fix: `SimpleTextSplitter` fallback 在文件解析链路中报错：缺少 `protect_urls`

[Lilili-04]

Pre-submission checklist | 提交前检查

• I have searched existing issues and this hasn't been mentioned before | 我已搜索现有问题，确认此问题尚未被提及
• I have read the project documentation and confirmed this issue doesn't already exist | 我已阅读项目文档并确认此问题尚未存在
• This issue is specific to MemOS and not a general software issue | 该问题是针对 MemOS 的，而不是一般软件问题

Bug Description | 问题描述

在处理会进入多模态文件解析链路的 /product/add 请求时，MemOS 可能在文本切分阶段出现如下错误：

[FileContentParser] Error splitting text: 'SimpleTextSplitter' object has no attribute 'protect_urls'

问题发生在 fallback 文本切分器路径中：当正常的 CharacterTextChunker / MarkdownChunker 初始化失败时，代码会退回使用 SimpleTextSplitter。但是 SimpleTextSplitter 内部调用了 self.protect_urls(text) 和 self.restore_urls(...)，而这两个方法实际定义在 BaseChunker 中，SimpleTextSplitter 既没有继承 BaseChunker，也没有自己实现这两个方法。

相关代码路径：

• src/memos/mem_reader/read_multi_modal/base.py
  • _split_text() 调用 get_text_splitter()，随后执行 splitter.chunk(text)。
• src/memos/mem_reader/read_multi_modal/utils.py
  • 如果 CharacterTextChunker / MarkdownChunker 初始化失败，get_text_splitter() 会返回 SimpleTextSplitter。
• src/memos/chunkers/simple_chunker.py
  • SimpleTextSplitter._simple_split_text() 调用了 self.protect_urls(text) 和 self.restore_urls(...)。
• src/memos/chunkers/base.py
  • protect_urls() 和 restore_urls() 定义在 BaseChunker 中。

因此，一旦 fallback 路径被真正触发，当前实现就会因为缺少方法而无法正常工作。

How to Reproduce | 如何重现

是在运行环境中让 langchain_text_splitters 不可用，或者让 CharacterTextChunker / MarkdownChunker 初始化失败，从而触发文件解析链路中的 SimpleTextSplitter fallback。

最小复现代码：

from memos.chunkers.simple_chunker import SimpleTextSplitter

splitter = SimpleTextSplitter(chunk_size=512, chunk_overlap=128)
splitter.chunk("This is a test document with a URL: https://example.com/path/to/resource")

期望结果：

文本可以被正常切分，并且 URL 不会被错误切断。

实际结果：

AttributeError: 'SimpleTextSplitter' object has no attribute 'protect_urls'

Environment | 环境信息

该问题是在 MemOS 从 ECS 迁移到 ACK 后观察到的。

• 部署目标：ACK
• API 路径：/product/add
• 解析链路：memos.mem_reader.read_multi_modal
• ACK 日志中观察到的出现次数：约 5,813 次
• 观察时间范围：2026-07-12 15:09:14 到 2026-07-14 15:14:50
• ECS 对比：ECS 日志中未观察到该错误

该错误分布在多个 ACK Pod IP 上，因此更像是镜像、依赖或运行时代码版本一致性问题，而不是单个请求或单台机器异常。

示例日志：

2026-07-14 14:06:27,820 | ... | path=/product/add | env=prod | user_type=normal | user_name=*** | memos.mem_reader.read_multi_modal.base - ERROR - base.py:275 - _split_text - [FileContentParser] Error splitting text: 'SimpleTextSplitter' object has no attribute 'protect_urls'

Additional Context | 其他信息

No response

Willingness to Implement | 实现意愿

• I'm willing to implement this myself | 我愿意自己解决
• I would like someone else to implement this | 我希望其他人来解决

[Memtensor-AI]

🤖 AutoDev has picked up this issue and started working on it.

Task ID: e062b03201f62d58
Working branch: bugfix/autodev-2115-20260716073650486
Target branch: latest dev* branch
Workflow: opsp (analysis → coding → testing → PR)

I will post the PR link here once done. If I need more information, I will ask in the comments.

[Memtensor-AI]

✅ AutoDev task e062b03201f62d58 completed.

Summary: Fixes issue #2115: SimpleTextSplitter fallback in the multi-modal file-parsing pipeline was raising AttributeError: 'SimpleTextSplitter' object has no attribute 'protect_urls'. Root cause: SimpleTextSplitter._simple_split_text() calls self.protect_urls / self.restore_urls, but those helpers live on BaseChunker and SimpleTextSplitter does not inherit from it. On ACK (where langchain_text_splitters is missing and the fallback is actually exercised) this produced ~5.8k noisy log rows and silently degraded chunking to a single-chunk pass-through.

The fix extracts protect_urls / restore_urls into a small URLProtectionMixin in src/memos/chunkers/base.py; BaseChunker now inherits it (behavioural no-op — same public API), and SimpleTextSplitter in src/memos/chunkers/simple_chunker.py also inherits it, so the two paths share one URL regex and one placeholder scheme. SimpleTextSplitter's constructor signature and chunk() -> list[str] return type are unchanged; no factory / config / OpenAPI changes are required.

Verification: 7 new regression tests in tests/chunkers/test_simple_chunker.py (short/long input with URL, empty / whitespace input, no-URL text, parametrised chunk sizes) — all 7 failed before the fix with the exact AttributeError, all 7 pass after. Broader pytest tests/chunkers/ tests/mem_reader/ → 63 pass; the 2 unrelated failures (test_doc_local_file, test_doc_mixed) fail identically on the pristine branch with the change stashed and are caused by the sandbox missing markitdown[all]. ruff check + ruff format --check are green on all 3 changed files.

Working branch pushed to origin; opsp task + verification report archived to memos-autodev-specs main. Ready for reviewer @WeiminLee.

Base branch: main
Branch: bugfix/autodev-2115-20260716073650486
Commit: 74d8598
PR: #2116
Assigned to: @NydiaChung
Reviewers: @WeiminLee