From 626c850ccb2c25be92a9ce575886a85f54e8683a Mon Sep 17 00:00:00 2001
From: jinliyl <6469360+jinliyl@users.noreply.github.com>
Date: Mon, 24 Aug 2026 18:59:53 +0800
Subject: [PATCH 1/2] fix(daily-paper): sanitize Unicode surrogates (#487)

* fix(daily-paper): sanitize Unicode surrogates

* fix(daily-paper): sanitize analysis workflow state
---
 reme/steps/cookbook/daily_paper/_common.py | 28 +++++++-
 reme/steps/cookbook/daily_paper/analyze.py | 13 ++--
 tests/unit/test_daily_paper.py             | 81 +++++++++++++++++++++-
 3 files changed, 111 insertions(+), 11 deletions(-)

diff --git a/reme/steps/cookbook/daily_paper/_common.py b/reme/steps/cookbook/daily_paper/_common.py
index 7d8dcd33..72ec0a90 100644
--- a/reme/steps/cookbook/daily_paper/_common.py
+++ b/reme/steps/cookbook/daily_paper/_common.py
@@ -22,6 +22,7 @@ _FRONTMATTER_PATTERN = re.compile(r"^---\s*\n.*?\n---\s*\n", re.DOTALL)
 _MARKDOWN_HEADING_PATTERN = re.compile(r"^#+\s*")
 _UNSAFE_FILENAME_CHARS = re.compile(r'[<>:"/\\|?*\x00-\x1f]')
 _CHINESE_PATTERN = re.compile(r"[\u3400-\u4dbf\u4e00-\u9fff]")
+_SURROGATE_PATTERN = re.compile(r"[\ud800-\udfff]")
 _OutputT = TypeVar("_OutputT", bound=BaseModel)
 
 
@@ -36,9 +37,28 @@ def strip_frontmatter(body: str) -> str:
     return _FRONTMATTER_PATTERN.sub("", body.strip(), count=1).strip()
 
 
+def replace_surrogates(value: str) -> str:
+    """Replace invalid Unicode surrogate code points with replacement characters."""
+    return _SURROGATE_PATTERN.sub("\ufffd", value)
+
+
+def _replace_surrogates_recursive(value: Any) -> Any:
+    """Replace surrogates in strings nested in frontmatter metadata."""
+    if isinstance(value, str):
+        return replace_surrogates(value)
+    if isinstance(value, dict):
+        return {_replace_surrogates_recursive(key): _replace_surrogates_recursive(item) for key, item in value.items()}
+    if isinstance(value, list):
+        return [_replace_surrogates_recursive(item) for item in value]
+    if isinstance(value, tuple):
+        return tuple(_replace_surrogates_recursive(item) for item in value)
+    return value
+
+
 def normalize_chinese_title(raw: str, fallback: str) -> str:
     """Return one safe Chinese title that can also be used as the filename stem."""
-    title = _MARKDOWN_HEADING_PATTERN.sub("", str(raw or "").strip())
+    title = replace_surrogates(str(raw or "").strip())
+    title = _MARKDOWN_HEADING_PATTERN.sub("", title)
     if title.lower().endswith(".md"):
         title = title[:-3]
     title = _UNSAFE_FILENAME_CHARS.sub("-", title)
@@ -92,7 +112,7 @@ async def write_atomic(path: Path, content: str | bytes) -> None:
     lock = await get_path_lock(path)
     async with lock:
         temp_path = path.with_name(f".{path.name}.{uuid4().hex}.tmp")
-        payload = content.encode("utf-8") if isinstance(content, str) else content
+        payload = replace_surrogates(content).encode("utf-8") if isinstance(content, str) else content
         try:
             async with aiofiles.open(temp_path, "wb") as stream:
                 await stream.write(payload)
@@ -104,7 +124,9 @@ async def write_atomic(path: Path, content: str | bytes) -> None:
 
 async def write_markdown(path: Path, body: str, metadata: dict[str, Any]) -> None:
     """Serialize a frontmatter Markdown document atomically."""
-    rendered = frontmatter.dumps(frontmatter.Post(body.strip(), **metadata))
+    safe_body = replace_surrogates(body).strip()
+    safe_metadata = _replace_surrogates_recursive(metadata)
+    rendered = frontmatter.dumps(frontmatter.Post(safe_body, **safe_metadata))
     await write_atomic(path, rendered if rendered.endswith("\n") else f"{rendered}\n")
 
 
diff --git a/reme/steps/cookbook/daily_paper/analyze.py b/reme/steps/cookbook/daily_paper/analyze.py
index 6d1f177b..68e3579f 100644
--- a/reme/steps/cookbook/daily_paper/analyze.py
+++ b/reme/steps/cookbook/daily_paper/analyze.py
@@ -12,6 +12,7 @@ from ._common import (
     DailyPaperStep,
     iter_note_metadata,
     normalize_chinese_title,
+    replace_surrogates,
     resolve_unique_note_path,
     strip_frontmatter,
     structured_output,
@@ -43,7 +44,8 @@ class DailyPaperAnalyzeStep(DailyPaperStep):
         page_count = min(len(reader.pages), max_pages)
         truncated = len(reader.pages) > max_pages
         for page_number, page in enumerate(reader.pages[:page_count], start=1):
-            block = f"\n\n--- PAGE {page_number} ---\n\n{(page.extract_text() or '').strip()}"
+            page_text = replace_surrogates((page.extract_text() or "").strip())
+            block = f"\n\n--- PAGE {page_number} ---\n\n{page_text}"
             if size + len(block) > max_chars:
                 if (remaining := max_chars - size) > 0:
                     chunks.append(block[:remaining])
@@ -126,8 +128,9 @@ class DailyPaperAnalyzeStep(DailyPaperStep):
         )
         used_titles.add(title)
         note_rel = note_path.relative_to(self.workspace_path).as_posix()
-        body = strip_frontmatter(output.body)
-        if not output.desc.strip() or not body:
+        desc = replace_surrogates(output.desc.strip())
+        body = replace_surrogates(strip_frontmatter(output.body))
+        if not desc or not body:
             raise ValueError(f"Agent returned an empty paper note for {paper.arxiv_id}")
         await write_markdown(
             note_path,
@@ -135,7 +138,7 @@ class DailyPaperAnalyzeStep(DailyPaperStep):
             {
                 "name": title,
                 "title": title,
-                "description": output.desc.strip(),
+                "description": desc,
                 "kind": "daily-paper-analysis",
                 "arxiv_id": paper.arxiv_id,
                 "source_title": paper.title,
@@ -163,7 +166,7 @@ class DailyPaperAnalyzeStep(DailyPaperStep):
             arxiv_id=paper.arxiv_id,
             reasoning=selected.reasoning,
             title=title,
-            desc=output.desc.strip(),
+            desc=desc,
             body=body,
             note_path=note_rel,
             pdf_path=pdf_rel,
diff --git a/tests/unit/test_daily_paper.py b/tests/unit/test_daily_paper.py
index e0a027a3..851a93da 100644
--- a/tests/unit/test_daily_paper.py
+++ b/tests/unit/test_daily_paper.py
@@ -25,6 +25,12 @@ from reme.steps.cookbook.daily_paper import (
     DailyPaperSelectStep,
 )
 from reme.steps.cookbook.daily_paper import analyze, collect
+from reme.steps.cookbook.daily_paper._common import (
+    normalize_chinese_title,
+    replace_surrogates,
+    write_atomic,
+    write_markdown,
+)
 from reme.steps.cookbook.daily_paper.rank import build_candidate_pool, rrf_score
 from reme.steps.cookbook.dingtalk import DingTalkMarkdownSendStep
 from reme.steps.cookbook.dingtalk import send as dingtalk_send
@@ -57,6 +63,73 @@ def _paper(arxiv_id: str, *, title: str = "Paper", upvotes: int = 10) -> PaperIn
     )
 
 
+def test_daily_paper_replaces_surrogates_in_text_and_titles():
+    """Invalid surrogate code points become visible replacement characters."""
+    assert replace_surrogates("before\ud800middle\udfffafter") == "before\ufffdmiddle\ufffdafter"
+    assert normalize_chinese_title("论文\ud800标题", "fallback") == "论文\ufffd标题"
+
+
+@pytest.mark.asyncio
+async def test_daily_paper_atomic_write_replaces_surrogates(tmp_path: Path):
+    """Markdown writes always produce valid UTF-8 even when model output is malformed."""
+    target = tmp_path / "note.md"
+
+    await write_atomic(target, "before\ud800after")
+
+    assert target.read_text(encoding="utf-8") == "before\ufffdafter"
+
+
+@pytest.mark.asyncio
+async def test_daily_paper_markdown_write_replaces_surrogates_in_frontmatter(tmp_path: Path):
+    """Frontmatter serialization sanitizes nested metadata before YAML encoding."""
+    target = tmp_path / "note.md"
+
+    await write_markdown(
+        target,
+        "body\ud800text",
+        {"description": "meta\udffftext", "authors": ["safe", "author\ud800name"]},
+    )
+
+    post = frontmatter.load(target)
+    assert post.content == "body\ufffdtext"
+    assert post.metadata == {
+        "description": "meta\ufffdtext",
+        "authors": ["safe", "author\ufffdname"],
+    }
+
+
+def test_daily_paper_pdf_extraction_replaces_surrogates(monkeypatch, tmp_path: Path):
+    """Malformed PDF text is sanitized before it enters an agent prompt."""
+
+    class FakePage:
+        """Return text containing one unpaired surrogate."""
+
+        @staticmethod
+        def extract_text():
+            """Return the malformed page text."""
+            return "before\ud800after"
+
+    class FakeReader:
+        """Expose one fake PDF page."""
+
+        def __init__(self, _path: str):
+            self.pages = [FakePage()]
+
+    import pypdf
+
+    monkeypatch.setattr(pypdf, "PdfReader", FakeReader)
+
+    content, page_count, truncated = DailyPaperAnalyzeStep._extract_pdf_text_sync(  # pylint: disable=protected-access
+        tmp_path / "paper.pdf",
+        20,
+        300_000,
+    )
+
+    assert content == "--- PAGE 1 ---\n\nbefore\ufffdafter"
+    assert page_count == 1
+    assert truncated is False
+
+
 def test_hf_payload_and_html_normalization():
     """HF list/detail shapes normalize and HTML rank order de-duplicates."""
     payload = {
@@ -705,8 +778,8 @@ async def test_pipeline_filters_strict_yesterday_and_writes_outputs(
             },
             {
                 "title": "记忆代理研究",
-                "desc": "Detailed note one",
-                "body": "Evidence one [p. 1].",
+                "desc": "Detailed note\ud800 one",
+                "body": "Evidence\udfff one [p. 1].",
             },
             {
                 "title": "上下文压缩研究",
@@ -801,7 +874,9 @@ async def test_pipeline_filters_strict_yesterday_and_writes_outputs(
     assert "ReMe" not in analysis_prompt
     assert "# PDF 分页文本" in analysis_prompt
     digest_prompt = cc_wrapper.calls[-1]["inputs"]
-    assert "Evidence one [p. 1]." in digest_prompt
+    assert "Evidence\ufffd one [p. 1]." in digest_prompt
+    assert "Detailed note\ufffd one" in digest_prompt
+    assert not any("\ud800" <= character <= "\udfff" for character in digest_prompt)
     assert "调用 Read" not in digest_prompt
     assert "daily/2026-07-21" not in digest_prompt
     assert "长期记忆" not in digest_prompt

From 15d12be6b678ff11fbb16d93c70c7082d47816f2 Mon Sep 17 00:00:00 2001
From: jinliyl <6469360+jinliyl@users.noreply.github.com>
Date: Wed, 26 Aug 2026 16:16:26 +0800
Subject: [PATCH 2/2] fix(index): tolerate invalid text encoding (#490)

* fix(index): tolerate invalid text encoding

* fix(index): preserve text chunker compatibility
---
 docs/en/memory_as_file.md                     |  5 +
 docs/zh/memory_as_file.md                     |  4 +
 .../file_chunker/default_file_chunker.py      | 44 ++++++++-
 .../file_chunker/markdown_file_chunker.py     | 14 ++-
 tests/unit/test_default_file_chunker.py       | 63 ++++++++++++
 tests/unit/test_markdown_file_chunker.py      | 98 +++++++++++++++++++
 6 files changed, 222 insertions(+), 6 deletions(-)

diff --git a/docs/en/memory_as_file.md b/docs/en/memory_as_file.md
index 5202887a..f519396a 100644
--- a/docs/en/memory_as_file.md
+++ b/docs/en/memory_as_file.md
@@ -388,3 +388,8 @@ This lets the agent see not only an isolated paragraph but also its structural p
 
 Non-Markdown files use `DefaultFileChunker` by default. It splits by byte size and preserves a small overlap. For
 Markdown, the chunker also avoids cutting `[[wikilinks]]` in the middle.
+
+`DefaultFileChunker` and `MarkdownFileChunker` decode files with their configured `encoding` and normalize platform
+newlines to LF before indexing. Their default `invalid_encoding_policy: replace` keeps decodable content searchable
+when a source contains invalid bytes, without modifying the source file. Set `invalid_encoding_policy: strict` on a
+chunker component to reject such files instead.
diff --git a/docs/zh/memory_as_file.md b/docs/zh/memory_as_file.md
index f9532d42..6d792ed9 100644
--- a/docs/zh/memory_as_file.md
+++ b/docs/zh/memory_as_file.md
@@ -363,3 +363,7 @@ FileChunk[]
 这样检索命中时，Agent 不只看到孤立段落，还能看到它在原文件中的结构位置。
 
 非 Markdown 默认走 `DefaultFileChunker`：按字节大小切分，并保留少量 overlap；对 Markdown 则会避免把 `[[wikilink]]` 从中间切开。
+
+`DefaultFileChunker` 和 `MarkdownFileChunker` 使用各自配置的 `encoding` 解码文件，并在索引前将平台换行符统一为
+LF。默认的 `invalid_encoding_policy: replace` 会在源文件含无效字节时保留其中可解码的内容用于检索，但不会修改源
+文件；如需拒绝此类文件，可在 chunker 组件上设置 `invalid_encoding_policy: strict`。
diff --git a/reme/components/file_chunker/default_file_chunker.py b/reme/components/file_chunker/default_file_chunker.py
index 23457f5b..4fddc632 100644
--- a/reme/components/file_chunker/default_file_chunker.py
+++ b/reme/components/file_chunker/default_file_chunker.py
@@ -2,6 +2,7 @@
 
 from bisect import bisect_right
 from pathlib import Path
+from typing import Literal
 
 import aiofiles
 import yaml
@@ -11,14 +12,29 @@ from ..component_registry import R
 from ...schema import FileChunk, FileFrontMatter, FileNode
 from ...utils.wikilink_handler import WikilinkHandler
 
+InvalidEncodingPolicy = Literal["replace", "strict"]
+
 
 @R.register("default")
 class DefaultFileChunker(BaseFileChunker):
     """Default chunker that splits files into byte-based overlapping chunks."""
 
-    def __init__(self, encoding: str = "utf-8", chunk_byte_size: int = 10000, overlap_byte_size: int = 100, **kwargs):
+    def __init__(
+        self,
+        encoding: str = "utf-8",
+        chunk_byte_size: int = 10000,
+        overlap_byte_size: int = 100,
+        *,
+        invalid_encoding_policy: InvalidEncodingPolicy = "replace",
+        **kwargs,
+    ):
         super().__init__(**kwargs)
+        if invalid_encoding_policy not in {"replace", "strict"}:
+            raise ValueError(
+                f"invalid_encoding_policy must be 'replace' or 'strict', got {invalid_encoding_policy!r}",
+            )
         self.encoding = encoding
+        self.invalid_encoding_policy = invalid_encoding_policy
         self.chunk_byte_size = max(100, chunk_byte_size)
         self.overlap_byte_size = max(4, overlap_byte_size)
 
@@ -37,13 +53,35 @@ class DefaultFileChunker(BaseFileChunker):
             front_matter = FileFrontMatter()
         return front_matter, text[end_idx + 4 :].lstrip("\n")
 
+    async def _read_text_for_indexing(self, file_path: Path) -> str:
+        """Decode text for a derived index without modifying the source file."""
+        async with aiofiles.open(file_path, "rb") as f:
+            data = await f.read()
+        try:
+            text = data.decode(self.encoding)
+        except UnicodeDecodeError as exc:
+            if self.invalid_encoding_policy == "strict":
+                raise
+            invalid_bytes = data[exc.start : exc.end].hex(" ")
+            self.logger.warning(
+                f"Invalid {self.encoding} in {file_path} at byte {exc.start} (bytes: {invalid_bytes}); "
+                "indexed with replacement characters; source file unchanged",
+            )
+            text = data.decode(self.encoding, errors="replace")
+            # Some codecs (for example ASCII) cannot encode U+FFFD. Convert the
+            # decoded fallback to that codec's own replacement representation so
+            # later byte-based chunking remains safe.
+            text = text.encode(self.encoding, errors="replace").decode(self.encoding)
+
+        # Match the universal-newline behavior of the previous text-mode reads.
+        return text.replace("\r\n", "\n").replace("\r", "\n")
+
     async def chunk(self, path: str | Path) -> tuple[FileNode, list[FileChunk]]:
         file_path = Path(path)
         stat = file_path.stat()
         rel_path = self.to_workspace_relative(path)
 
-        async with aiofiles.open(file_path, encoding=self.encoding) as f:
-            text = await f.read()
+        text = await self._read_text_for_indexing(file_path)
 
         if not text:
             return FileNode(path=rel_path, st_mtime=stat.st_mtime), []
diff --git a/reme/components/file_chunker/markdown_file_chunker.py b/reme/components/file_chunker/markdown_file_chunker.py
index 7da94ae6..06a07793 100644
--- a/reme/components/file_chunker/markdown_file_chunker.py
+++ b/reme/components/file_chunker/markdown_file_chunker.py
@@ -24,7 +24,7 @@ import yaml
 from pydantic import ValidationError
 
 
-from .default_file_chunker import DefaultFileChunker
+from .default_file_chunker import DefaultFileChunker, InvalidEncodingPolicy
 from ..component_registry import R
 from ...schema import (
     FileChunk,
@@ -108,9 +108,16 @@ class MarkdownFileChunker(DefaultFileChunker):
         max_ast_sections: int | None = 100,
         include_frontmatter_in_metadata: bool = False,
         include_frontmatter_keys_in_metadata: list[str] | None = None,
+        *,
+        invalid_encoding_policy: InvalidEncodingPolicy = "replace",
         **kwargs,
     ):
-        super().__init__(encoding=encoding, chunk_byte_size=chunk_byte_size, **kwargs)
+        super().__init__(
+            encoding=encoding,
+            invalid_encoding_policy=invalid_encoding_policy,
+            chunk_byte_size=chunk_byte_size,
+            **kwargs,
+        )
         self.embed_toc = embed_toc
         self.max_ast_sections = max(0, max_ast_sections) if max_ast_sections is not None else None
         self.include_frontmatter_in_metadata = include_frontmatter_in_metadata
@@ -119,7 +126,8 @@ class MarkdownFileChunker(DefaultFileChunker):
     async def chunk(self, path: str | Path) -> tuple[FileNode, list[FileChunk]]:
         file_path = Path(path)
         rel_path = self.to_workspace_relative(path)
-        front_matter, content, line_offset = self._parse_front_matter(file_path.read_text(encoding=self.encoding))
+        text = await self._read_text_for_indexing(file_path)
+        front_matter, content, line_offset = self._parse_front_matter(text)
 
         chunks: list[FileChunk] = []
         if content and content.strip():
diff --git a/tests/unit/test_default_file_chunker.py b/tests/unit/test_default_file_chunker.py
index bf22d77e..aebd19ba 100644
--- a/tests/unit/test_default_file_chunker.py
+++ b/tests/unit/test_default_file_chunker.py
@@ -97,6 +97,69 @@ def test_parse_with_custom_encoding():
     asyncio.run(run())
 
 
+def test_invalid_encoding_policy_is_validated():
+    """Reject misspelled policies instead of silently changing decoding behavior."""
+    try:
+        DefaultFileChunker(invalid_encoding_policy="ignore")
+    except ValueError as exc:
+        assert "invalid_encoding_policy" in str(exc)
+    else:
+        raise AssertionError("invalid encoding policy must be rejected")
+
+
+def test_constructor_preserves_positional_arguments():
+    """New decoding options must not reinterpret the established positional API."""
+    chunker = DefaultFileChunker("utf-8", 5000, 100)
+
+    assert chunker.encoding == "utf-8"
+    assert chunker.chunk_byte_size == 5000
+    assert chunker.overlap_byte_size == 100
+
+
+def test_newlines_are_normalized_before_chunking():
+    """Binary reads retain the universal-newline behavior of the old text reader."""
+
+    async def run():
+        with tempfile.NamedTemporaryFile(delete=False, suffix=".txt") as f:
+            f.write(b"alpha\r\nbeta\rgamma\n")
+            temp_path = f.name
+
+        try:
+            chunker = DefaultFileChunker()
+            _, original_chunks = await chunker.chunk(temp_path)
+            with open(temp_path, "wb") as f:
+                f.write(b"alpha\nbeta\ngamma\n")
+            _, normalized_chunks = await chunker.chunk(temp_path)
+
+            assert [chunk.text for chunk in original_chunks] == ["alpha\nbeta\ngamma\n"]
+            assert [chunk.id for chunk in original_chunks] == [chunk.id for chunk in normalized_chunks]
+        finally:
+            os.unlink(temp_path)
+
+    asyncio.run(run())
+
+
+def test_ascii_replacement_remains_encodable():
+    """Replacement mode must survive byte-based chunking with a single-byte codec."""
+
+    async def run():
+        source = b"valid\xffinvalid"
+        with tempfile.NamedTemporaryFile(delete=False, suffix=".txt") as f:
+            f.write(source)
+            temp_path = f.name
+
+        try:
+            _, chunks = await DefaultFileChunker(encoding="ascii").chunk(temp_path)
+
+            assert [chunk.text for chunk in chunks] == ["valid?invalid"]
+            with open(temp_path, "rb") as f:
+                assert f.read() == source
+        finally:
+            os.unlink(temp_path)
+
+    asyncio.run(run())
+
+
 def test_parse_links_bare():
     """Bare wikilink: [[target]]."""
     links = WikilinkHandler.extract_links("see [[note]]", "src.md")
diff --git a/tests/unit/test_markdown_file_chunker.py b/tests/unit/test_markdown_file_chunker.py
index 118443ca..fbeeffaf 100644
--- a/tests/unit/test_markdown_file_chunker.py
+++ b/tests/unit/test_markdown_file_chunker.py
@@ -57,6 +57,104 @@ def test_parse_empty_file():
     asyncio.run(run())
 
 
+def test_invalid_utf8_is_replaced_without_modifying_source():
+    """Bad source bytes degrade the derived index but remain untouched on disk."""
+
+    async def run():
+        with tempfile.TemporaryDirectory() as tmp, temp_chdir(tmp):
+            source = b"# valid\ncontent before \xcd content after\n"
+            path = os.path.join(tmp, "invalid.md")
+            with open(path, "wb") as f:
+                f.write(source)
+
+            chunker = MarkdownFileChunker()
+            with patch.object(chunker.logger, "warning") as warning:
+                node, chunks = await chunker.chunk("invalid.md")
+
+            assert node.path == "invalid.md"
+            assert "content before \ufffd content after" in "\n".join(chunk.text for chunk in chunks)
+            with open(path, "rb") as f:
+                assert f.read() == source
+            warning.assert_called_once_with(
+                "Invalid utf-8 in invalid.md at byte 23 (bytes: cd); "
+                "indexed with replacement characters; source file unchanged",
+            )
+
+    asyncio.run(run())
+
+
+def test_invalid_utf8_strict_policy_still_raises():
+    """Strict mode remains available when callers require exact decoding."""
+
+    async def run():
+        with tempfile.TemporaryDirectory() as tmp, temp_chdir(tmp):
+            with open(os.path.join(tmp, "invalid.md"), "wb") as f:
+                f.write(b"valid\xcdinvalid")
+
+            chunker = MarkdownFileChunker(invalid_encoding_policy="strict")
+            try:
+                await chunker.chunk("invalid.md")
+            except UnicodeDecodeError as exc:
+                assert exc.start == 5
+            else:
+                raise AssertionError("strict policy must reject invalid UTF-8")
+
+    asyncio.run(run())
+
+
+def test_constructor_preserves_positional_arguments():
+    """The decoding policy must not shift the established positional parameters."""
+    chunker = MarkdownFileChunker("utf-8", 5000, False, 10, True, ["name"])
+
+    assert chunker.encoding == "utf-8"
+    assert chunker.chunk_byte_size == 5000
+    assert chunker.embed_toc is False
+    assert chunker.max_ast_sections == 10
+    assert chunker.include_frontmatter_in_metadata is True
+    assert chunker.include_frontmatter_keys_in_metadata == ["name"]
+
+
+def test_plain_text_fallback_normalizes_newlines():
+    """Markdown fallback chunks stay stable for equivalent platform newlines."""
+
+    async def run():
+        with tempfile.TemporaryDirectory() as tmp, temp_chdir(tmp):
+            path = os.path.join(tmp, "fallback.md")
+            with open(path, "wb") as f:
+                f.write(b"# One\r\nbody\r# Two\r\nbody\r\n")
+
+            chunker = MarkdownFileChunker(max_ast_sections=0)
+            _, original_chunks = await chunker.chunk("fallback.md")
+            with open(path, "wb") as f:
+                f.write(b"# One\nbody\n# Two\nbody\n")
+            _, normalized_chunks = await chunker.chunk("fallback.md")
+
+            assert [chunk.text for chunk in original_chunks] == [chunk.text for chunk in normalized_chunks]
+            assert [chunk.id for chunk in original_chunks] == [chunk.id for chunk in normalized_chunks]
+
+    asyncio.run(run())
+
+
+def test_invalid_ascii_is_replaced_for_markdown():
+    """Markdown byte accounting accepts the configured codec's replacement text."""
+
+    async def run():
+        with tempfile.TemporaryDirectory() as tmp, temp_chdir(tmp):
+            source = b"# valid\ncontent before \xff content after\n"
+            path = os.path.join(tmp, "invalid.md")
+            with open(path, "wb") as f:
+                f.write(source)
+
+            chunker = MarkdownFileChunker(encoding="ascii")
+            _, chunks = await chunker.chunk("invalid.md")
+
+            assert "content before ? content after" in "\n".join(chunk.text for chunk in chunks)
+            with open(path, "rb") as f:
+                assert f.read() == source
+
+    asyncio.run(run())
+
+
 def test_parse_frontmatter_only():
     """A file with only frontmatter (no body) → no chunks, no links."""