feat: support passthrough propagation to plugins

[ywqwancbx]

Passthrough Propagation to Plugins

• Add top-level passthrough to InvokePluginRequest and Session, and include it in Session.Message() so it reaches the Python SDK as a first-class field (similar to conversation_id).
• Keep InvokeTool data payload strictly for business parameters; carry passthrough via session to avoid schema drift.
• Remove temporary debug logs and unused helpers; retain only necessary code for passthrough propagation.
• Backward compatible; existing tools continue to work without changes.
• Corresponding upstream changes in Dify main repo: feat: add passthrough parameter support for workflow tools.

[gemini-code-assist]

Summary of Changes

Hello @ywqwancbx, 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 introduces a flexible passthrough mechanism to enable the seamless propagation of additional, non-business-critical data to plugins. By integrating a dedicated passthrough field into core session and plugin invocation structures, it ensures that extra context can be carried through the system and made available to the Python SDK, all while preserving the integrity of existing InvokeTool schemas and maintaining full backward compatibility.

Highlights

• Passthrough Field Introduction: A new passthrough field has been added to InvokePluginRequest and Session structs to allow for the propagation of additional, arbitrary data to plugins.
• Python SDK Integration: The passthrough data is now included in the Session.Message() output, ensuring it reaches the Python SDK as a first-class field, similar to conversation_id.
• Schema Integrity: The InvokeTool data payload remains strictly for business parameters, preventing schema drift and maintaining a clean separation of concerns for passthrough data via the session.
• Backward Compatibility: The changes are fully backward compatible, meaning existing tools will continue to function without any modifications.

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[gemini-code-assist]

Code Review

This pull request introduces support for passthrough propagation to plugins by adding a passthrough field to InvokePluginRequest and Session structs. The changes are logical and correctly implemented to pass this new field through the system. My review found one minor formatting issue that should be addressed for code consistency.

[gemini-code-assist]

The indentation for the new Passthrough field is using spaces instead of a tab. Standard Go formatting, enforced by tools like gofmt, uses tabs for indentation. Please correct the indentation to maintain code style consistency.

Suggested change

	Passthrough *string `json:"passthrough"`
	Passthrough *string `json:"passthrough"`