fix: interpolate {{ variables }} in Agentflow v2 nodes

[hztBUAA]

Summary

• {{ variable }} placeholders in Agentflow v2 nodes were not being interpolated with actual values
• Added content field to HumanInput node output (user feedback or action type) so {{ humanInputAgentflow_0 }} resolves correctly
• Improved fallback in resolveNodeReference: when a node is found but has no content or http.data, the entire output is stringified instead of returning the raw template string

Closes #5704

Test plan

• Create an agentflow: Start -> Human Input -> (Proceed) -> Direct Reply with {{ humanInputAgentflow_0 }}
• Verify the Direct Reply shows the user's feedback text (or "proceed"/"reject" when no feedback)
• Verify other node variable references (e.g., {{ llmAgentflow_0 }}) continue to work correctly

[gemini-code-assist]

Summary of Changes

Hello @hztBUAA, 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 bug in Agentflow v2 where variable placeholders were not being correctly interpolated, leading to unrendered dynamic content. The changes introduce a new content field for HumanInput node outputs and implement a more robust fallback mechanism for variable resolution, significantly improving the reliability and functionality of Agentflow workflows that rely on dynamic data.

Highlights

• Agentflow v2 Variable Interpolation Fix: Resolved an issue where {{ variable }} placeholders within Agentflow v2 nodes were not correctly interpolating with their actual values.
• HumanInput Node Output Enhancement: A content field was added to the HumanInput node's output, ensuring that {{ humanInputAgentflow_0 }} variables correctly resolve to user feedback or action types.
• Improved Variable Resolution Fallback: Enhanced the resolveNodeReference function to stringify the entire node output as a fallback when a node is found but lacks content or http.data, preventing raw template strings from being returned.

Changelog

• packages/components/nodes/agentflow/HumanInput/HumanInput.ts
  • Added a 'content' field to the output object of the HumanInput node, populating it with either user feedback or the action type.
• packages/server/src/utils/buildAgentflow.ts
  • Modified the 'resolveVariables' function to include a new conditional logic for 'formattedValue', introducing a fallback to stringify the entire 'nodeOutput' if 'actualValue' (content or http.data) is null or undefined.

Activity

• No human activity has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request fixes variable interpolation in Agentflow v2 nodes by ensuring the HumanInput node provides a content field and improving the fallback mechanism in resolveVariables. The logic now correctly handles cases where specific output fields are missing by stringifying the entire output object, which enhances the flexibility of template variables across different node types. A minor improvement to type safety for formattedValue has also been suggested.

[gemini-code-assist]

The variable formattedValue is always assigned a string value in all execution paths (via JSON.stringify, toString(), or the match string). Specifying the string type instead of any improves type safety and code clarity.

                let formattedValue: string

[hztBUAA]

Thanks for the review and feedback. I am following up on this PR now and will either push the requested changes or reply point-by-point shortly.

[hztBUAA]

Quick follow-up: I am reviewing the feedback and will update this PR shortly.

[HenryHengZJ]

Closing as #5818 with similar fix