fix(channels): skip empty text blocks in DingTalk rich text parsing

[mvanhorn]

Summary

DingTalk richText messages can contain empty or whitespace-only text items. The current _parse_rich_content method creates TextContent(text="") blocks from these, which causes LLM API errors:

{"type":"error","error":{"type":"invalid_request_error","message":"messages: text content blocks must be non-empty"}}

The error persists because corrupted messages are stored in session history, requiring manual session file deletion to recover.

Changes

• dingtalk/handler.py: Strip text before appending and skip if empty, matching the guard pattern already used in the Feishu channel (as suggested in #1303 comment)
• base.py: Change the empty content_parts fallback from text="" to text=" " as a defensive measure against the same error class
• test_dingtalk_rich_text.py: Add regression tests verifying empty text items are filtered while valid text is preserved

Scope

This fix is intentionally scoped to the DingTalk handler and base fallback. The prior attempt (#1331) moved filtering into the shared build_agent_request_from_user_content, which was broader than needed. This PR keeps the change minimal and channel-specific.

Fixes #1303

This contribution was developed with AI assistance (Claude Code).

[gemini-code-assist]

Summary of Changes

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This pull request addresses an issue where DingTalk rich text messages containing empty or whitespace-only text items led to LLM API errors and corrupted session history. The changes prevent these invalid text blocks from being processed by stripping text content and skipping empty results in the DingTalk handler, and by providing a more robust fallback for empty content parts in the base channel utility. This ensures message integrity and prevents API failures.

Highlights

• DingTalk Rich Text Parsing Fix: Implemented a fix in the DingTalk channel handler to prevent empty or whitespace-only text blocks from being processed, resolving LLM API errors caused by invalid content.
• Defensive Fallback for Empty Content: Updated the base channel utility to use a single space as a fallback for empty text content, providing a more robust default and preventing similar API errors in other contexts.
• New Unit Tests: Added comprehensive unit tests specifically for DingTalk rich text parsing to ensure that empty and whitespace-only text items are correctly filtered out while valid text is preserved.

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Changelog

• src/copaw/app/channels/base.py
  • Changed the default TextContent for empty content_parts from an empty string to a single space to prevent LLM API errors.
• src/copaw/app/channels/dingtalk/handler.py
  • Modified the _parse_rich_content method to strip whitespace from text items and only append TextContent if the stripped text is not empty.
• tests/unit/channels/init.py
  • Added an empty init.py file to the tests/unit/channels directory.
• tests/unit/channels/test_dingtalk_rich_text.py
  • Added new test cases to verify that _parse_rich_content correctly skips empty and whitespace-only text items.
  • Included tests to confirm that valid text items are preserved and correctly stripped.

Activity

• This pull request was authored by mvanhorn.
• The changes were developed with AI assistance (Claude Code).
• This PR specifically fixes issue [Bug]: DingTalk Channel cannot handle rich text content #1303, which reported LLM API errors due to empty text blocks.
• The scope of this fix is intentionally minimal and channel-specific, contrasting with a broader prior attempt (fix(channels): filter empty text blocks from DingTalk rich text (#1303) #1331).

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[gemini-code-assist]

Code Review

This pull request effectively addresses a crash caused by empty text blocks from DingTalk rich text messages. The fix in dingtalk/handler.py to filter out empty or whitespace-only text items is correct and well-implemented. The addition of regression tests in test_dingtalk_rich_text.py ensures this issue won't reappear. The defensive change in base.py to use a single space as a fallback for empty content is a pragmatic solution that avoids API errors while integrating well with the existing debouncing logic. I have one minor suggestion for code simplification.

[xieyxclack]

Thank you for your contribution! Please remove the test files. And run pre-commit run --all-files to format the code

[github-actions]

Welcome to CoPaw! 🎉

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[mvanhorn]

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