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 acc545a8..4fddc632 100644
--- a/reme/components/file_chunker/default_file_chunker.py
+++ b/reme/components/file_chunker/default_file_chunker.py
@@ -22,9 +22,10 @@ class DefaultFileChunker(BaseFileChunker):
     def __init__(
         self,
         encoding: str = "utf-8",
-        invalid_encoding_policy: InvalidEncodingPolicy = "replace",
         chunk_byte_size: int = 10000,
         overlap_byte_size: int = 100,
+        *,
+        invalid_encoding_policy: InvalidEncodingPolicy = "replace",
         **kwargs,
     ):
         super().__init__(**kwargs)
@@ -57,7 +58,7 @@ class DefaultFileChunker(BaseFileChunker):
         async with aiofiles.open(file_path, "rb") as f:
             data = await f.read()
         try:
-            return data.decode(self.encoding)
+            text = data.decode(self.encoding)
         except UnicodeDecodeError as exc:
             if self.invalid_encoding_policy == "strict":
                 raise
@@ -66,7 +67,14 @@ class DefaultFileChunker(BaseFileChunker):
                 f"Invalid {self.encoding} in {file_path} at byte {exc.start} (bytes: {invalid_bytes}); "
                 "indexed with replacement characters; source file unchanged",
             )
-            return data.decode(self.encoding, errors="replace")
+            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)
diff --git a/reme/components/file_chunker/markdown_file_chunker.py b/reme/components/file_chunker/markdown_file_chunker.py
index a01e3e82..06a07793 100644
--- a/reme/components/file_chunker/markdown_file_chunker.py
+++ b/reme/components/file_chunker/markdown_file_chunker.py
@@ -103,12 +103,13 @@ class MarkdownFileChunker(DefaultFileChunker):
     def __init__(
         self,
         encoding: str = "utf-8",
-        invalid_encoding_policy: InvalidEncodingPolicy = "replace",
         chunk_byte_size: int = 10000,
         embed_toc: bool = True,
         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__(
diff --git a/tests/unit/test_default_file_chunker.py b/tests/unit/test_default_file_chunker.py
index d5bbdf23..aebd19ba 100644
--- a/tests/unit/test_default_file_chunker.py
+++ b/tests/unit/test_default_file_chunker.py
@@ -107,6 +107,59 @@ def test_invalid_encoding_policy_is_validated():
         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 54676607..fbeeffaf 100644
--- a/tests/unit/test_markdown_file_chunker.py
+++ b/tests/unit/test_markdown_file_chunker.py
@@ -102,6 +102,59 @@ def test_invalid_utf8_strict_policy_still_raises():
     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."""