
+        key_info_extractor = Mock()
+        key_info_extractor.extract.return_value = key_info_mock
+
+        processor = PlainTextProcessor(
+            config=mock_config,
+            llm_client=llm_client,
+            key_info_extractor=key_info_extractor,
+            quality_validator=Mock(),
+        )
+
+        result = processor.process(
+            text=" \t\n",
+            title="Whitespace Recording",
+            author="Author",
+            description="",
+            platform="test",
+            media_id="m1_whitespace",
+        )
+
+        assert result["calibrated_text"] == ""
+        stats = result["stats"]
+        assert stats["original_length"] == len(" \t\n")
+        assert stats["calibrated_length"] == 0
+        assert stats["segment_count"] == 0
+        assert stats["total_segments"] == 0
+        assert stats["calibrated_segments"] == 0
+        assert stats["fallback_segments"] == 0
+        assert stats["calibration_status"] == CalibrationStatus.NONE
+        llm_client.call.assert_not_called()
+
     def test_speaker_aware_calibrate_chunks_empty_input(self, mock_config):
         llm_client = Mock()
         processor = SpeakerAwareProcessor(
@@ -174,7 +209,8 @@ def test_speaker_aware_process_empty_dialogs(self, mock_config):
         assert stats["calibration_stats"]["calibration_status"] == CalibrationStatus.NONE
         llm_client.call.assert_not_called()
 
-    def test_notes_processor_empty_slices_returns_failed_result(self, mock_config):
+    def test_notes_processor_empty_chapters_fails_validation(self, mock_config):
+        # 空 chapters -> map_notes_chapter_slices 校验失败 -> is_valid=False -> FAILED，非 slices 空守卫路径
         llm_client = Mock()
         processor = NotesProcessor(llm_client, mock_config)