fix(discord): split messages exceeding Discord's 2000 character limit

[Atletico1999]

Description

Discord's API rejects messages longer than 2000 characters. When CoPaw generates a long response (e.g. code blocks, detailed explanations), the send() call fails with 400 Bad Request, leaving the user with no reply.

This PR adds automatic message chunking to DiscordChannel:

• Adds _DISCORD_MAX_LEN class constant (2000 chars)
• Adds _chunk_text() static method that splits at newline boundaries to preserve markdown formatting.
• Fence-aware Chunking: Tracks the open/close state of markdown code fences ( ``` and ~~~) via _FENCE_RE. If a chunk splits in the middle of a code block, it automatically appends a closing fence to the current message and prepends an opening fence to the next message. This ensures code syntax highlighting is never broken across messages.
• Updated send() to iterate over chunks for both channel and DM targets.

Related Issue: N/A (discovered in production)

Security Considerations: None — only affects outbound message formatting.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• Refactoring

Component(s) Affected

• Core / Backend (app, agents, config, providers, utils, local_models)
• Console (frontend web UI)
• Channels (DingTalk, Feishu, QQ, Discord, iMessage, etc.)
• Skills
• CLI
• Documentation (website)
• Tests
• CI/CD
• Scripts / Deploy

Checklist

• I ran pre-commit run --all-files locally and it passes
• If pre-commit auto-fixed files, I committed those changes and reran checks
• I ran tests locally (pytest or as relevant) and they pass
• Documentation updated (if needed)
• Ready for review

Testing

1. Connect CoPaw to a Discord server
2. Ask the bot a question that generates a large code block > 2000 chars (e.g. "write a very long python backend script").
3. Before fix: Bot fails to reply (400 Bad Request on Discord API).
4. After fix: Bot replies with sequential messages. If the split happens inside a code block, both messages will render as properly formatted code blocks.

Additional Notes

• All other Discord features, including access control logic, meta passing, and media sending, remain entirely untouched and pure.
• The file was rewritten from a clean upstream base to guarantee LF endings and no UTF-16/BOM artifacts.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical issue where CoPaw's responses exceeding Discord's 2000-character limit would fail to send. By introducing automatic message chunking, the system can now reliably deliver long responses across multiple messages, ensuring users receive complete information. Additionally, the DiscordChannel class has been simplified by removing deprecated access control and media handling logic, making it more focused on core text communication.

Highlights

• Discord Message Chunking: Implemented automatic message splitting for Discord messages exceeding the 2000-character limit. Messages are now chunked at newline boundaries to preserve markdown formatting, with a hard-split fallback for single lines that are too long.
• Simplified DiscordChannel Initialization: Removed dm_policy, group_policy, allow_from, and deny_message parameters from the DiscordChannel constructor and related configuration methods, streamlining the channel's setup.
• Refactored Message Sending Logic: The send method in DiscordChannel was updated to incorporate the new message chunking logic. The _resolve_target, send_content_parts, and send_media methods were removed, indicating a consolidation or removal of media and complex content part handling within this class.

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Changelog

• src/copaw/app/channels/discord_/channel.py
  • Removed unused imports for tempfile, pathlib, urllib.parse, and OutgoingContentPart.
  • Removed dm_policy, group_policy, allow_from, and deny_message parameters from the __init__ method.
  • Removed is_group and _check_allowlist logic from the on_message handler.
  • Removed allow_from environment variable parsing and related parameters from the from_env method.
  • Removed dm_policy, group_policy, allow_from, and deny_message parameters from the from_config method.
  • Removed the _resolve_target method, consolidating its logic directly into the send method.
  • Added _DISCORD_MAX_LEN class constant to define Discord's message character limit.
  • Implemented the _chunk_text static method to split long messages into Discord-compliant chunks.
  • Refactored the send method to utilize the new _chunk_text method, iterating and sending multiple messages if necessary.
  • Removed the send_content_parts and send_media methods, simplifying the message sending interface.
  • Updated a comment in the _route_from_handle method for clarity.

Activity

• Atletico1999 created the pull request to fix Discord message length issues.
• The author has marked the pull request as ready for review.

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[gemini-code-assist]

Code Review

This pull request successfully adds message chunking to prevent errors with long messages on Discord. However, it also introduces two critical regressions by removing major features that don't seem related to the main goal of the PR.
Specifically:

1. Access Control Removed: The allowlist functionality (dm_policy, group_policy, etc.) has been completely removed, which could expose the bot to unintended users.
2. Media Sending Broken: The ability to send media files (images, videos, etc.) has been removed, as the send_media method implementation is gone.

These changes are not documented in the PR description and should be addressed.

Additionally, I've found an opportunity to simplify the new _chunk_text method by removing some unreachable code, which will improve its readability and maintainability.

[xieyxclack]

Please run pre-commit run --all-files to reformat the code

[Atletico1999]

Hi @xieyxclack , I have successfully re-applied the fixes as surgical patches on top of the latest upstream "channel.py" and formatted it. All upstream features (like access control and media sending) are strictly preserved now! Regarding the CI pre-commit failure in #1001, it seems to stem from a Windows CRLF vs LF issue on some unrelated website UI files. Could you please help review the functionality and approve the workflows? Thanks!

[xieyxclack]

@Atletico1999 Of course! Thank you very much for your contribution :)

[Leirunlin]

@Atletico1999 Hi, Thanks for the pr! I reviewed the code and found some tiny issues.

1. Duplicate BOM line (line 1-2)
   A UTF-8 BOM was prepended, creating a duplicate # -- coding: utf-8 -- line. Please remove it.

2. Corrupted comment (line 516)
   The Chinese character 或 in _route_from_handle was corrupted to 鎴? — likely a Windows encoding issue. Please fix or replace with English.

3. Suggestion: code fence awareness
   The current _chunk_text() splits at newline boundaries, which can break markdown code blocks across chunks.
   For example:

Chunk 1: "Here's the code:\n```python\ndef foo():\n    ..."

Chunk 2: "    return bar\n```"   ← missing opening fence, renders as plain text

This is a common long-message scenario (code explanations). Consider tracking fence state during chunking:

• Detect ```/~~~ open/close lines
• When flushing a chunk with an open fence, reserve space and append a closing fence
• Re-emit the opening fence at the start of the next chunk

This would keep code blocks properly formatted across split messages.

If you don't mind, I can help you fix the above issues and check it together. If you have any better suggestions, feel free to discuss.

[Atletico1999]

Hi @Leirunlin , thanks for the detailed review!

Regarding the three issues:

1. BOM / duplicate coding line — this was caused by my Windows dev environment (PowerShell UTF-16LE redirection). I've been fighting this across several pushes but the root cause is my local git encoding config. I'll set up core.autocrlf and .gitattributes properly and push a clean version.

2. Corrupted 或 → 鎴? — same encoding issue. Will fix in the next push.

3. Code fence awareness — good suggestion. Tracking ``` state during chunking to auto-close/re-open fences across chunks would definitely improve the output for code-heavy responses. Happy to add that.

I also noticed #1073 covers the same problem and brought up some good points (tests, lint). If it makes sense, I can incorporate those improvements (tests + the explicit DISCORD_SEND_CHUNK_SIZE constant) into this PR so everything is in one place, including the code fence handling you suggested. Or if you'd rather go with #1073 as the base, I'm fine with that too — the main thing is getting the fix landed.

Will push the encoding fixes shortly.

[Leirunlin]

Hi @Atletico1999, thanks again for the PR and for iterating so quickly.

We’d like to use your implementation as the base, so you can just keep updating this PR.

If either BOM / duplicate coding line or corruption is annoying to fix on your side, you can leave it to me.

Once 3) fence-aware chunking is added, I’m happy to take another review pass.

[Atletico1999]

Hi @Leirunlin , thanks for making this the base!

I just force-pushed a clean version that includes all three fixes:

1. BOM / duplicate coding line: Gone. I rewrote the file from a clean upstream base and fixed my local .gitattributes to ensure LF endings.
2. Corrupted comment: Fixed. The Chinese character was replaced with English or to avoid future Windows encoding issues entirely.
3. Fence-aware chunking: Implemented via regex (_FENCE_RE). It now tracks the open/close state of ``` and ~~~ fences, auto-closing them at the chunk boundary and re-opening them in the next chunk.

Sorry for the initial encoding mess 😅. It's fully clean and ready for your review whenever you get a chance!

[Leirunlin]

Great! I have tested the new commit locally and it looks good to me.

[github-actions]

Welcome to CoPaw! 🎉

Thank you @Atletico1999 for your first contribution! Your PR has been merged. 🚀

We'd love to give you a shout-out in our release notes! If you're comfortable sharing, please reply to this comment with your social media handles using the format below:

discord: your_discord_handle
x: your_x_handle
xiaohongshu: your_xiaohongshu_id

Note: Only share what you're comfortable with — all fields are optional.

Thanks again for helping make CoPaw better!