fix: #24292 HTTP Request Node Unable to Access File from Start Node When Using Remote URL in Workflow API Call

[dlmu-lq]

…hen Using Remote URL in Workflow API Call

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Summary

Fixes #24292

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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 dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[Copilot]

Pull Request Overview

This PR fixes an issue where the HTTP Request Node was unable to access files from the Start Node when using remote URLs in workflow API calls. The fix expands the file handling logic to properly process files that use remote URL transfer method.

• Adds proper handling for files with remote URL transfer method in HTTP request body initialization
• Imports the FileTransferMethod enum to support the new conditional logic

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