fix: use node factory for single-step workflow nodes

[hjlarry]

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Summary

fix #30858

Screenshots

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Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint and make type-check (backend) and cd web && npx lint-staged (frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @hjlarry, 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 resolves a critical issue causing a 500 error when attempting to execute a single code node within the workflow engine. The fix ensures that code nodes are instantiated with appropriate execution limits, preventing potential resource exhaustion or security vulnerabilities, and thereby enhancing the robustness and reliability of the workflow's code execution capabilities.

Highlights

• CodeNode Initialization Fix: Corrected the initialization of CodeNode instances in the single_step_run function to properly include CodeNodeLimits.
• CodeNodeLimits Configuration: Introduced CodeNodeLimits configuration, drawing values from dify_config, to ensure safe execution of code nodes by setting constraints on string length, number values, precision, and array lengths.
• New Unit Test: Added a new unit test (test_single_step_run_injects_code_limits) to validate that CodeNodeLimits are correctly passed to CodeNode during single-step workflow execution.

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[hjlarry]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors the single_step_run method in WorkflowEntry to use DifyNodeFactory for creating node instances. This is an excellent change that centralizes node creation logic and correctly handles the instantiation of nodes with specific dependency injection requirements, such as CodeNode. The previous direct instantiation was brittle and would fail for such nodes. A new unit test has been added to verify that CodeNode is correctly configured with its limits during a single-step run, confirming the fix. The changes are well-implemented, improve the code's robustness and maintainability, and I have no further suggestions.