fix: The output of the parser in the ingestion pipeline contains HTML tags (#14920)

## Summary
This change fixes ingestion quality issues where MinerU parser output
may contain HTML fragments (for example, table-related tags like `<tr>`,
`<td>`, `<br>`), which were previously passed directly into
chunking/tokenization and degraded chunk quality.

The fix adds a sanitization step in the MinerU parser path so parsed
sections are normalized to clean text before chunking.

## Change Type (select all)
- [x] Bug fix
- [x] Ingestion pipeline improvement
- [x] Parser/chunking quality fix

## Related Issue
- https://github.com/infiniflow/ragflow/issues/14831

test/unit_test/deepdoc/parser/test_mineru_parser.py

@@ -0,0 +1,68 @@
+import importlib.util
+import logging
+import sys
+from pathlib import Path
+from types import ModuleType
+
+
+def _load_mineru_parser(monkeypatch):
+    repo_root = Path(__file__).resolve().parents[4]
+
+    deepdoc_mod = ModuleType("deepdoc")
+    deepdoc_mod.__path__ = [str(repo_root / "deepdoc")]
+    monkeypatch.setitem(sys.modules, "deepdoc", deepdoc_mod)
+
+    parser_mod = ModuleType("deepdoc.parser")
+    parser_mod.__path__ = [str(repo_root / "deepdoc" / "parser")]
+    monkeypatch.setitem(sys.modules, "deepdoc.parser", parser_mod)
+
+    pdf_parser_mod = ModuleType("deepdoc.parser.pdf_parser")
+
+    class _RAGFlowPdfParser:
+        pass
+
+    pdf_parser_mod.RAGFlowPdfParser = _RAGFlowPdfParser
+    monkeypatch.setitem(sys.modules, "deepdoc.parser.pdf_parser", pdf_parser_mod)
+
+    utils_mod = ModuleType("deepdoc.parser.utils")
+    utils_mod.extract_pdf_outlines = lambda *_args, **_kwargs: []
+    monkeypatch.setitem(sys.modules, "deepdoc.parser.utils", utils_mod)
+
+    module_name = "test_mineru_parser_unit_module"
+    module_path = repo_root / "deepdoc" / "parser" / "mineru_parser.py"
+    spec = importlib.util.spec_from_file_location(module_name, module_path)
+    module = importlib.util.module_from_spec(spec)
+    monkeypatch.setitem(sys.modules, module_name, module)
+    spec.loader.exec_module(module)
+    return module
+
+
+def test_sanitize_section_text_removes_escaped_html_tags(monkeypatch):
+    module = _load_mineru_parser(monkeypatch)
+    text = "<table><tr><td>Alpha</td><td>Beta</td></tr></table>"
+
+    sanitized = module.MinerUParser._sanitize_section_text(text)
+
+    assert sanitized == "AlphaBeta"
+    assert "<td>" not in sanitized
+    assert "</td>" not in sanitized
+
+
+def test_transfer_to_sections_logs_sections_dropped_after_sanitization(monkeypatch, caplog):
+    module = _load_mineru_parser(monkeypatch)
+    parser = module.MinerUParser()
+    outputs = [
+        {
+            "type": module.MinerUContentType.TEXT,
+            "text": "&lt;td&gt;&lt;/td&gt;",
+            "page_idx": 0,
+            "bbox": (0, 0, 1, 1),
+        }
+    ]
+
+    with caplog.at_level(logging.DEBUG, logger=parser.logger.name):
+        sections = parser._transfer_to_sections(outputs, parse_method="pipeline")
+
+    assert sections == []
+    assert "Skip section after sanitization" in caplog.text
+    assert f"type={module.MinerUContentType.TEXT}" in caplog.text